Merge branch 'master' into core-updates

 Conflicts:
	gnu/local.mk
	gnu/packages/python-xyz.scm
	gnu/packages/xml.scm
	guix/gexp.scm
	po/guix/POTFILES.in

20 files changed, 739 insertions, 283 deletions

diff --git a/guix/channels.scm b/guix/channels.scm
index e7278c6060..e6bb9b891b 100644
--- a/guix/channels.scm
+++ b/guix/channels.scm
@@ -349,13 +349,15 @@ INSTANCES."
     (resolve-dependencies instances))
 
   (define (instance->derivation instance)
-    (mcached (if (eq? instance core-instance)
-                 (build-channel-instance instance)
-                 (mlet %store-monad ((core (instance->derivation core-instance))
-                                     (deps (mapm %store-monad instance->derivation
-                                                 (edges instance))))
-                   (build-channel-instance instance core deps)))
-             instance))
+    (mlet %store-monad ((system (current-system)))
+      (mcached (if (eq? instance core-instance)
+                   (build-channel-instance instance)
+                   (mlet %store-monad ((core (instance->derivation core-instance))
+                                       (deps (mapm %store-monad instance->derivation
+                                                   (edges instance))))
+                     (build-channel-instance instance core deps)))
+               instance
+               system)))
 
   (unless core-instance
     (let ((loc (and=> (any (compose channel-location channel-instance-channel)
@@ -429,32 +431,27 @@ derivation."
 (define (channel-instances->manifest instances)
   "Return a profile manifest with entries for all of INSTANCES, a list of
 channel instances."
-  (define instance->entry
-    (match-lambda
-      ((instance drv)
-       (let ((commit  (channel-instance-commit instance))
-             (channel (channel-instance-channel instance)))
-         (with-monad %store-monad
-           (return (manifest-entry
-                     (name (symbol->string (channel-name channel)))
-                     (version (string-take commit 7))
-                     (item (if (guix-channel? channel)
-                               (if (old-style-guix? drv)
-                                   (whole-package-for-legacy
-                                    (string-append name "-" version)
-                                    drv)
-                                   drv)
-                               drv))
-                     (properties
-                      `((source (repository
-                                 (version 0)
-                                 (url ,(channel-url channel))
-                                 (branch ,(channel-branch channel))
-                                 (commit ,commit))))))))))))
+  (define (instance->entry instance drv)
+    (let ((commit  (channel-instance-commit instance))
+          (channel (channel-instance-channel instance)))
+      (manifest-entry
+        (name (symbol->string (channel-name channel)))
+        (version (string-take commit 7))
+        (item (if (guix-channel? channel)
+                  (if (old-style-guix? drv)
+                      (whole-package-for-legacy (string-append name "-" version)
+                                                drv)
+                      drv)
+                  drv))
+        (properties
+         `((source (repository
+                    (version 0)
+                    (url ,(channel-url channel))
+                    (branch ,(channel-branch channel))
+                    (commit ,commit))))))))
 
   (mlet* %store-monad ((derivations (channel-instance-derivations instances))
-                       (entries     (mapm %store-monad instance->entry
-                                          (zip instances derivations))))
+                       (entries ->  (map instance->entry instances derivations)))
     (return (manifest entries))))
 
 (define (package-cache-file manifest)
diff --git a/guix/derivations.scm b/guix/derivations.scm
index 186d7a3f8f..731f1f698f 100644
--- a/guix/derivations.scm
+++ b/guix/derivations.scm
@@ -293,74 +293,78 @@ result is the set of prerequisites of DRV not already in valid."
             (derivation-output-path (assoc-ref outputs sub-drv)))
           sub-drvs))))
 
-(define* (substitution-oracle store drv
+(define* (substitution-oracle store inputs-or-drv
                               #:key (mode (build-mode normal)))
   "Return a one-argument procedure that, when passed a store file name,
 returns a 'substitutable?' if it's substitutable and #f otherwise.
-The returned procedure
-knows about all substitutes for all the derivations listed in DRV, *except*
-those that are already valid (that is, it won't bother checking whether an
-item is substitutable if it's already on disk); it also knows about their
-prerequisites, unless they are themselves substitutable.
+
+The returned procedure knows about all substitutes for all the derivation
+inputs or derivations listed in INPUTS-OR-DRV, *except* those that are already
+valid (that is, it won't bother checking whether an item is substitutable if
+it's already on disk); it also knows about their prerequisites, unless they
+are themselves substitutable.
 
 Creating a single oracle (thus making a single 'substitutable-path-info' call) and
 reusing it is much more efficient than calling 'has-substitutes?' or similar
 repeatedly, because it avoids the costs associated with launching the
 substituter many times."
-  (define valid?
-    (cut valid-path? store <>))
-
   (define valid-input?
     (cut valid-derivation-input? store <>))
 
-  (define (dependencies drv)
-    ;; Skip prerequisite sub-trees of DRV whose root is valid.  This allows us
-    ;; to ask the substituter for just as much as needed, instead of asking it
-    ;; for the whole world, which can be significantly faster when substitute
-    ;; info is not already in cache.
-    ;; Also, skip derivations marked as non-substitutable.
-    (append-map (lambda (input)
+  (define (closure inputs)
+    (let loop ((inputs inputs)
+               (closure '())
+               (visited (set)))
+      (match inputs
+        (()
+         (reverse closure))
+        ((input rest ...)
+         (let ((key (derivation-input-key input)))
+           (cond ((set-contains? visited key)
+                  (loop rest closure visited))
+                 ((valid-input? input)
+                  (loop rest closure (set-insert key visited)))
+                 (else
                   (let ((drv (derivation-input-derivation input)))
-                    (if (substitutable-derivation? drv)
-                        (derivation-input-output-paths input)
-                        '())))
-                (derivation-prerequisites drv valid-input?)))
-
-  (let* ((paths (delete-duplicates
-                 (concatenate
-                  (fold (lambda (drv result)
-                          (let ((self (match (derivation->output-paths drv)
-                                        (((names . paths) ...)
-                                         paths))))
-                            (cond ((eqv? mode (build-mode check))
-                                   (cons (dependencies drv) result))
-                                  ((not (substitutable-derivation? drv))
-                                   (cons (dependencies drv) result))
-                                  ((every valid? self)
-                                   result)
-                                  (else
-                                   (cons* self (dependencies drv) result)))))
-                        '()
-                        drv))))
-         (subst (fold (lambda (subst vhash)
-                        (vhash-cons (substitutable-path subst) subst
-                                    vhash))
-                      vlist-null
-                      (substitutable-path-info store paths))))
+                    (loop (append (derivation-inputs drv) rest)
+                          (if (substitutable-derivation? drv)
+                              (cons input closure)
+                              closure)
+                          (set-insert key visited))))))))))
+
+  (let* ((inputs (closure (map (match-lambda
+                                 ((? derivation-input? input)
+                                  input)
+                                 ((? derivation? drv)
+                                  (derivation-input drv)))
+                               inputs-or-drv)))
+         (items  (append-map derivation-input-output-paths inputs))
+         (subst  (fold (lambda (subst vhash)
+                         (vhash-cons (substitutable-path subst) subst
+                                     vhash))
+                       vlist-null
+                       (substitutable-path-info store items))))
     (lambda (item)
       (match (vhash-assoc item subst)
         (#f #f)
         ((key . value) value)))))
 
