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-rw-r--r--guix/records.scm32
1 files changed, 29 insertions, 3 deletions
diff --git a/guix/records.scm b/guix/records.scm
index 244b124098..99507dc384 100644
--- a/guix/records.scm
+++ b/guix/records.scm
@@ -118,6 +118,7 @@ of TYPE matches the expansion-time ABI."
((_ type name ctor (expected ...)
#:abi-cookie abi-cookie
#:thunked thunked
+ #:this-identifier this-identifier
#:delayed delayed
#:innate innate
#:defaults defaults)
@@ -162,7 +163,7 @@ of TYPE matches the expansion-time ABI."
(define (wrap-field-value f value)
(cond ((thunked-field? f)
#`(lambda (x)
- (syntax-parameterize ((this-record
+ (syntax-parameterize ((#,this-identifier
(lambda (s)
(syntax-case s ()
(id
@@ -254,6 +255,7 @@ may look like this:
(define-record-type* <thing> thing make-thing
thing?
+ this-thing
(name thing-name (default \"chbouib\"))
(port thing-port
(default (current-output-port)) (thunked))
@@ -273,7 +275,8 @@ default value specified in the 'define-record-type*' form is used:
The 'port' field is \"thunked\", meaning that calls like '(thing-port x)' will
actually compute the field's value in the current dynamic extent, which is
-useful when referring to fluids in a field's value.
+useful when referring to fluids in a field's value. Furthermore, that thunk
+can access the record it belongs to via the 'this-thing' identifier.
A field can also be marked as \"delayed\" instead of \"thunked\", in which
case its value is effectively wrapped in a (delay …) form.
@@ -352,7 +355,9 @@ inherited."
(syntax-case s ()
((_ type syntactic-ctor ctor pred
+ this-identifier
(field get properties ...) ...)
+ (identifier? #'this-identifier)
(let* ((field-spec #'((field get properties ...) ...))
(thunked (filter-map thunked-field? field-spec))
(delayed (filter-map delayed-field? field-spec))
@@ -381,15 +386,36 @@ inherited."
field-spec* ...)
(define #,(current-abi-identifier #'type)
#,cookie)
+
+ #,@(if (free-identifier=? #'this-identifier #'this-record)
+ #'()
+ #'((define-syntax-parameter this-identifier
+ (lambda (s)
+ "Return the record being defined. This macro may
+only be used in the context of the definition of a thunked field."
+ (syntax-case s ()
+ (id
+ (identifier? #'id)
+ (syntax-violation 'this-identifier
+ "cannot be used outside \
+of a record instantiation"
+ #'id)))))))
thunked-field-accessor ...
delayed-field-accessor ...
(make-syntactic-constructor type syntactic-ctor ctor
(field ...)
#:abi-cookie #,cookie
#:thunked #,thunked
+ #:this-identifier #'this-identifier
#:delayed #,delayed
#:innate #,innate
- #:defaults #,defaults))))))))
+ #:defaults #,defaults)))))
+ ((_ type syntactic-ctor ctor pred
+ (field get properties ...) ...)
+ ;; When no 'this' identifier was specified, use 'this-record'.
+ #'(define-record-type* type syntactic-ctor ctor pred
+ this-record
+ (field get properties ...) ...)))))
(define* (alist->record alist make keys
#:optional (multiple-value-keys '()))