310b32a2a6
* guix/records.scm (make-syntactic-constructor): Add #:delayed
parameter.
[delayed-field?]: New procedure.
[wrap-field-value]: Use it.
(define-record-type*)[delayed-field?, wrapped-field?]: New procedures.
[thunked-field-accessor-name]: Rename to...
[wrapped-field-accessor-name]: ... this.
[field-spec->srfi-9]: Change 'thunked' to 'wrapped'.
[delayed-field-accessor-definition]: New procedure.
Compute delayed-field accessors and emit them. Pass #:delayed to
'make-syntactic-constructor'.
* tests/records.scm ("define-record-type* & delayed",
"define-record-type* & delayed & default",
"define-record-type* & delayed & inherited"): New tests.
354 lines
14 KiB
Scheme
354 lines
14 KiB
Scheme
;;; GNU Guix --- Functional package management for GNU
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;;; Copyright © 2012, 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
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;;;
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;;; This file is part of GNU Guix.
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;;;
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;;; GNU Guix is free software; you can redistribute it and/or modify it
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;;; under the terms of the GNU General Public License as published by
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;;; the Free Software Foundation; either version 3 of the License, or (at
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;;; your option) any later version.
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;;;
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;;; GNU Guix is distributed in the hope that it will be useful, but
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;;; WITHOUT ANY WARRANTY; without even the implied warranty of
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;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;;; GNU General Public License for more details.
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;;;
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;;; You should have received a copy of the GNU General Public License
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;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
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(define-module (guix records)
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#:use-module (srfi srfi-1)
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#:use-module (srfi srfi-9)
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#:use-module (srfi srfi-26)
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#:use-module (ice-9 match)
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#:use-module (ice-9 regex)
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#:use-module (ice-9 rdelim)
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#:export (define-record-type*
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alist->record
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object->fields
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recutils->alist))
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;;; Commentary:
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;;;
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;;; Utilities for dealing with Scheme records.
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;;;
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;;; Code:
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(define-syntax record-error
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(syntax-rules ()
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"Report a syntactic error in use of CONSTRUCTOR."
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((_ constructor form fmt args ...)
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(syntax-violation constructor
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(format #f fmt args ...)
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form))))
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(define* (make-syntactic-constructor type name ctor fields
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#:key (thunked '()) (defaults '())
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(delayed '()))
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"Make the syntactic constructor NAME for TYPE, that calls CTOR, and expects
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all of FIELDS to be initialized. DEFAULTS is the list of FIELD/DEFAULT-VALUE
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tuples, THUNKED is the list of identifiers of thunked fields, and DELAYED is
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the list of identifiers of delayed fields."
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(with-syntax ((type type)
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(name name)
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(ctor ctor)
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(expected fields)
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(defaults defaults))
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#`(define-syntax name
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(lambda (s)
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(define (record-inheritance orig-record field+value)
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;; Produce code that returns a record identical to ORIG-RECORD,
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;; except that values for the FIELD+VALUE alist prevail.
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(define (field-inherited-value f)
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(and=> (find (lambda (x)
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(eq? f (car (syntax->datum x))))
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field+value)
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car))
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;; Make sure there are no unknown field names.
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(let* ((fields (map (compose car syntax->datum) field+value))
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(unexpected (lset-difference eq? fields 'expected)))
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(when (pair? unexpected)
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(record-error 'name s "extraneous field initializers ~a"
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unexpected)))
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#`(make-struct type 0
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#,@(map (lambda (field index)
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(or (field-inherited-value field)
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#`(struct-ref #,orig-record
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#,index)))
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'expected
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(iota (length 'expected)))))
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(define (thunked-field? f)
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(memq (syntax->datum f) '#,thunked))
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(define (delayed-field? f)
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(memq (syntax->datum f) '#,delayed))
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(define (wrap-field-value f value)
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(cond ((thunked-field? f)
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#`(lambda () #,value))
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((delayed-field? f)
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#`(delay #,value))
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(else value)))
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(define (field-bindings field+value)
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;; Return field to value bindings, for use in 'let*' below.
