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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2012, 2013, 2014, 2015 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 records)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-9)
#:use-module (srfi srfi-26)
#:use-module (ice-9 match)
#:use-module (ice-9 regex)
#:use-module (ice-9 rdelim)
#:export (define-record-type*
alist->record
object->fields
recutils->alist))
;;; Commentary:
;;;
;;; Utilities for dealing with Scheme records.
;;;
;;; Code:
(define-syntax record-error
(syntax-rules ()
"Report a syntactic error in use of CONSTRUCTOR."
((_ constructor form fmt args ...)
(syntax-violation constructor
(format #f fmt args ...)
form))))
(define-syntax define-record-type*
(lambda (s)
"Define the given record type such that an additional \"syntactic
constructor\" is defined, which allows instances to be constructed with named
field initializers, à la SRFI-35, as well as default values. An example use
may look like this:
(define-record-type* <thing> thing make-thing
thing?
(name thing-name (default \"chbouib\"))
(port thing-port
(default (current-output-port)) (thunked)))
This example defines a macro 'thing' that can be used to instantiate records
of this type:
(thing
(name \"foo\")
(port (current-error-port)))
The value of 'name' or 'port' could as well be omitted, in which case the
default value specified in the 'define-record-type*' form is used:
(thing)
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.
It is possible to copy an object 'x' created with 'thing' like this:
(thing (inherit x) (name \"bar\"))
This expression returns a new object equal to 'x' except for its 'name'
field."
(define* (make-syntactic-constructor type name ctor fields
#:key thunked defaults)
"Make the syntactic constructor NAME for TYPE, that calls CTOR, and
expects all of FIELDS to be initialized. DEFAULTS is the list of
FIELD/DEFAULT-VALUE tuples, and THUNKED is the list of identifiers of
thunked fields."
(with-syntax ((type type)
(name name)
(ctor ctor)
(expected fields)
(defaults defaults))
#`(define-syntax name
(lambda (s)
(define (record-inheritance orig-record field+value)
;; Produce code that returns a record identical to
;; ORIG-RECORD, except that values for the FIELD+VALUE alist
;; prevail.
(define (field-inherited-value f)
(and=> (find (lambda (x)
(eq? f (car (syntax->datum x))))
field+value)
car))
;; Make sure there are no unknown field names.
(let* ((fields (map (compose car syntax->datum)
field+value))
(unexpected (lset-difference eq? fields 'expected)))
(when (pair? unexpected)
(record-error 'name s "extraneous field initializers ~a"
unexpected)))
#`(make-struct type 0
#,@(map (lambda (field index)
(or (field-inherited-value field)
#`(struct-ref #,orig-record
#,index)))
'expected
(iota (length 'expected)))))
(define (thunked-field? f)
(memq (syntax->datum f) '#,thunked))
(define (field-bindings field+value)
;; Return field to value bindings, for use in 'let*' below.
(map (lambda (field+value)
(syntax-case field+value ()
((field value)
#`(field
#,(if (thunked-field? #'field)
#'(lambda () value)
#'value)))))
field+value))
(syntax-case s (inherit #,@fields)
((_ (inherit orig-record) (field value) (... ...))
#`(let* #,(field-bindings #'((field value) (... ...)))
#,(record-inheritance #'orig-record
#'((field value) (... ...)))))
((_ (field value) (... ...))
(let ((fields (map syntax->datum #'(field (... ...))))
(dflt (map (match-lambda
((f v)
(list (syntax->datum f) v)))
#'defaults)))
(define (field-value f)
(or (and=> (find (lambda (x)
(eq? f (car (syntax->datum x))))
#'((field value) (... ...)))
car)
(let ((value
(car (assoc-ref dflt
(syntax->datum f)))))
(if (thunked-field? f)
#`(lambda () #,value)
value))))
(let ((fields (append fields (map car dflt))))
(cond ((lset= eq? fields 'expected)
#`(let* #,(field-bindings
#'((field value) (... ...)))
(ctor #,@(map field-value 'expected))))
((pair? (lset-difference eq? fields 'expected))
(record-error 'name s
"extraneous field initializers ~a"
(lset-difference eq? fields
'expected)))
(else
(record-error 'name s
"missing field initializers ~a"
(lset-difference eq? 'expected
fields))))))))))))
(define (field-default-value s)
(syntax-case s (default)
((field (default val) _ ...)
(list #'field #'val))
((field _ options ...)
