[jackhill/guix/guix.git] / guix / records.scm

;;; 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* (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 (wrap-field-value f value)
            (if (thunked-field? f)
                #`(lambda () #,value)
                value))

          (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
                         #,(wrap-field-value #'field #'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)))))
                       (wrap-field-value f 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-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 (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
Commit	Line	Data
c0cd1b3e	1	;;; GNU Guix --- Functional package management for GNU
fb519bd8	2	;;; Copyright © 2012, 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
c0cd1b3e LC	3	;;;
	4	;;; This file is part of GNU Guix.
	5	;;;
	6	;;; GNU Guix is free software; you can redistribute it and/or modify it
	7	;;; under the terms of the GNU General Public License as published by
	8	;;; the Free Software Foundation; either version 3 of the License, or (at
	9	;;; your option) any later version.
	10	;;;
	11	;;; GNU Guix is distributed in the hope that it will be useful, but
	12	;;; WITHOUT ANY WARRANTY; without even the implied warranty of
	13	;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	14	;;; GNU General Public License for more details.
	15	;;;
	16	;;; You should have received a copy of the GNU General Public License
	17	;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
	18
	19	(define-module (guix records)
	20	#:use-module (srfi srfi-1)
	21	#:use-module (srfi srfi-9)
	22	#:use-module (srfi srfi-26)
	23	#:use-module (ice-9 match)
fdc1bf65 LC	24	#:use-module (ice-9 regex)
fdc1bf65 LC	25	#:use-module (ice-9 rdelim)
c0cd1b3e LC	26	#:export (define-record-type*
c0cd1b3e LC	27	alist->record
fdc1bf65 LC	28	object->fields
fdc1bf65 LC	29	recutils->alist))
c0cd1b3e LC	30
	31	;;; Commentary:
	32	;;;
	33	;;; Utilities for dealing with Scheme records.
	34	;;;
	35	;;; Code:
	36
b1353e7a LC	37	(define-syntax record-error
	38	(syntax-rules ()
	39	"Report a syntactic error in use of CONSTRUCTOR."
	40	((_ constructor form fmt args ...)
	41	(syntax-violation constructor
	42	(format #f fmt args ...)
	43	form))))
	44
cf4efb39	45	(define* (make-syntactic-constructor type name ctor fields
0db40ed2	46	#:key (thunked '()) (defaults '()))
cf4efb39 LC	47	"Make the syntactic constructor NAME for TYPE, that calls CTOR, and expects
	48	all of FIELDS to be initialized. DEFAULTS is the list of FIELD/DEFAULT-VALUE
	49	tuples, and THUNKED is the list of identifiers of thunked fields."
	50	(with-syntax ((type type)
	51	(name name)
	52	(ctor ctor)
	53	(expected fields)
	54	(defaults defaults))
	55	#`(define-syntax name
	56	(lambda (s)
	57	(define (record-inheritance orig-record field+value)
	58	;; Produce code that returns a record identical to ORIG-RECORD,
	59	;; except that values for the FIELD+VALUE alist prevail.
	60	(define (field-inherited-value f)
	61	(and=> (find (lambda (x)
	62	(eq? f (car (syntax->datum x))))
	63	field+value)
	64	car))
	65
	66	;; Make sure there are no unknown field names.
	67	(let* ((fields (map (compose car syntax->datum) field+value))
	68	(unexpected (lset-difference eq? fields 'expected)))
	69	(when (pair? unexpected)
	70	(record-error 'name s "extraneous field initializers ~a"
	71	unexpected)))
	72
	73	#`(make-struct type 0
	74	#,@(map (lambda (field index)
	75	(or (field-inherited-value field)
	76	#`(struct-ref #,orig-record
	77	#,index)))
	78	'expected
	79	(iota (length 'expected)))))
	80
	81	(define (thunked-field? f)
	82	(memq (syntax->datum f) '#,thunked))
	83
c492be65 LC	84	(define (wrap-field-value f value)
	85	(if (thunked-field? f)
	86	#`(lambda () #,value)
	87	value))
	88
cf4efb39 LC	89	(define (field-bindings field+value)
	90	;; Return field to value bindings, for use in 'let*' below.
	91	(map (lambda (field+value)
	92	(syntax-case field+value ()
	93	((field value)
	94	#`(field
c492be65	95	#,(wrap-field-value #'field #'value)))))
cf4efb39 LC	96	field+value))
	97
	98	(syntax-case s (inherit #,@fields)
	99	((_ (inherit orig-record) (field value) (... ...))
