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-rw-r--r--guix/records.scm87
1 files changed, 76 insertions, 11 deletions
diff --git a/guix/records.scm b/guix/records.scm
index ed94c83dac..13463647c8 100644
--- a/guix/records.scm
+++ b/guix/records.scm
@@ -1,5 +1,5 @@
;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012-2022 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2018 Mark H Weaver <mhw@netris.org>
;;;
;;; This file is part of GNU Guix.
@@ -104,6 +104,10 @@ error-reporting purposes."
(()
#t)))))))
+(define-syntax map-fields
+ (lambda (x)
+ (syntax-violation 'map-fields "bad use of syntactic keyword" x x)))
+
(define-syntax-parameter this-record
(lambda (s)
"Return the record being defined. This macro may only be used in the
@@ -325,6 +329,15 @@ This expression returns a new object equal to 'x' except for its 'name'
field and its 'loc' field---the latter is marked as \"innate\", so it is not
inherited."
+ (define (rtd-identifier type)
+ ;; Return an identifier derived from TYPE to name its record type
+ ;; descriptor (RTD).
+ (let ((type-name (syntax->datum type)))
+ (datum->syntax
+ type
+ (string->symbol
+ (string-append "% " (symbol->string type-name) " rtd")))))
+
(define (field-default-value s)
(syntax-case s (default)
((field (default val) _ ...)
@@ -428,10 +441,31 @@ inherited."
field)))
field-spec)))
#`(begin
- (define-record-type type
+ (define-record-type #,(rtd-identifier #'type)
(ctor field ...)
pred
field-spec* ...)
+
+ ;; Rectify the vtable type name...
+ (set-struct-vtable-name! #,(rtd-identifier #'type) 'type)
+ (cond-expand
+ (guile-3
+ ;; ... and the record type name.
+ (struct-set! #,(rtd-identifier #'type) vtable-offset-user
+ 'type))
+ (else #f))
+
+ (define-syntax type
+ (lambda (s)
+ "This macro lets us query record type info at
+macro-expansion time."
+ (syntax-case s (map-fields)
+ ((_ map-fields macro)
+ #'(macro (field ...)))
+ (id
+ (identifier? #'id)
+ #'#,(rtd-identifier #'type)))))
+
(define #,(current-abi-identifier #'type)
#,cookie)
@@ -535,19 +569,50 @@ pairs. Stop upon an empty line (after consuming it) or EOF."
(else
(error "unmatched line" line))))))))
+
+;;;
+;;; Pattern matching.
+;;;
+
+(define-syntax lookup-field
+ (lambda (s)
+ "Look up FIELD in the given list and return an expression that represents
+its offset in the record. Raise a syntax violation when the field is not
+found."
+ (syntax-case s ()
+ ((_ field offset ())
+ (syntax-violation 'lookup-field "unknown record type field"
+ s #'field))
+ ((_ field offset (head tail ...))
+ (free-identifier=? #'field #'head)
+ #'offset)
+ ((_ field offset (_ tail ...))
+ #'(lookup-field field (+ 1 offset) (tail ...))))))
+
+(define-syntax match-record-inner
+ (lambda (s)
+ (syntax-case s ()
+ ((_ record type (field rest ...) body ...)
+ #`(let-syntax ((field-offset (syntax-rules ()
+ ((_ f)
+ (lookup-field field 0 f)))))
+ (let* ((offset (type map-fields field-offset))
+ (field (struct-ref record offset)))
+ (match-record-inner record type (rest ...) body ...))))
+ ((_ record type () body ...)
+ #'(begin body ...)))))
+
(define-syntax match-record
(syntax-rules ()
"Bind each FIELD of a RECORD of the given TYPE to it's FIELD name.
+The order in which fields appear does not matter. A syntax error is raised if
+an unknown field is queried.
+
The current implementation does not support thunked and delayed fields."
- ((_ record type (field fields ...) body ...)
+ ;; TODO support thunked and delayed fields
+ ((_ record type (fields ...) body ...)
(if (eq? (struct-vtable record) type)
- ;; TODO compute indices and report wrong-field-name errors at
- ;; expansion time
- ;; TODO support thunked and delayed fields
- (let ((field ((record-accessor type 'field) record)))
- (match-record record type (fields ...) body ...))
- (throw 'wrong-type-arg record)))
- ((_ record type () body ...)
- (begin body ...))))
+ (match-record-inner record type (fields ...) body ...)
+ (throw 'wrong-type-arg record)))))
;;; records.scm ends here