(field-default-value #'(field options ...)))
(_ #f)))
(define (thunked-field? s)
;; Return the field name if the field defined by S is thunked.
(syntax-case s (thunked)
((field (thunked) _ ...)
#'field)
((field _ options ...)
(thunked-field? #'(field options ...)))
(_ #f)))
(define (thunked-field-accessor-name field)
;; Return the name (an unhygienic syntax object) of the "real"
;; getter for field, which is assumed to be a thunked field.
(syntax-case field ()
((field get options ...)
(let* ((getter (syntax->datum #'get))
(real-getter (symbol-append '% getter '-real)))
(datum->syntax #'get real-getter)))))
(define (field-spec->srfi-9 field)
;; Convert a field spec of our style to a SRFI-9 field spec of the
;; form (field get).
(syntax-case field ()
((name get options ...)
#`(name
#,(if (thunked-field? field)
(thunked-field-accessor-name field)
#'get)))))
(define (thunked-field-accessor-definition field)
;; Return the real accessor for FIELD, which is assumed to be a
;; thunked field.
(syntax-case field ()
((name get _ ...)
(with-syntax ((real-get (thunked-field-accessor-name field)))
#'(define-inlinable (get x)
;; The real value of that field is a thunk, so call it.
((real-get x)))))))
(syntax-case s ()
((_ type syntactic-ctor ctor pred
(field get options ...) ...)
(let* ((field-spec #'((field get options ...) ...))
(thunked (filter-map thunked-field? field-spec))
(defaults (filter-map field-default-value
#'((field options ...) ...))))
(with-syntax (((field-spec* ...)
(map field-spec->srfi-9 field-spec))
((thunked-field-accessor ...)
(filter-map (lambda (field)
(and (thunked-field? field)
(thunked-field-accessor-definition
field)))
field-spec)))
#`(begin
(define-record-type type
(ctor field ...)
pred
field-spec* ...)
(begin thunked-field-accessor ...)
#,(make-syntactic-constructor #'type #'syntactic-ctor #'ctor
#'(field ...)
#:thunked thunked
#:defaults defaults))))))))
(define* (alist->record alist make keys
#:optional (multiple-value-keys '()))
"Apply MAKE to the values associated with KEYS in ALIST. Items in KEYS that
are also in MULTIPLE-VALUE-KEYS are considered to occur possibly multiple
times in ALIST, and thus their value is a list."
(let ((args (map (lambda (key)
(if (member key multiple-value-keys)
(filter-map (match-lambda
((k . v)
(and (equal? k key) v)))
alist)
(assoc-ref alist key)))
keys)))
(apply make args)))
(define (object->fields object fields port)
"Write OBJECT (typically a record) as a series of recutils-style fields to
PORT, according to FIELDS. FIELDS must be a list of field name/getter pairs."
(let loop ((fields fields))
(match fields
(()
object)
(((field . get) rest ...)
(format port "~a: ~a~%" field (get object))
(loop rest)))))
(define %recutils-field-charset
;; Valid characters starting a recutils field.
;; info "(recutils) Fields"
(char-set-union char-set:upper-case
char-set:lower-case
(char-set #\%)))
(define (recutils->alist port)
"Read a recutils-style record from PORT and return it as a list of key/value
pairs. Stop upon an empty line (after consuming it) or EOF."
(let loop ((line (read-line port))
(result '()))
(cond ((eof-object? line)
(reverse result))
((string-null? line)
(if (null? result)
(loop (read-line port) result) ; leading space: ignore it
(reverse result))) ; end-of-record marker
(else
;; Now check the first character of LINE, since that's what the
;; recutils manual says is enough.
(let ((first (string-ref line 0)))
(cond
((char-set-contains? %recutils-field-charset first)
(let* ((colon (string-index line #\:))
(field (string-take line colon))
(value (string-trim (string-drop line (+ 1 colon)))))
(loop (read-line port)
(alist-cons field value result))))
((eqv? first #\#) ;info "(recutils) Comments"
(loop (read-line port) result))
((eqv? first #\+) ;info "(recutils) Fields"
(let ((new-line (if (string-prefix? "+ " line)
(string-drop line 2)
(string-drop line 1))))
(match result
(((field . value) rest ...)
(loop (read-line port)
`((,field . ,(string-append value "\n" new-line))
,@rest))))))
(else
(error "unmatched line" line))))))))
;;; records.scm ends here