Mirror of GNU Guix
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;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2013, 2014 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
;;; 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 monads)
#:use-module (guix store)
#:use-module (guix derivations)
#:use-module (guix packages)
#:use-module ((system syntax)
#:select (syntax-local-binding))
#:use-module (ice-9 match)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-9)
#:use-module (srfi srfi-26)
#:export (;; Monads.
;; Syntax.
lift1 lift2 lift3 lift4 lift5 lift6 lift7 lift
;; Concrete monads.
#:replace (imported-modules
;;; Commentary:
;;; This module implements the general mechanism of monads, and provides in
;;; particular an instance of the "store" monad. The API was inspired by that
;;; of Racket's "better-monads" module (see
;;; <http://planet.racket-lang.org/package-source/toups/functional.plt/1/1/planet-docs/better-monads-guide/index.html>).
;;; The implementation and use case were influenced by Oleg Kysielov's
;;; "Monadic Programming in Scheme" (see
;;; <http://okmij.org/ftp/Scheme/monad-in-Scheme.html>).
;;; The store monad allows us to (1) build sequences of operations in the
;;; store, and (2) make the store an implicit part of the execution context,
;;; rather than a parameter of every single function.
;;; Code:
;; Record type for monads manipulated at run time.
(define-record-type <monad>
(make-monad bind return)
(bind monad-bind)
(return monad-return)) ; TODO: Add 'plus' and 'zero'
(define-syntax define-monad
(lambda (s)
"Define the monad under NAME, with the given bind and return methods."
(define prefix (string->symbol "% "))
(define (make-rtd-name name)
(datum->syntax name
(symbol-append prefix (syntax->datum name) '-rtd)))
(syntax-case s (bind return)
((_ name (bind b) (return r))
(with-syntax ((rtd (make-rtd-name #'name)))
(define rtd
;; The record type, for use at run time.
(make-monad b r))
(define-syntax name
;; An "inlined record", for use at expansion time. The goal is
;; to allow 'bind' and 'return' to be resolved at expansion
;; time, in the common case where the monad is accessed
;; directly as NAME.
(lambda (s)
(syntax-case s (%bind %return)
((_ %bind) #'b)
((_ %return) #'r)
(_ #'rtd))))))))))
(define-syntax-parameter >>=
;; The name 'bind' is already taken, so we choose this (obscure) symbol.
(lambda (s)
(syntax-violation '>>= ">>= (bind) used outside of 'with-monad'" s)))
(define-syntax-parameter return
(lambda (s)
(syntax-violation 'return "return used outside of 'with-monad'" s)))
(define-syntax with-monad
(lambda (s)
"Evaluate BODY in the context of MONAD, and return its result."
(syntax-case s ()
((_ monad body ...)
(eq? 'macro (syntax-local-binding #'monad))
;; MONAD is a syntax transformer, so we can obtain the bind and return
;; methods by directly querying it.
#'(syntax-parameterize ((>>= (identifier-syntax (monad %bind)))
(return (identifier-syntax (monad %return))))
body ...))
((_ monad body ...)
;; MONAD refers to the <monad> record that represents the monad at run
;; time, so use the slow method.
#'(syntax-parameterize ((>>= (identifier-syntax
(monad-bind monad)))
(return (identifier-syntax
(monad-return monad))))
body ...)))))
(define-syntax mlet*
(syntax-rules (->)
"Bind the given monadic values MVAL to the given variables VAR. When the
form is (VAR -> VAL), bind VAR to the non-monadic value VAL in the same way as
;; Note: the '->' symbol corresponds to 'is:' in 'better-monads.rkt'.
((_ monad () body ...)
(with-monad monad body ...))
((_ monad ((var mval) rest ...) body ...)
(with-monad monad
(>>= mval
(lambda (var)
(mlet* monad (rest ...)
body ...)))))
((_ monad ((var -> val) rest ...) body ...)
(let ((var val))
(mlet* monad (rest ...)
body ...)))))
(define-syntax mlet
(lambda (s)
(syntax-case s ()
((_ monad ((var mval ...) ...) body ...)
(with-syntax (((temp ...) (generate-temporaries #'(var ...))))
#'(mlet* monad ((temp mval ...) ...)
(let ((var temp) ...)
body ...)))))))
(define-syntax define-lift
(syntax-rules ()
((_ liftn (args ...))
(define (liftn proc monad)
"Lift PROC to MONAD---i.e., return a monadic function in MONAD."
(lambda (args ...)
(with-monad monad
(return (proc args ...))))))))
(define-lift lift1 (a))
(define-lift lift2 (a b))
(define-lift lift3 (a b c))
(define-lift lift4 (a b c d))
(define-lift lift5 (a b c d e))
(define-lift lift6 (a b c d e f))
(define-lift lift7 (a b c d e f g))
(define (lift nargs proc monad)
"Lift PROC, a procedure that accepts NARGS arguments, to MONAD---i.e.,
return a monadic function in MONAD."
(lambda args
(with-monad monad
(return (apply proc args)))))
(define (foldm monad mproc init lst)
"Fold MPROC over LST, a list of monadic values in MONAD, and return a
monadic value seeded by INIT."
(with-monad monad
(let loop ((lst lst)
(result init))
(match lst
(return result))
((head tail ...)
(mlet* monad ((item head)
(result (mproc item result)))
(loop tail result)))))))
(define (mapm monad mproc lst)
"Map MPROC over LST, a list of monadic values in MONAD, and return a monadic
(foldm monad
(lambda (item result)
(mlet monad ((item (mproc item)))
(return (cons item result))))
(reverse lst)))
(define-inlinable (sequence monad lst)
"Turn the list of monadic values LST into a monadic list of values, by
evaluating each item of LST in sequence."