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(map (lambda (field+value)
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(syntax-case field+value ()
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((field value)
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#`(field
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#,(wrap-field-value #'field #'value)))))
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field+value))
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(syntax-case s (inherit #,@fields)
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((_ (inherit orig-record) (field value) (... ...))
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#`(let* #,(field-bindings #'((field value) (... ...)))
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#,(record-inheritance #'orig-record
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#'((field value) (... ...)))))
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((_ (field value) (... ...))
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(let ((fields (map syntax->datum #'(field (... ...))))
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(dflt (map (match-lambda
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((f v)
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(list (syntax->datum f) v)))
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#'defaults)))
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(define (field-value f)
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(or (and=> (find (lambda (x)
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(eq? f (car (syntax->datum x))))
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#'((field value) (... ...)))
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car)
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(let ((value
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(car (assoc-ref dflt (syntax->datum f)))))
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(wrap-field-value f value))))
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(let ((fields (append fields (map car dflt))))
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(cond ((lset= eq? fields 'expected)
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#`(let* #,(field-bindings
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#'((field value) (... ...)))
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(ctor #,@(map field-value 'expected))))
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((pair? (lset-difference eq? fields 'expected))
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(record-error 'name s
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"extraneous field initializers ~a"
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(lset-difference eq? fields
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'expected)))
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(else
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(record-error 'name s
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"missing field initializers ~a"
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(lset-difference eq? 'expected
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fields))))))))))))
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(define-syntax define-record-type*
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(lambda (s)
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"Define the given record type such that an additional \"syntactic
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constructor\" is defined, which allows instances to be constructed with named
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field initializers, à la SRFI-35, as well as default values. An example use
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may look like this:
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(define-record-type* <thing> thing make-thing
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thing?
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(name thing-name (default \"chbouib\"))
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(port thing-port
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(default (current-output-port)) (thunked)))
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This example defines a macro 'thing' that can be used to instantiate records
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of this type:
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(thing
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(name \"foo\")
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(port (current-error-port)))
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The value of 'name' or 'port' could as well be omitted, in which case the
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default value specified in the 'define-record-type*' form is used:
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(thing)
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The 'port' field is \"thunked\", meaning that calls like '(thing-port x)' will
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actually compute the field's value in the current dynamic extent, which is
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useful when referring to fluids in a field's value.
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A field can also be marked as \"delayed\" instead of \"thunked\", in which
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case its value is effectively wrapped in a (delay …) form.
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It is possible to copy an object 'x' created with 'thing' like this:
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(thing (inherit x) (name \"bar\"))
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This expression returns a new object equal to 'x' except for its 'name'
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field."
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(define (field-default-value s)
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(syntax-case s (default)
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((field (default val) _ ...)
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(list #'field #'val))
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((field _ options ...)
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(field-default-value #'(field options ...)))
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(_ #f)))
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(define (delayed-field? s)
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;; Return the field name if the field defined by S is delayed.
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(syntax-case s (delayed)
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((field (delayed) _ ...)
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#'field)
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((field _ options ...)
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(delayed-field? #'(field options ...)))
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(_ #f)))
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(define (thunked-field? s)
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;; Return the field name if the field defined by S is thunked.
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(syntax-case s (thunked)
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((field (thunked) _ ...)
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#'field)
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((field _ options ...)
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(thunked-field? #'(field options ...)))
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(_ #f)))
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(define (wrapped-field? s)
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(or (thunked-field? s) (delayed-field? s)))
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(define (wrapped-field-accessor-name field)
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;; Return the name (an unhygienic syntax object) of the "real"
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;; getter for field, which is assumed to be a wrapped field.
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(syntax-case field ()
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((field get options ...)
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(let* ((getter (syntax->datum #'get))
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(real-getter (symbol-append '% getter '-real)))
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(datum->syntax #'get real-getter)))))
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(define (field-spec->srfi-9 field)
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;; Convert a field spec of our style to a SRFI-9 field spec of the
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;; form (field get).
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(syntax-case field ()
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((name get options ...)
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#`(name
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#,(if (wrapped-field? field)
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(wrapped-field-accessor-name field)
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#'get)))))
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(define (thunked-field-accessor-definition field)
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;; Return the real accessor for FIELD, which is assumed to be a
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;; thunked field.
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(syntax-case field ()
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((name get _ ...)