	100	#`(let* #,(field-bindings #'((field value) (... ...)))
	101	#,(record-inheritance #'orig-record
	102	#'((field value) (... ...)))))
	103	((_ (field value) (... ...))
	104	(let ((fields (map syntax->datum #'(field (... ...))))
	105	(dflt (map (match-lambda
	106	((f v)
	107	(list (syntax->datum f) v)))
	108	#'defaults)))
	109
	110	(define (field-value f)
	111	(or (and=> (find (lambda (x)
	112	(eq? f (car (syntax->datum x))))
	113	#'((field value) (... ...)))
	114	car)
	115	(let ((value
	116	(car (assoc-ref dflt (syntax->datum f)))))
c492be65	117	(wrap-field-value f value))))
cf4efb39 LC	118
	119	(let ((fields (append fields (map car dflt))))
	120	(cond ((lset= eq? fields 'expected)
	121	#`(let* #,(field-bindings
	122	#'((field value) (... ...)))
	123	(ctor #,@(map field-value 'expected))))
	124	((pair? (lset-difference eq? fields 'expected))
	125	(record-error 'name s
	126	"extraneous field initializers ~a"
	127	(lset-difference eq? fields
	128	'expected)))
	129	(else
	130	(record-error 'name s
	131	"missing field initializers ~a"
	132	(lset-difference eq? 'expected
	133	fields))))))))))))
	134
c0cd1b3e LC	135	(define-syntax define-record-type*
	136	(lambda (s)
	137	"Define the given record type such that an additional \"syntactic
	138	constructor\" is defined, which allows instances to be constructed with named
e2540884 LC	139	field initializers, à la SRFI-35, as well as default values. An example use
	140	may look like this:
	141
	142	(define-record-type* <thing> thing make-thing
	143	thing?
	144	(name thing-name (default \"chbouib\"))
	145	(port thing-port
	146	(default (current-output-port)) (thunked)))
	147
	148	This example defines a macro 'thing' that can be used to instantiate records
	149	of this type:
	150
	151	(thing
	152	(name \"foo\")
	153	(port (current-error-port)))
	154
	155	The value of 'name' or 'port' could as well be omitted, in which case the
	156	default value specified in the 'define-record-type*' form is used:
	157
	158	(thing)
	159
	160	The 'port' field is \"thunked\", meaning that calls like '(thing-port x)' will
	161	actually compute the field's value in the current dynamic extent, which is
	162	useful when referring to fluids in a field's value.
	163
	164	It is possible to copy an object 'x' created with 'thing' like this:
	165
	166	(thing (inherit x) (name \"bar\"))
	167
	168	This expression returns a new object equal to 'x' except for its 'name'
	169	field."
	170
c0cd1b3e LC	171	(define (field-default-value s)
	172	(syntax-case s (default)
	173	((field (default val) _ ...)
	174	(list #'field #'val))
	175	((field _ options ...)
	176	(field-default-value #'(field options ...)))
	177	(_ #f)))
	178
	179	(define (thunked-field? s)
	180	;; Return the field name if the field defined by S is thunked.
	181	(syntax-case s (thunked)
	182	((field (thunked) _ ...)
	183	#'field)
	184	((field _ options ...)
	185	(thunked-field? #'(field options ...)))
	186	(_ #f)))
	187
	188	(define (thunked-field-accessor-name field)
	189	;; Return the name (an unhygienic syntax object) of the "real"
	190	;; getter for field, which is assumed to be a thunked field.
	191	(syntax-case field ()
	192	((field get options ...)
	193	(let* ((getter (syntax->datum #'get))
	194	(real-getter (symbol-append '% getter '-real)))
	195	(datum->syntax #'get real-getter)))))
	196
	197	(define (field-spec->srfi-9 field)
	198	;; Convert a field spec of our style to a SRFI-9 field spec of the
	199	;; form (field get).
	200	(syntax-case field ()
	201	((name get options ...)
	202	#`(name
	203	#,(if (thunked-field? field)
	204	(thunked-field-accessor-name field)
	205	#'get)))))
	206
	207	(define (thunked-field-accessor-definition field)
	208	;; Return the real accessor for FIELD, which is assumed to be a
	209	;; thunked field.
	210	(syntax-case field ()
	211	((name get _ ...)