+(define (dependencies-of-substitutables substitutables inputs)
+  "Return the subset of INPUTS whose output file names is among the references
+of SUBSTITUTABLES."
+  (let ((items (fold set-insert (set)
+                     (append-map substitutable-references substitutables))))
+    (filter (lambda (input)
+              (any (cut set-contains? items <>)
+                   (derivation-input-output-paths input)))
+            inputs)))
+
 (define* (derivation-build-plan store inputs
                                 #:key
                                 (mode (build-mode normal))
                                 (substitutable-info
                                  (substitution-oracle
-                                  store
-                                  (map derivation-input-derivation
-                                       inputs)
-                                  #:mode mode)))
+                                  store inputs #:mode mode)))
   "Given INPUTS, a list of derivation-inputs, return two values: the list of
 derivation to build, and the list of substitutable items that, together,
 allows INPUTS to be realized.
@@ -391,7 +395,9 @@ by 'substitution-oracle'."
       (()
        (values build substitute))
       ((input rest ...)
-       (let ((key (derivation-input-key input)))
+       (let ((key  (derivation-input-key input))
+             (deps (derivation-inputs
+                    (derivation-input-derivation input))))
          (cond ((set-contains? visited key)
                 (loop rest build substitute visited))
                ((input-built? input)
@@ -400,16 +406,17 @@ by 'substitution-oracle'."
                ((input-substitutable-info input)
                 =>
                 (lambda (substitutables)
-                  (loop rest build
+                  (loop (append (dependencies-of-substitutables substitutables
+                                                                deps)
+                                rest)
+                        build
                         (append substitutables substitute)
                         (set-insert key visited))))
                (else
-                (let ((deps (derivation-inputs
-                             (derivation-input-derivation input))))
-                  (loop (append deps rest)
-                        (cons (derivation-input-derivation input) build)
-                        substitute
-                        (set-insert key visited))))))))))
+                (loop (append deps rest)
+                      (cons (derivation-input-derivation input) build)
+                      substitute
+                      (set-insert key visited)))))))))
 
 (define-deprecated (derivation-prerequisites-to-build store drv #:rest rest)
   derivation-build-plan
diff --git a/guix/discovery.scm b/guix/discovery.scm
index 5bb494941b..86f20ec344 100644
--- a/guix/discovery.scm
+++ b/guix/discovery.scm
@@ -78,7 +78,9 @@ DIRECTORY is not accessible."
                                  ((= stat:type 'directory)
                                   (append (scheme-files absolute)
                                           result))
-                                 (_ result)))))
+                                 (_ result)))
+                              (else
+                               result)))
                        (else
                         result))))))
               '()
diff --git a/guix/docker.scm b/guix/docker.scm
index 7fe83d9797..b1bd226fa1 100644
--- a/guix/docker.scm
+++ b/guix/docker.scm
@@ -73,7 +73,7 @@
   `((,(generate-tag path) . ((latest . ,id)))))
 
 ;; See https://github.com/opencontainers/image-spec/blob/master/config.md
-(define* (config layer time arch #:key entry-point)
+(define* (config layer time arch #:key entry-point (environment '()))
   "Generate a minimal image configuration for the given LAYER file."
   ;; "architecture" must be values matching "platform.arch" in the
   ;; runtime-spec at
@@ -81,9 +81,13 @@
   `((architecture . ,arch)
     (comment . "Generated by GNU Guix")
     (created . ,time)
-    (config . ,(if entry-point
-                   `((entrypoint . ,entry-point))
-                   #nil))
+    (config . ,`((env . ,(map (match-lambda
+                                ((name . value)
+                                 (string-append name "=" value)))
+                              environment))
+                 ,@(if entry-point
+                       `((entrypoint . ,entry-point))
+                       '())))
     (container_config . #nil)
     (os . "linux")
     (rootfs . ((type . "layers")
@@ -113,6 +117,7 @@ return \"a\"."
                              (system (utsname:machine (uname)))
                              database
                              entry-point
+                             (environment '())
                              compressor
                              (creation-time (current-time time-utc)))
   "Write to IMAGE a Docker image archive containing the given PATHS.  PREFIX
@@ -124,6 +129,9 @@ When DATABASE is true, copy it to /var/guix/db in the image and create
 When ENTRY-POINT is true, it must be a list of strings; it is stored as the
 entry point in the Docker image JSON structure.
 
+ENVIRONMENT must be a list of name/value pairs.  It specifies the environment
+variables that must be defined in the resulting image.
+
 SYMLINKS must be a list of (SOURCE -> TARGET) tuples describing symlinks to be
 created in the image, where each TARGET is relative to PREFIX.
 TRANSFORMATIONS must be a list of (OLD -> NEW) tuples describing how to
@@ -234,6 +242,7 @@ SRFI-19 time-utc object, as the creation time in metadata."
         (lambda ()
           (scm->json (config (string-append id "/layer.tar")
                              time arch
+                             #:environment environment
                              #:entry-point entry-point))))
       (with-output-to-file "manifest.json"
         (lambda ()
diff --git a/guix/gexp.scm b/guix/gexp.scm
index 9bf68a91f4..186bce19a8 100644
--- a/guix/gexp.scm
+++ b/guix/gexp.scm
@@ -39,6 +39,9 @@
 
             gexp-input
             gexp-input?
+            gexp-input-thing
+            gexp-input-output
+            gexp-input-native?
 
             local-file
             local-file?
@@ -78,6 +81,14 @@
             load-path-expression
             gexp-modules
 
+            lower-gexp
+            lowered-gexp?
+            lowered-gexp-sexp
+            lowered-gexp-inputs
+            lowered-gexp-guile
+            lowered-gexp-load-path
+            lowered-gexp-load-compiled-path
+
             gexp->derivation
             gexp->file
             gexp->script
@@ -566,15 +577,20 @@ list."
   "Turn any package from INPUTS into a derivation for SYSTEM; return the
 corresponding input list as a monadic value.  When TARGET is true, use it as
 the cross-compilation target triplet."
+  (define (store-item? obj)
+    (and (string? obj) (store-path? obj)))
+
   (with-monad %store-monad
     (mapm %store-monad
           (match-lambda
             (((? struct? thing) sub-drv ...)
              (mlet %store-monad ((drv (lower-object
                                        thing system #:target target)))
-               (return `(,drv ,@sub-drv))))
+               (return (apply gexp-input drv sub-drv))))
+            (((? store-item? item))
+             (return (gexp-input item)))
             (input
-             (return input)))
+             (return (gexp-input input))))
           inputs)))
 
 (define* (lower-reference-graphs graphs #:key system target)
@@ -586,7 +602,9 @@ corresponding derivation."
      (mlet %store-monad ((inputs (lower-inputs inputs
                                                #:system system
                                                #:target target)))
-       (return (map cons file-names inputs))))))
+       (return (map (lambda (file input)
+                      (cons file (gexp-input->tuple input)))
+                    file-names inputs))))))
 
 (define* (lower-references lst #:key system target)
   "Based on LST, a list of output names and packages, return a list of output
@@ -618,6 +636,127 @@ names and file names suitable for the #:allowed-references argument to
     (lambda (system)
       ((force proc) system))))
 