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(with-syntax ((real-get (wrapped-field-accessor-name field)))
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#'(define-inlinable (get x)
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;; The real value of that field is a thunk, so call it.
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((real-get x)))))))
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(define (delayed-field-accessor-definition field)
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;; Return the real accessor for FIELD, which is assumed to be a
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;; delayed field.
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(syntax-case field ()
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((name get _ ...)
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(with-syntax ((real-get (wrapped-field-accessor-name field)))
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#'(define-inlinable (get x)
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;; The real value of that field is a promise, so force it.
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(force (real-get x)))))))
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(syntax-case s ()
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((_ type syntactic-ctor ctor pred
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(field get options ...) ...)
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(let* ((field-spec #'((field get options ...) ...))
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(thunked (filter-map thunked-field? field-spec))
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(delayed (filter-map delayed-field? field-spec))
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(defaults (filter-map field-default-value
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#'((field options ...) ...))))
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(with-syntax (((field-spec* ...)
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(map field-spec->srfi-9 field-spec))
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((thunked-field-accessor ...)
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(filter-map (lambda (field)
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(and (thunked-field? field)
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(thunked-field-accessor-definition
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field)))
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field-spec))
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((delayed-field-accessor ...)
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(filter-map (lambda (field)
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(and (delayed-field? field)
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(delayed-field-accessor-definition
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field)))
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field-spec)))
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#`(begin
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(define-record-type type
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(ctor field ...)
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pred
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field-spec* ...)
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(begin thunked-field-accessor ...
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delayed-field-accessor ...)
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#,(make-syntactic-constructor #'type #'syntactic-ctor #'ctor
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#'(field ...)
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#:thunked thunked
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#:delayed delayed
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#:defaults defaults))))))))
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(define* (alist->record alist make keys
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#:optional (multiple-value-keys '()))
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"Apply MAKE to the values associated with KEYS in ALIST. Items in KEYS that
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are also in MULTIPLE-VALUE-KEYS are considered to occur possibly multiple
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times in ALIST, and thus their value is a list."
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(let ((args (map (lambda (key)
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(if (member key multiple-value-keys)
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(filter-map (match-lambda
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((k . v)
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(and (equal? k key) v)))
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alist)
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(assoc-ref alist key)))
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keys)))
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(apply make args)))
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(define (object->fields object fields port)
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"Write OBJECT (typically a record) as a series of recutils-style fields to
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PORT, according to FIELDS. FIELDS must be a list of field name/getter pairs."
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(let loop ((fields fields))
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(match fields
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(()
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object)
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(((field . get) rest ...)
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(format port "~a: ~a~%" field (get object))
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(loop rest)))))
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(define %recutils-field-charset
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;; Valid characters starting a recutils field.
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;; info "(recutils) Fields"
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(char-set-union char-set:upper-case
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char-set:lower-case
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(char-set #\%)))
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(define (recutils->alist port)
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"Read a recutils-style record from PORT and return it as a list of key/value
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pairs. Stop upon an empty line (after consuming it) or EOF."
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(let loop ((line (read-line port))
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(result '()))
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(cond ((eof-object? line)
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(reverse result))
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((string-null? line)
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(if (null? result)
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(loop (read-line port) result) ; leading space: ignore it
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(reverse result))) ; end-of-record marker
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(else
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;; Now check the first character of LINE, since that's what the
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;; recutils manual says is enough.
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(let ((first (string-ref line 0)))
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(cond
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((char-set-contains? %recutils-field-charset first)
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(let* ((colon (string-index line #\:))
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(field (string-take line colon))
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(value (string-trim (string-drop line (+ 1 colon)))))
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(loop (read-line port)
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(alist-cons field value result))))
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((eqv? first #\#) ;info "(recutils) Comments"
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(loop (read-line port) result))
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((eqv? first #\+) ;info "(recutils) Fields"
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(let ((new-line (if (string-prefix? "+ " line)
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(string-drop line 2)
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(string-drop line 1))))
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(match result
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(((field . value) rest ...)
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(loop (read-line port)
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`((,field . ,(string-append value "\n" new-line))
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,@rest))))))
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(else
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(error "unmatched line" line))))))))
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;;; records.scm ends here
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