diff options
Diffstat (limited to 'guix/records.scm')
| -rw-r--r-- | guix/records.scm | 87 |
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 |