+;; Representation of a gexp instantiated for a given target and system.
+(define-record-type <lowered-gexp>
+  (lowered-gexp sexp inputs guile load-path load-compiled-path)
+  lowered-gexp?
+  (sexp                lowered-gexp-sexp)         ;sexp
+  (inputs              lowered-gexp-inputs)       ;list of <gexp-input>
+  (guile               lowered-gexp-guile)        ;<derivation> | #f
+  (load-path           lowered-gexp-load-path)    ;list of store items
+  (load-compiled-path  lowered-gexp-load-compiled-path)) ;list of store items
+
+(define* (lower-gexp exp
+                     #:key
+                     (module-path %load-path)
+                     (system (%current-system))
+                     (target 'current)
+                     (graft? (%graft?))
+                     (guile-for-build (%guile-for-build))
+                     (effective-version "2.2")
+
+                     deprecation-warnings)
+  "*Note: This API is subject to change; use at your own risk!*
+
+Lower EXP, a gexp, instantiating it for SYSTEM and TARGET.  Return a
+<lowered-gexp> ready to be used.
+
+Lowered gexps are an intermediate representation that's useful for
+applications that deal with gexps outside in a way that is disconnected from
+derivations--e.g., code evaluated for its side effects."
+  (define %modules
+    (delete-duplicates (gexp-modules exp)))
+
+  (define (search-path modules extensions suffix)
+    (append (match modules
+              ((? derivation? drv)
+               (list (derivation->output-path drv)))
+              (#f
+               '())
+              ((? store-path? item)
+               (list item)))
+            (map (lambda (extension)
+                   (string-append (match extension
+                                    ((? derivation? drv)
+                                     (derivation->output-path drv))
+                                    ((? store-path? item)
+                                     item))
+                                  suffix))
+                 extensions)))
+
+  (mlet* %store-monad ( ;; The following binding forces '%current-system' and
+                       ;; '%current-target-system' to be looked up at >>=
+                       ;; time.
+                       (graft?    (set-grafting graft?))
+
+                       (system -> (or system (%current-system)))
+                       (target -> (if (eq? target 'current)
+                                      (%current-target-system)
+                                      target))
+                       (guile     (if guile-for-build
+                                      (return guile-for-build)
+                                      (default-guile-derivation system)))
+                       (normals  (lower-inputs (gexp-inputs exp)
+                                               #:system system
+                                               #:target target))
+                       (natives  (lower-inputs (gexp-native-inputs exp)
+                                               #:system system
+                                               #:target #f))
+                       (inputs -> (append normals natives))
+                       (sexp     (gexp->sexp exp
+                                             #:system system
+                                             #:target target))
+                       (extensions -> (gexp-extensions exp))
+                       (exts     (mapm %store-monad
+                                       (lambda (obj)
+                                         (lower-object obj system))
+                                       extensions))
+                       (modules  (if (pair? %modules)
+                                     (imported-modules %modules
+                                                       #:system system
+                                                       #:module-path module-path)
+                                     (return #f)))
+                       (compiled (if (pair? %modules)
+                                     (compiled-modules %modules
+                                                       #:system system
+                                                       #:module-path module-path
+                                                       #:extensions extensions
+                                                       #:guile guile
+                                                       #:deprecation-warnings
+                                                       deprecation-warnings)
+                                     (return #f))))
+    (define load-path
+      (search-path modules exts
+                   (string-append "/share/guile/site/" effective-version)))
+
+    (define load-compiled-path
+      (search-path compiled exts
+                   (string-append "/lib/guile/" effective-version
+                                  "/site-ccache")))
+
+    (mbegin %store-monad
+      (set-grafting graft?)                       ;restore the initial setting
+      (return (lowered-gexp sexp
+                            `(,@(if modules
+                                    (list (gexp-input modules))
+                                    '())
+                              ,@(if compiled
+                                    (list (gexp-input compiled))
+                                    '())
+                              ,@(map gexp-input exts)
+                              ,@inputs)
+                            guile
+                            load-path
+                            load-compiled-path)))))
+
+(define (gexp-input->tuple input)
+  "Given INPUT, a <gexp-input> record, return the corresponding input tuple
+suitable for the 'derivation' procedure."
+  (match (gexp-input-output input)
+    ("out"  `(,(gexp-input-thing input)))
+    (output `(,(gexp-input-thing input)
+              ,(gexp-input-output input)))))
+
 (define* (gexp->derivation name exp
                            #:key
                            system (target 'current)
@@ -676,10 +815,8 @@ DEPRECATION-WARNINGS determines whether to show deprecation warnings while
 compiling modules.  It can be #f, #t, or 'detailed.
 
 The other arguments are as for 'derivation'."
-  (define %modules
-    (delete-duplicates
-     (append modules (gexp-modules exp))))
   (define outputs (gexp-outputs exp))
+  (define requested-graft? graft?)
 
   (define (graphs-file-names graphs)
     ;; Return a list of (FILE-NAME . STORE-PATH) pairs made from GRAPHS.
@@ -693,11 +830,13 @@ The other arguments are as for 'derivation'."
             (cons file-name thing)))
          graphs))
 
-  (define (extension-flags extension)
-    `("-L" ,(string-append (derivation->output-path extension)
-                           "/share/guile/site/" effective-version)
-      "-C" ,(string-append (derivation->output-path extension)
-                           "/lib/guile/" effective-version "/site-ccache")))
+  (define (add-modules exp modules)
+    (if (null? modules)
+        exp
+        (make-gexp (gexp-references exp)
+                   (append modules (gexp-self-modules exp))
+                   (gexp-self-extensions exp)
+                   (gexp-proc exp))))
 