(with-monad monad
(mapm monad return lst)))
(define (anym monad proc lst)
"Apply PROC to the list of monadic values LST; return the first value,
lifted in MONAD, for which PROC returns true."
(with-monad monad
(let loop ((lst lst))
(match lst
(return #f))
((head tail ...)
(mlet* monad ((value head)
(result -> (proc value)))
(if result
(return result)
(loop tail))))))))
(define-syntax listm
(lambda (s)
"Return a monadic list in MONAD from the monadic values MVAL."
(syntax-case s ()
((_ monad mval ...)
(with-syntax (((val ...) (generate-temporaries #'(mval ...))))
#'(mlet monad ((val mval) ...)
(return (list val ...))))))))
;;; Identity monad.
(define-inlinable (identity-return value)
(define-inlinable (identity-bind mvalue mproc)
(mproc mvalue))
(define-monad %identity-monad
(bind identity-bind)
(return identity-return))
;;; Store monad.
;; return:: a -> StoreM a
(define-inlinable (store-return value)
"Return VALUE from a monadic function."
;; The monadic value is just this.
(lambda (store)
;; >>=:: StoreM a -> (a -> StoreM b) -> StoreM b
(define-inlinable (store-bind mvalue mproc)
(lambda (store)
(let* ((value (mvalue store))
(mresult (mproc value)))
(mresult store))))
(define-monad %store-monad
(bind store-bind)
(return store-return))
(define (store-lift proc)
"Lift PROC, a procedure whose first argument is a connection to the store,
in the store monad."
(define result
(lambda args
(lambda (store)
(apply proc store args))))
(set-object-property! result 'documentation
(procedure-property proc 'documentation))
;;; Store monad operators.
(define* (text-file name text)
"Return as a monadic value the absolute file name in the store of the file
containing TEXT, a string."
(lambda (store)
(add-text-to-store store name text '())))
(define* (text-file* name #:rest text)
"Return as a monadic value a derivation that builds a text file containing
all of TEXT. TEXT may list, in addition to strings, packages, derivations,
and store file names; the resulting store file holds references to all these."
(define inputs
;; Transform packages and derivations from TEXT into a valid input list.
(filter-map (match-lambda
((? package? p) `("x" ,p))
((? derivation? d) `("x" ,d))
((x ...) `("x" ,@x))
((? string? s)
(and (direct-store-path? s) `("x" ,s)))
(x x))
(define (computed-text text inputs)
;; Using the lowered INPUTS, return TEXT with derivations replaced with
;; their output file name.
(define (real-string? s)
(and (string? s) (not (direct-store-path? s))))
(let loop ((inputs inputs)
(text text)
(result '()))
(match text
(string-concatenate-reverse result))
(((? real-string? head) rest ...)
(loop inputs rest (cons head result)))
((_ rest ...)
(match inputs
(((_ (? derivation? drv) sub-drv ...) inputs ...)
(loop inputs rest
(cons (apply derivation->output-path drv
(((_ file) inputs ...)
;; FILE is the result of 'add-text-to-store' or so.
(loop inputs rest (cons file result))))))))
(define (builder inputs)
`(call-with-output-file (assoc-ref %outputs "out")
(lambda (port)
(display ,(computed-text text inputs) port))))
;; TODO: Rewrite using 'gexp->derivation'.
(mlet %store-monad ((inputs (lower-inputs inputs)))
(derivation-expression name (builder inputs)
#:inputs inputs)))
(define* (package-file package
#:optional file
#:key (system (%current-system)) (output "out"))
"Return as a monadic value the absolute file name of FILE within the
OUTPUT directory of PACKAGE. When FILE is omitted, return the name of the
OUTPUT directory of PACKAGE."
(lambda (store)
(let* ((drv (package-derivation store package system))
(out (derivation->output-path drv output)))
(if file
(string-append out "/" file)
(define (lower-inputs inputs)
"Turn any package from INPUTS into a derivation; return the corresponding
input list as a monadic value."
;; XXX: This procedure is bound to disappear with 'derivation-expression'.
(with-monad %store-monad
(sequence %store-monad
(map (match-lambda
((name (? package? package) sub-drv ...)
(mlet %store-monad ((drv (package->derivation package)))
(return `(,name ,drv ,@sub-drv))))
((name (? string? file))
(return `(,name ,file)))
(return tuple)))
(define derivation-expression
;; XXX: This procedure is superseded by 'gexp->derivation'.
(store-lift build-expression->derivation))
(define package->derivation
(store-lift package-derivation))
(define origin->derivation
(store-lift package-source-derivation))
(define imported-modules
(store-lift (@ (guix derivations) imported-modules)))
(define compiled-modules
(store-lift (@ (guix derivations) compiled-modules)))
(define built-derivations
(store-lift build-derivations))
(define* (run-with-store store mval
(guile-for-build (%guile-for-build))
(system (%current-system)))
"Run MVAL, a monadic value in the store monad, in STORE, an open store
(define (default-guile)
;; Lazily resolve 'guile-final'. This module must not refer to (gnu …)
;; modules directly, to avoid circular dependencies, hence this hack.
(module-ref (resolve-interface '(gnu packages base))
(parameterize ((%guile-for-build (or guile-for-build
(package-derivation store
(%current-system system))
(mval store)))
;;; monads.scm end here