	212	(with-syntax ((real-get (thunked-field-accessor-name field)))
	213	#'(define-inlinable (get x)
	214	;; The real value of that field is a thunk, so call it.
	215	((real-get x)))))))
	216
	217	(syntax-case s ()
	218	((_ type syntactic-ctor ctor pred
	219	(field get options ...) ...)
9b543456 LC	220	(let* ((field-spec #'((field get options ...) ...))
	221	(thunked (filter-map thunked-field? field-spec))
	222	(defaults (filter-map field-default-value
	223	#'((field options ...) ...))))
c0cd1b3e LC	224	(with-syntax (((field-spec* ...)
	225	(map field-spec->srfi-9 field-spec))
	226	((thunked-field-accessor ...)
	227	(filter-map (lambda (field)
	228	(and (thunked-field? field)
	229	(thunked-field-accessor-definition
	230	field)))
	231	field-spec)))
	232	#`(begin
	233	(define-record-type type
	234	(ctor field ...)
	235	pred
	236	field-spec* ...)
	237	(begin thunked-field-accessor ...)
	238	#,(make-syntactic-constructor #'type #'syntactic-ctor #'ctor
	239	#'(field ...)
9b543456 LC	240	#:thunked thunked
9b543456 LC	241	#:defaults defaults))))))))
c0cd1b3e	242
c8772a7a LC	243	(define* (alist->record alist make keys
	244	#:optional (multiple-value-keys '()))
	245	"Apply MAKE to the values associated with KEYS in ALIST. Items in KEYS that
	246	are also in MULTIPLE-VALUE-KEYS are considered to occur possibly multiple
	247	times in ALIST, and thus their value is a list."
	248	(let ((args (map (lambda (key)
	249	(if (member key multiple-value-keys)
	250	(filter-map (match-lambda
	251	((k . v)
	252	(and (equal? k key) v)))
	253	alist)
	254	(assoc-ref alist key)))
	255	keys)))
c0cd1b3e LC	256	(apply make args)))
	257
	258	(define (object->fields object fields port)
	259	"Write OBJECT (typically a record) as a series of recutils-style fields to
	260	PORT, according to FIELDS. FIELDS must be a list of field name/getter pairs."
	261	(let loop ((fields fields))
	262	(match fields
	263	(()
	264	object)
	265	(((field . get) rest ...)
	266	(format port "~a: ~a~%" field (get object))
	267	(loop rest)))))
	268
fb519bd8 LC	269	(define %recutils-field-charset
	270	;; Valid characters starting a recutils field.
	271	;; info "(recutils) Fields"
	272	(char-set-union char-set:upper-case
	273	char-set:lower-case
	274	(char-set #\%)))
836d10f1	275
fdc1bf65 LC	276	(define (recutils->alist port)
	277	"Read a recutils-style record from PORT and return it as a list of key/value
	278	pairs. Stop upon an empty line (after consuming it) or EOF."
	279	(let loop ((line (read-line port))
	280	(result '()))
b7b88288	281	(cond ((eof-object? line)
fdc1bf65	282	(reverse result))
b7b88288 LC	283	((string-null? line)
	284	(if (null? result)
	285	(loop (read-line port) result) ; leading space: ignore it
	286	(reverse result))) ; end-of-record marker
fdc1bf65	287	(else
fb519bd8 LC	288	;; Now check the first character of LINE, since that's what the
	289	;; recutils manual says is enough.
	290	(let ((first (string-ref line 0)))
	291	(cond
	292	((char-set-contains? %recutils-field-charset first)
	293	(let* ((colon (string-index line #\:))
	294	(field (string-take line colon))
	295	(value (string-trim (string-drop line (+ 1 colon)))))
	296	(loop (read-line port)
	297	(alist-cons field value result))))
	298	((eqv? first #\#) ;info "(recutils) Comments"
	299	(loop (read-line port) result))
	300	((eqv? first #\+) ;info "(recutils) Fields"
	301	(let ((new-line (if (string-prefix? "+ " line)
	302	(string-drop line 2)
	303	(string-drop line 1))))
	304	(match result
	305	(((field . value) rest ...)
	306	(loop (read-line port)
	307	`((,field . ,(string-append value "\n" new-line))
	308	,@rest))))))
	309	(else
	310	(error "unmatched line" line))))))))
fdc1bf65	311
c0cd1b3e	312	;;; records.scm ends here