   (mlet* %store-monad ( ;; The following binding forces '%current-system' and
                        ;; '%current-target-system' to be looked up at >>=
@@ -708,38 +847,19 @@ The other arguments are as for 'derivation'."
                        (target -> (if (eq? target 'current)
                                       (%current-target-system)
                                       target))
-                       (normals  (lower-inputs (gexp-inputs exp)
-                                               #:system system
-                                               #:target target))
-                       (natives  (lower-inputs (gexp-native-inputs exp)
-                                               #:system system
-                                               #:target #f))
-                       (inputs -> (append normals natives))
-                       (sexp     (gexp->sexp exp
-                                             #:system system
-                                             #:target target))
-                       (builder  (text-file script-name
-                                            (object->string sexp)))
-                       (extensions -> (gexp-extensions exp))
-                       (exts     (mapm %store-monad
-                                       (lambda (obj)
-                                         (lower-object obj system))
-                                       extensions))
-                       (modules  (if (pair? %modules)
-                                     (imported-modules %modules
-                                                       #:system system
-                                                       #:module-path module-path
-                                                       #:guile guile-for-build)
-                                     (return #f)))
-                       (compiled (if (pair? %modules)
-                                     (compiled-modules %modules
-                                                       #:system system
-                                                       #:module-path module-path
-                                                       #:extensions extensions
-                                                       #:guile guile-for-build
-                                                       #:deprecation-warnings
-                                                       deprecation-warnings)
-                                     (return #f)))
+                       (exp ->    (add-modules exp modules))
+                       (lowered   (lower-gexp exp
+                                              #:module-path module-path
+                                              #:system system
+                                              #:target target
+                                              #:graft? requested-graft?
+                                              #:guile-for-build
+                                              guile-for-build
+                                              #:effective-version
+                                              effective-version
+                                              #:deprecation-warnings
+                                              deprecation-warnings))
+
                        (graphs   (if references-graphs
                                      (lower-reference-graphs references-graphs
                                                              #:system system
@@ -755,32 +875,30 @@ The other arguments are as for 'derivation'."
                                                          #:system system
                                                          #:target target)
                                        (return #f)))
-                       (guile    (if guile-for-build
-                                     (return guile-for-build)
-                                     (default-guile-derivation system))))
+                       (guile -> (lowered-gexp-guile lowered))
+                       (builder  (text-file script-name
+                                            (object->string
+                                             (lowered-gexp-sexp lowered)))))
     (mbegin %store-monad
       (set-grafting graft?)                       ;restore the initial setting
       (raw-derivation name
                       (string-append (derivation->output-path guile)
                                      "/bin/guile")
                       `("--no-auto-compile"
-                        ,@(if (pair? %modules)
-                              `("-L" ,(if (derivation? modules)
-                                          (derivation->output-path modules)
-                                          modules)
-                                "-C" ,(derivation->output-path compiled))
-                              '())
-                        ,@(append-map extension-flags exts)
+                        ,@(append-map (lambda (directory)
+                                        `("-L" ,directory))
+                                      (lowered-gexp-load-path lowered))
+                        ,@(append-map (lambda (directory)
+                                        `("-C" ,directory))
+                                      (lowered-gexp-load-compiled-path lowered))
                         ,builder)
                       #:outputs outputs
                       #:env-vars env-vars
                       #:system system
                       #:inputs `((,guile)
                                  (,builder)
-                                 ,@(if modules
-                                       `((,modules) (,compiled) ,@inputs)
-                                       inputs)
-                                 ,@(map list exts)
+                                 ,@(map gexp-input->tuple
+                                        (lowered-gexp-inputs lowered))
                                  ,@(match graphs
                                      (((_ . inputs) ...) inputs)
                                      (_ '())))
@@ -796,6 +914,7 @@ The other arguments are as for 'derivation'."
 (define* (gexp-inputs exp #:key native?)
   "Return the input list for EXP.  When NATIVE? is true, return only native
 references; otherwise, return only non-native references."
+  ;; TODO: Return <gexp-input> records instead of tuples.
   (define (add-reference-inputs ref result)
     (match ref
       (($ <gexp-input> (? gexp? exp) _ #t)
diff --git a/guix/inferior.scm b/guix/inferior.scm
index 63c95141d7..fee97750b6 100644
--- a/guix/inferior.scm
+++ b/guix/inferior.scm
@@ -59,6 +59,7 @@
             inferior-eval
             inferior-eval-with-store
             inferior-object?
+            read-repl-response
 
             inferior-packages
             inferior-available-packages
@@ -183,7 +184,8 @@ equivalent.  Return #f if the inferior could not be launched."
 
 (set-record-type-printer! <inferior-object> write-inferior-object)
 
-(define (read-inferior-response inferior)
+(define (read-repl-response port)
+  "Read a (guix repl) response from PORT and return it as a Scheme object."
   (define sexp->object
     (match-lambda
       (('value value)
@@ -191,12 +193,15 @@ equivalent.  Return #f if the inferior could not be launched."
       (('non-self-quoting address string)
        (inferior-object address string))))
 
-  (match (read (inferior-socket inferior))
+  (match (read port)
     (('values objects ...)
      (apply values (map sexp->object objects)))
     (('exception key objects ...)
      (apply throw key (map sexp->object objects)))))
 
+(define (read-inferior-response inferior)
+  (read-repl-response (inferior-socket inferior)))
+
 (define (send-inferior-request exp inferior)
   (write exp (inferior-socket inferior))
   (newline (inferior-socket inferior)))
diff --git a/guix/remote.scm b/guix/remote.scm
new file mode 100644
index 0000000000..e503c76167
--- /dev/null
+++ b/guix/remote.scm
@@ -0,0 +1,134 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix remote)
+  #:use-module (guix ssh)
+  #:use-module (guix gexp)
+  #:use-module (guix inferior)
+  #:use-module (guix store)
+  #:use-module (guix monads)
+  #:use-module (guix modules)
+  #:use-module (guix derivations)
+  #:use-module (ssh popen)
+  #:use-module (srfi srfi-1)
+  #:use-module (ice-9 match)
+  #:export (remote-eval))
+
+;;; Commentary:
+;;;
+;;; Note: This API is experimental and subject to change!
+;;;
+;;; Evaluate a gexp on a remote machine, over SSH, ensuring that all the
+;;; elements the gexp refers to are deployed beforehand.  This is useful for
+;;; expressions that have side effects; for pure expressions, you would rather
+;;; build a derivation remotely or offload it.
+;;;
+;;; Code:
+
+(define (remote-pipe-for-gexp lowered session)
+  "Return a remote pipe for the given SESSION to evaluate LOWERED."
+  (define shell-quote
+    (compose object->string object->string))
+
+  (apply open-remote-pipe* session OPEN_READ
+         (string-append (derivation->output-path
+                         (lowered-gexp-guile lowered))
+                        "/bin/guile")
+         "--no-auto-compile"
+         (append (append-map (lambda (directory)
+                               `("-L" ,directory))
+                             (lowered-gexp-load-path lowered))
+                 (append-map (lambda (directory)
+                               `("-C" ,directory))
+                             (lowered-gexp-load-path lowered))
+                 `("-c"
+                   ,(shell-quote (lowered-gexp-sexp lowered))))))
+
+(define (%remote-eval lowered session)
+  "Evaluate LOWERED, a lowered gexp, in SESSION.  This assumes that all the
+prerequisites of EXP are already available on the host at SESSION."
+  (let* ((pipe   (remote-pipe-for-gexp lowered session))
+         (result (read-repl-response pipe)))
+    (close-port pipe)
+    result))
+
+(define (trampoline exp)
+  "Return a \"trampoline\" gexp that evaluates EXP and writes the evaluation
+result to the current output port using the (guix repl) protocol."
+  (define program
+    (scheme-file "remote-exp.scm" exp))
+
+  (with-imported-modules (source-module-closure '((guix repl)))
+    #~(begin
+        (use-modules (guix repl))
+        (send-repl-response '(primitive-load #$program)
+                            (current-output-port))
+        (force-output))))
+
+(define* (remote-eval exp session
+                      #:key
+                      (build-locally? #t)
+                      (module-path %load-path)
+                      (socket-name "/var/guix/daemon-socket/socket"))
+  "Evaluate EXP, a gexp, on the host at SESSION, an SSH session.  Ensure that
+all the elements EXP refers to are built and deployed to SESSION beforehand.
+When BUILD-LOCALLY? is true, said dependencies are built locally and sent to
+the remote store afterwards; otherwise, dependencies are built directly on the
+remote store."
+  (mlet %store-monad ((lowered (lower-gexp (trampoline exp)
+                                           #:module-path %load-path))
+                      (remote -> (connect-to-remote-daemon session
+                                                           socket-name)))
+    (define inputs
+      (cons (gexp-input (lowered-gexp-guile lowered))
+            (lowered-gexp-inputs lowered)))
+
+    (define to-build
+      (map (lambda (input)
+             (if (derivation? (gexp-input-thing input))
+                 (cons (gexp-input-thing input)
+                       (gexp-input-output input))
+                 (gexp-input-thing input)))
+           inputs))
+
+    (if build-locally?
+        (let ((to-send (map (lambda (input)
+                              (match (gexp-input-thing input)
+                                ((? derivation? drv)
+                                 (derivation->output-path
+                                  drv (gexp-input-output input)))
+                                ((? store-path? item)
+                                 item)))
+                            inputs)))
+          (mbegin %store-monad
+            (built-derivations to-build)
+            ((store-lift send-files) to-send remote #:recursive? #t)
+            (return (close-connection remote))
+            (return (%remote-eval lowered session))))
+        (let ((to-send (map (lambda (input)
+                              (match (gexp-input-thing input)
+                                ((? derivation? drv)
+                                 (derivation-file-name drv))
+                                ((? store-path? item)
+                                 item)))
+                            inputs)))
+          (mbegin %store-monad
+            ((store-lift send-files) to-send remote #:recursive? #t)
+            (return (build-derivations remote to-build))
+            (return (close-connection remote))
+            (return (%remote-eval lowered session)))))))
diff --git a/guix/repl.scm b/guix/repl.scm
new file mode 100644
index 0000000000..5cff5c71e9
--- /dev/null
+++ b/guix/repl.scm
@@ -0,0 +1,86 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2018, 2019 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix repl)
+  #:use-module (rnrs bytevectors)
+  #:use-module (ice-9 match)
+  #:export (send-repl-response
+            machine-repl))
+
+;;; Commentary:
+;;;
+;;; This module implements the "machine-readable" REPL provided by
+;;; 'guix repl -t machine'.  It's a lightweight module meant to be
+;;; embedded in any Guile process providing REPL functionality.
+;;;
+;;; Code:
+
+(define (self-quoting? x)
+  "Return #t if X is self-quoting."
+  (letrec-syntax ((one-of (syntax-rules ()
+                            ((_) #f)
+                            ((_ pred rest ...)
+                             (or (pred x)
+                                 (one-of rest ...))))))
+    (one-of symbol? string? pair? null? vector?
+            bytevector? number? boolean?)))
+
+
+(define (send-repl-response exp output)
+  "Write the response corresponding to the evaluation of EXP to PORT, an
+output port."
+  (define (value->sexp value)
+    (if (self-quoting? value)
+        `(value ,value)
+        `(non-self-quoting ,(object-address value)
+                           ,(object->string value))))
+
+  (catch #t
+    (lambda ()
+      (let ((results (call-with-values
+                         (lambda ()
+                           (primitive-eval exp))
+                       list)))
+        (write `(values ,@(map value->sexp results))
+               output)
+        (newline output)
+        (force-output output)))
+    (lambda (key . args)
+      (write `(exception ,key ,@(map value->sexp args)))
+      (newline output)
+      (force-output output))))
+
+(define* (machine-repl #:optional
+                       (input (current-input-port))
+                       (output (current-output-port)))
+  "Run a machine-usable REPL over ports INPUT and OUTPUT.
+
+The protocol of this REPL is meant to be machine-readable and provides proper
+support to represent multiple-value returns, exceptions, objects that lack a
+read syntax, and so on.  As such it is more convenient and robust than parsing
+Guile's REPL prompt."
+  (write `(repl-version 0 0) output)
+  (newline output)
+  (force-output output)
+
+  (let loop ()
+    (match (read input)
+      ((? eof-object?) #t)
+      (exp
+       (send-repl-response exp output)
+       (loop)))))
diff --git a/guix/scripts/deploy.scm b/guix/scripts/deploy.scm
new file mode 100644
index 0000000000..978cfb2a81
--- /dev/null
+++ b/guix/scripts/deploy.scm
@@ -0,0 +1,84 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 David Thompson <davet@gnu.org>
+;;; Copyright © 2019 Jakob L. Kreuze <zerodaysfordays@sdf.lonestar.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix scripts deploy)
+  #:use-module (gnu machine)
+  #:use-module (guix scripts)
+  #:use-module (guix scripts build)
+  #:use-module (guix store)
+  #:use-module (guix ui)
+  #:use-module (ice-9 format)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-37)
+  #:export (guix-deploy))
+
+;;; Commentary:
+;;;
+;;; This program provides a command-line interface to (gnu machine), allowing
+;;; users to perform remote deployments through specification files.
+;;;
+;;; Code:
+
+
+
+(define (show-help)
+  (display (G_ "Usage: guix deploy [OPTION] FILE...
+Perform the deployment specified by FILE.\n"))
+  (show-build-options-help)
+  (newline)
+  (display (G_ "
+  -h, --help             display this help and exit"))
+  (display (G_ "
+  -V, --version          display version information and exit"))
+  (newline)
+  (show-bug-report-information))
+
+(define %options
+  (cons* (option '(#\h "help") #f #f
+                 (lambda args
+                   (show-help)
+                   (exit 0)))
+         %standard-build-options))
+
+(define %default-options
+  '((system . ,(%current-system))
+    (substitutes? . #t)
+    (build-hook? . #t)
+    (graft? . #t)
+    (debug . 0)
+    (verbosity . 1)))
+
+(define (load-source-file file)
+  "Load FILE as a user module."
+  (let ((module (make-user-module '((gnu) (gnu machine) (gnu machine ssh)))))
+    (load* file module)))
+
+(define (guix-deploy . args)
+  (define (handle-argument arg result)
+    (alist-cons 'file arg result))
+  (let* ((opts (parse-command-line args %options (list %default-options)
+                                   #:argument-handler handle-argument))
+         (file (assq-ref opts 'file))
+         (machines (or (and file (load-source-file file)) '())))
+    (with-store store
+      (set-build-options-from-command-line store opts)
+      (for-each (lambda (machine)
+                  (info (G_ "deploying to ~a...") (machine-display-name machine))
+                  (run-with-store store (deploy-machine machine)))
+                machines))))
diff --git a/guix/scripts/environment.scm b/guix/scripts/environment.scm
index ac269083c8..f7f7edda48 100644
--- a/guix/scripts/environment.scm
+++ b/guix/scripts/environment.scm
@@ -163,6 +163,10 @@ COMMAND or an interactive shell in that environment.\n"))
                          user into an isolated container, use the name USER
                          with home directory /home/USER"))
   (display (G_ "
+      --no-cwd           do not share current working directory with an
+                         isolated container"))
+
+  (display (G_ "
       --share=SPEC       for containers, share writable host file system
                          according to SPEC"))
   (display (G_ "
@@ -270,6 +274,9 @@ use '--preserve' instead~%"))
                  (lambda (opt name arg result)
                    (alist-cons 'user arg
                                (alist-delete 'user result eq?))))
+         (option '("no-cwd") #f #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'no-cwd? #t result)))
          (option '("share") #t #f
                  (lambda (opt name arg result)
                    (alist-cons 'file-system-mapping
@@ -445,7 +452,8 @@ regexps in WHITE-LIST."
            ((_ . status) status)))))
 
 (define* (launch-environment/container #:key command bash user user-mappings
-                                       profile manifest link-profile? network?)
+                                       profile manifest link-profile? network?
+                                       map-cwd?)
   "Run COMMAND within a container that features the software in PROFILE.
 Environment variables are set according to the search paths of MANIFEST.
 The global shell is BASH, a file name for a GNU Bash binary in the
@@ -480,26 +488,29 @@ will be used for the passwd entry.  LINK-PROFILE? creates a symbolic link from
             ;; /bin/sh, the current working directory, and possibly networking
             ;; configuration files within the container.
             (mappings
-             (override-user-mappings
-              user home
-              (append user-mappings
-                      ;; Current working directory.
-                      (list (file-system-mapping
-                             (source cwd)
-                             (target cwd)
-                             (writable? #t)))
-                      ;; When in Rome, do as Nix build.cc does: Automagically
-                      ;; map common network configuration files.
-                      (if network?
-                          %network-file-mappings
-                          '())
-                      ;; Mappings for the union closure of all inputs.
-                      (map (lambda (dir)
-                             (file-system-mapping
-                              (source dir)
-                              (target dir)
-                              (writable? #f)))
-                           reqs))))
+             (append
+              (override-user-mappings
+               user home
+               (append user-mappings
+                       ;; Share current working directory, unless asked not to.
+                       (if map-cwd?
+                           (list (file-system-mapping
+                                  (source cwd)
+                                  (target cwd)
+                                  (writable? #t)))
+                           '())))
+              ;; When in Rome, do as Nix build.cc does: Automagically
+              ;; map common network configuration files.
+              (if network?
+                  %network-file-mappings
+                  '())
+              ;; Mappings for the union closure of all inputs.
+              (map (lambda (dir)
+                     (file-system-mapping
+                      (source dir)
+                      (target dir)
+                      (writable? #f)))
+                   reqs)))
             (file-systems (append %container-file-systems
                                   (map file-system-mapping->bind-mount
                                        mappings))))
@@ -537,8 +548,10 @@ will be used for the passwd entry.  LINK-PROFILE? creates a symbolic link from
             (write-group groups)
 
             ;; For convenience, start in the user's current working
-            ;; directory rather than the root directory.
-            (chdir (override-user-dir user home cwd))
+            ;; directory or, if unmapped, the home directory.
+            (chdir (if map-cwd?
+                       (override-user-dir user home cwd)
+                       home-dir))
 
             (primitive-exit/status
              ;; A container's environment is already purified, so no need to
@@ -664,6 +677,7 @@ message if any test fails."
            (container? (assoc-ref opts 'container?))
            (link-prof? (assoc-ref opts 'link-profile?))
            (network?   (assoc-ref opts 'network?))
+           (no-cwd?    (assoc-ref opts 'no-cwd?))
            (user       (assoc-ref opts 'user))
            (bootstrap? (assoc-ref opts 'bootstrap?))
            (system     (assoc-ref opts 'system))
@@ -684,6 +698,9 @@ message if any test fails."
         (leave (G_ "'--link-profile' cannot be used without '--container'~%")))
       (when (and (not container?) user)
         (leave (G_ "'--user' cannot be used without '--container'~%")))
+      (when (and (not container?) no-cwd?)
+        (leave (G_ "--no-cwd cannot be used without --container~%")))
+
 
       (with-store store
         (with-status-verbosity (assoc-ref opts 'verbosity)
@@ -740,7 +757,9 @@ message if any test fails."
                                                     #:profile profile
                                                     #:manifest manifest
                                                     #:link-profile? link-prof?
-                                                    #:network? network?)))
+                                                    #:network? network?
+                                                    #:map-cwd? (not no-cwd?))))
+
                    (else
                     (return
                      (exit/status
diff --git a/guix/scripts/gc.scm b/guix/scripts/gc.scm
index 9a57e5fd1e..31657326b6 100644
--- a/guix/scripts/gc.scm
+++ b/guix/scripts/gc.scm
@@ -104,11 +104,14 @@ Invoke the garbage collector.\n"))
           '()))))
 
 (define (delete-old-generations store profile pattern)
-  "Remove the generations of PROFILE that match PATTERN, a duration pattern.
-Do nothing if none matches."
+  "Remove the generations of PROFILE that match PATTERN, a duration pattern;
+do nothing if none matches.  If PATTERN is #f, delete all generations but the
+current one."
   (let* ((current (generation-number profile))
-         (numbers (matching-generations pattern profile
-                                        #:duration-relation >)))
+         (numbers (if (not pattern)
+                      (profile-generations profile)
+                      (matching-generations pattern profile
+                                            #:duration-relation >))))
 
     ;; Make sure we don't inadvertently remove the current generation.
     (delete-generations store profile (delv current numbers))))
@@ -155,8 +158,7 @@ is deprecated; use '-D'~%"))
                         (when (and arg (not (string->duration arg)))
                           (leave (G_ "~s does not denote a duration~%")
                                  arg))
-                        (alist-cons 'delete-generations (or arg "")
-                                    result)))))
+                        (alist-cons 'delete-generations arg result)))))
         (option '("optimize") #f #f
                 (lambda (opt name arg result)
                   (alist-cons 'action 'optimize
@@ -287,9 +289,9 @@ is deprecated; use '-D'~%"))
          (assert-no-extra-arguments)
          (let ((min-freed  (assoc-ref opts 'min-freed))
                (free-space (assoc-ref opts 'free-space)))
-           (match (assoc-ref opts 'delete-generations)
+           (match (assq 'delete-generations opts)
              (#f #t)
-             ((? string? pattern)
+             ((_ . pattern)
               (delete-generations store pattern)))
            (cond
             (free-space
diff --git a/guix/scripts/pack.scm b/guix/scripts/pack.scm
index c8cb7b959d..1524607623 100644
--- a/guix/scripts/pack.scm
+++ b/guix/scripts/pack.scm
@@ -27,6 +27,7 @@
   #:use-module (guix utils)
   #:use-module (guix store)
   #:use-module ((guix status) #:select (with-status-verbosity))
+  #:use-module ((guix self) #:select (make-config.scm))
   #:use-module (guix grafts)
   #:autoload   (guix inferior) (inferior-package?)
   #:use-module (guix monads)
@@ -285,6 +286,32 @@ added to the pack."
                     build
                     #:references-graphs `(("profile" ,profile))))
 
+(define (singularity-environment-file profile)
+  "Return a shell script that defines the environment variables corresponding
+to the search paths of PROFILE."
+  (define build
+    (with-extensions (list guile-gcrypt)
+      (with-imported-modules `(((guix config) => ,(make-config.scm))
+                               ,@(source-module-closure
+                                  `((guix profiles)
+                                    (guix search-paths))
+                                  #:select? not-config?))
+        #~(begin
+            (use-modules (guix profiles) (guix search-paths)
+                         (ice-9 match))
+
+            (call-with-output-file #$output
+              (lambda (port)
+                (for-each (match-lambda
+                            ((spec . value)
+                             (format port "~a=~a~%export ~a~%"
+                                     (search-path-specification-variable spec)
+                                     value
+                                     (search-path-specification-variable spec))))
+                          (profile-search-paths #$profile))))))))
+
+  (computed-file "singularity-environment.sh" build))
+
 (define* (squashfs-image name profile
                          #:key target
                          (profile-name "guix-profile")
@@ -304,6 +331,9 @@ added to the pack."
          (file-append (store-database (list profile))
                       "/db/db.sqlite")))
 
+  (define environment
+    (singularity-environment-file profile))
+
   (define build
     (with-imported-modules (source-module-closure
                             '((guix build utils)
@@ -338,6 +368,7 @@ added to the pack."
                  `(,@(map store-info-item
                           (call-with-input-file "profile"
                             read-reference-graph))
+                   #$environment
                    ,#$output
 
                    ;; Do not perform duplicate checking because we
@@ -378,10 +409,19 @@ added to the pack."
                                                             target)))))))
                       '#$symlinks)
 
+                   "-p" "/.singularity.d d 555 0 0"
+
+                   ;; Create the environment file.
+                   "-p" "/.singularity.d/env d 555 0 0"
+                   "-p" ,(string-append
+                          "/.singularity.d/env/90-environment.sh s 777 0 0 "
+                          (relative-file-name "/.singularity.d/env"
+                                              #$environment))
+
                    ;; Create /.singularity.d/actions, and optionally the 'run'
                    ;; script, used by 'singularity run'.
-                   "-p" "/.singularity.d d 555 0 0"
                    "-p" "/.singularity.d/actions d 555 0 0"
+
                    ,@(if entry-point
                          `(;; This one if for Singularity 2.x.
                            "-p"
@@ -440,11 +480,24 @@ the image."
   (define build
     ;; Guile-JSON and Guile-Gcrypt are required by (guix docker).
     (with-extensions (list guile-json guile-gcrypt)
-      (with-imported-modules (source-module-closure '((guix docker)
-                                                      (guix build store-copy))
-                                                    #:select? not-config?)
+      (with-imported-modules `(((guix config) => ,(make-config.scm))
+                               ,@(source-module-closure
+                                  `((guix docker)
+                                    (guix build store-copy)
+                                    (guix profiles)
+                                    (guix search-paths))
+                                  #:select? not-config?))
         #~(begin
-            (use-modules (guix docker) (srfi srfi-19) (guix build store-copy))
+            (use-modules (guix docker) (guix build store-copy)
+                         (guix profiles) (guix search-paths)
+                         (srfi srfi-19) (ice-9 match))
+
+            (define environment
+              (map (match-lambda
+                     ((spec . value)
+                      (cons (search-path-specification-variable spec)
+                            value)))
+                   (profile-search-paths #$profile)))
 
             (setenv "PATH" (string-append #$archiver "/bin"))
 
@@ -455,6 +508,7 @@ the image."
                                 #$profile
                                 #:database #+database
                                 #:system (or #$target (utsname:machine (uname)))
+                                #:environment environment
                                 #:entry-point #$(and entry-point
                                                      #~(string-append #$profile "/"
                                                                       #$entry-point))
diff --git a/guix/scripts/package.scm b/guix/scripts/package.scm
index 7b277b63f1..a43c96516f 100644
--- a/guix/scripts/package.scm
+++ b/guix/scripts/package.scm
@@ -98,7 +98,7 @@ denote ranges as interpreted by 'matching-generations'."
     (cond ((not (file-exists? profile))            ; XXX: race condition
            (raise (condition (&profile-not-found-error
                               (profile profile)))))
-          ((string-null? pattern)
+          ((not pattern)
            (delete-generations store profile
                                (delv current (profile-generations profile))))
           ;; Do not delete the zeroth generation.
@@ -120,9 +120,7 @@ denote ranges as interpreted by 'matching-generations'."
              (let ((numbers (delv current numbers)))
                (when (null-list? numbers)
                  (leave (G_ "no matching generation~%")))
-               (delete-generations store profile numbers))))
-          (else
-           (leave (G_ "invalid syntax: ~a~%") pattern)))))
+               (delete-generations store profile numbers)))))))
 
 (define* (build-and-use-profile store profile manifest
                                 #:key
@@ -457,12 +455,12 @@ command-line option~%")
                            arg-handler)))
          (option '(#\l "list-generations") #f #t
                  (lambda (opt name arg result arg-handler)
-                   (values (cons `(query list-generations ,(or arg ""))
+                   (values (cons `(query list-generations ,arg)
                                  result)
                            #f)))
          (option '(#\d "delete-generations") #f #t
                  (lambda (opt name arg result arg-handler)
-                   (values (alist-cons 'delete-generations (or arg "")
+                   (values (alist-cons 'delete-generations arg
                                        result)
                            #f)))
          (option '(#\S "switch-generation") #t #f
@@ -683,7 +681,7 @@ processed, #f otherwise."
         (cond ((not (file-exists? profile))       ; XXX: race condition
                (raise (condition (&profile-not-found-error
                                   (profile profile)))))
-              ((string-null? pattern)
+              ((not pattern)
                (match (profile-generations profile)
                  (()
                   #t)
@@ -697,10 +695,7 @@ processed, #f otherwise."
                      (exit 1)
                      (begin
                        (list-generation display-profile-content (car numbers))
-                       (diff-profiles profile numbers)))))
-              (else
-               (leave (G_ "invalid syntax: ~a~%")
-                      pattern))))
+                       (diff-profiles profile numbers)))))))
        #t)
 
       (('list-installed regexp)
diff --git a/guix/scripts/pull.scm b/guix/scripts/pull.scm
index 2d428546c9..7895c19914 100644
--- a/guix/scripts/pull.scm
+++ b/guix/scripts/pull.scm
@@ -117,7 +117,7 @@ Download and deploy the latest version of Guix.\n"))
                    (alist-cons 'channel-file arg result)))
          (option '(#\l "list-generations") #f #t
                  (lambda (opt name arg result)
-                   (cons `(query list-generations ,(or arg ""))
+                   (cons `(query list-generations ,arg)
                          result)))
          (option '(#\N "news") #f #f
                  (lambda (opt name arg result)
@@ -486,7 +486,7 @@ list of package changes.")))))
       (cond ((not (file-exists? profile))         ; XXX: race condition
              (raise (condition (&profile-not-found-error
                                 (profile profile)))))
-            ((string-null? pattern)
+            ((not pattern)
              (list-generations profile (profile-generations profile)))
             ((matching-generations pattern profile)
              =>
diff --git a/guix/scripts/repl.scm b/guix/scripts/repl.scm
index 02169e8004..e1cc759fc8 100644
--- a/guix/scripts/repl.scm
+++ b/guix/scripts/repl.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2018 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2018, 2019 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -19,6 +19,7 @@
 (define-module (guix scripts repl)
   #:use-module (guix ui)
   #:use-module (guix scripts)
+  #:use-module (guix repl)
   #:use-module (guix utils)
   #:use-module (guix packages)
   #:use-module (gnu packages)
@@ -29,8 +30,7 @@
   #:autoload   (system repl repl) (start-repl)
   #:autoload   (system repl server)
                   (make-tcp-server-socket make-unix-domain-server-socket)
-  #:export (machine-repl
-            guix-repl))
+  #:export (guix-repl))
 
 ;;; Commentary:
 ;;;
@@ -68,62 +68,12 @@ Start a Guile REPL in the Guix execution environment.\n"))
   (newline)
   (show-bug-report-information))
 
-(define (self-quoting? x)
-  "Return #t if X is self-quoting."
-  (letrec-syntax ((one-of (syntax-rules ()
-                            ((_) #f)
-                            ((_ pred rest ...)
-                             (or (pred x)
-                                 (one-of rest ...))))))
-    (one-of symbol? string? pair? null? vector?
-            bytevector? number? boolean?)))
-
 (define user-module
   ;; Module where we execute user code.
   (let ((module (resolve-module '(guix-user) #f #f #:ensure #t)))
     (beautify-user-module! module)
     module))
 
-(define* (machine-repl #:optional
-                       (input (current-input-port))
-                       (output (current-output-port)))
-  "Run a machine-usable REPL over ports INPUT and OUTPUT.
-
-The protocol of this REPL is meant to be machine-readable and provides proper
-support to represent multiple-value returns, exceptions, objects that lack a
-read syntax, and so on.  As such it is more convenient and robust than parsing
-Guile's REPL prompt."
-  (define (value->sexp value)
-    (if (self-quoting? value)
-        `(value ,value)
-        `(non-self-quoting ,(object-address value)
-                           ,(object->string value))))
-
-  (write `(repl-version 0 0) output)
-  (newline output)
-  (force-output output)
-
-  (let loop ()
-    (match (read input)
-      ((? eof-object?) #t)
-      (exp
-       (catch #t
-         (lambda ()
-           (let ((results (call-with-values
-                              (lambda ()
-
-                                (primitive-eval exp))
-                            list)))
-             (write `(values ,@(map value->sexp results))
-                    output)
-             (newline output)
-             (force-output output)))
-         (lambda (key . args)
-           (write `(exception ,key ,@(map value->sexp args)))
-           (newline output)
-           (force-output output)))
-       (loop)))))
-
 (define (call-with-connection spec thunk)
   "Dynamically-bind the current input and output ports according to SPEC and
 call THUNK."
diff --git a/guix/scripts/system.scm b/guix/scripts/system.scm
index 60c1ca5c9a..67a4071684 100644
--- a/guix/scripts/system.scm
+++ b/guix/scripts/system.scm
@@ -614,7 +614,7 @@ PATTERN, a string.  When PATTERN is #f, display all the system generations."
   (cond ((not (file-exists? profile))             ; XXX: race condition
          (raise (condition (&profile-not-found-error
                             (profile profile)))))
-        ((string-null? pattern)
+        ((not pattern)
          (for-each display-system-generation (profile-generations profile)))
         ((matching-generations pattern profile)
          =>
@@ -622,9 +622,7 @@ PATTERN, a string.  When PATTERN is #f, display all the system generations."
            (if (null-list? numbers)
                (exit 1)
                (leave-on-EPIPE
-                (for-each display-system-generation numbers)))))
-        (else
-         (leave (G_ "invalid syntax: ~a~%") pattern))))
+                (for-each display-system-generation numbers)))))))
 
 
 ;;;
@@ -1232,7 +1230,7 @@ argument list and OPTS is the option alist."
     ;; an operating system configuration file.
     ((list-generations)
      (let ((pattern (match args
-                      (() "")
+                      (() #f)
                       ((pattern) pattern)
                       (x (leave (G_ "wrong number of arguments~%"))))))
        (list-generations pattern)))
@@ -1242,7 +1240,7 @@ argument list and OPTS is the option alist."
     ;; operating system configuration file.
     ((delete-generations)
      (let ((pattern (match args
-                      (() "")
+                      (() #f)
                       ((pattern) pattern)
                       (x (leave (G_ "wrong number of arguments~%"))))))
        (with-store store
diff --git a/guix/self.scm b/guix/self.scm
index 6a876bd822..249705fcee 100644
--- a/guix/self.scm
+++ b/guix/self.scm
@@ -770,7 +770,8 @@ Info manual."
                    (gnu services)
                    ,@(scheme-modules* source "gnu/bootloader")
                    ,@(scheme-modules* source "gnu/system")
-                   ,@(scheme-modules* source "gnu/services"))
+                   ,@(scheme-modules* source "gnu/services")
+                   ,@(scheme-modules* source "gnu/machine"))
                  (list *core-package-modules* *package-modules*
                        *extra-modules* *core-modules*)
                  #:extensions dependencies
diff --git a/guix/ssh.scm b/guix/ssh.scm
index 9b9baf54ea..ede00133c8 100644
--- a/guix/ssh.scm
+++ b/guix/ssh.scm
@@ -57,12 +57,14 @@
 (define %compression
   "zlib@openssh.com,zlib")
 
-(define* (open-ssh-session host #:key user port
+(define* (open-ssh-session host #:key user port identity
                            (compression %compression))
-  "Open an SSH session for HOST and return it.  When USER and PORT are #f, use
-default values or whatever '~/.ssh/config' specifies; otherwise use them.
-Throw an error on failure."
+  "Open an SSH session for HOST and return it.  IDENTITY specifies the file
+name of a private key to use for authenticating with the host.  When USER,
+PORT, or IDENTITY are #f, use default values or whatever '~/.ssh/config'
+specifies; otherwise use them.  Throw an error on failure."
   (let ((session (make-session #:user user
+                               #:identity identity
                                #:host host
                                #:port port
                                #:timeout 10       ;seconds
diff --git a/guix/store.scm b/guix/store.scm
index 52940ff751..d7c603898c 100644
--- a/guix/store.scm
+++ b/guix/store.scm
@@ -1802,11 +1802,12 @@ connection, and return the result."
     (call-with-values (lambda ()
                         (run-with-state mval store))
       (lambda (result new-store)
-        ;; Copy the object cache from NEW-STORE so we don't fully discard the
-        ;; state.
-        (let ((cache (store-connection-object-cache new-store)))
-          (set-store-connection-object-cache! store cache)
-          result)))))
+        (when (and store new-store)
+          ;; Copy the object cache from NEW-STORE so we don't fully discard
+          ;; the state.
+          (let ((cache (store-connection-object-cache new-store)))
+            (set-store-connection-object-cache! store cache)))
+        result))))
 
 
 ;;;
diff --git a/guix/ui.scm b/guix/ui.scm
index 6d243ef041..76f6fc8eed 100644
--- a/guix/ui.scm
+++ b/guix/ui.scm
@@ -835,8 +835,7 @@ check and report what is prerequisites are available for download."
     ;; substituter many times.  This makes a big difference, especially when
     ;; DRV is a long list as is the case with 'guix environment'.
     (if use-substitutes?
-        (substitution-oracle store (map derivation-input-derivation inputs)
-                             #:mode mode)
+        (substitution-oracle store inputs #:mode mode)
         (const #f)))
 
   (let*-values (((build download)
@@ -844,18 +843,6 @@ check and report what is prerequisites are available for download."
                                         #:mode mode
                                         #:substitutable-info
                                         substitutable-info))
-                ((download)                   ; add the references of DOWNLOAD
-                 (if use-substitutes?
-                     (delete-duplicates
-                      (append download
-                              (filter-map (lambda (item)
-                                            (if (valid-path? store item)
-                                                #f
-                                                (substitutable-info item)))
-                                          (append-map
-                                           substitutable-references
-                                           download))))
-                     download))
                 ((graft hook build)
                  (match (fold (lambda (drv acc)
                                 (let ((file (derivation-file-name drv)))
@@ -1497,7 +1484,11 @@ DURATION-RELATION with the current time."
         ((string->duration str)
          =>
          filter-by-duration)
-        (else #f)))
+        (else
+         (raise
+          (condition (&message
+                      (message (format #f (G_ "invalid syntax: ~a~%")
+                                       str))))))))
 
 (define (display-generation profile number)
   "Display a one-line summary of generation NUMBER of PROFILE."