501 lines
16 KiB
Scheme
501 lines
16 KiB
Scheme
;;; GNU Guix --- Functional package management for GNU
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;;; Copyright © 2013, 2014 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 monads)
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#:use-module (guix store)
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#:use-module (guix derivations)
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#:use-module (guix packages)
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#:use-module ((system syntax)
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#:select (syntax-local-binding))
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#:use-module (ice-9 match)
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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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#:export (;; Monads.
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define-monad
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monad?
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monad-bind
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monad-return
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;; Syntax.
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>>=
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return
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with-monad
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mlet
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mlet*
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mbegin
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mwhen
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munless
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lift0 lift1 lift2 lift3 lift4 lift5 lift6 lift7 lift
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listm
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foldm
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mapm
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sequence
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anym
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;; Concrete monads.
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%identity-monad
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%store-monad
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store-bind
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store-return
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store-lift
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run-with-store
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text-file
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text-file*
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interned-file
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package-file
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origin->derivation
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package->derivation
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package->cross-derivation
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built-derivations)
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#:replace (imported-modules
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compiled-modules))
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;;; Commentary:
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;;;
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;;; This module implements the general mechanism of monads, and provides in
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;;; particular an instance of the "store" monad. The API was inspired by that
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;;; of Racket's "better-monads" module (see
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;;; <http://planet.racket-lang.org/package-source/toups/functional.plt/1/1/planet-docs/better-monads-guide/index.html>).
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;;; The implementation and use case were influenced by Oleg Kysielov's
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;;; "Monadic Programming in Scheme" (see
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;;; <http://okmij.org/ftp/Scheme/monad-in-Scheme.html>).
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;;;
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;;; The store monad allows us to (1) build sequences of operations in the
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;;; store, and (2) make the store an implicit part of the execution context,
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;;; rather than a parameter of every single function.
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;;;
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;;; Code:
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;; Record type for monads manipulated at run time.
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(define-record-type <monad>
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(make-monad bind return)
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monad?
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(bind monad-bind)
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(return monad-return)) ; TODO: Add 'plus' and 'zero'
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(define-syntax define-monad
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(lambda (s)
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"Define the monad under NAME, with the given bind and return methods."
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(define prefix (string->symbol "% "))
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(define (make-rtd-name name)
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(datum->syntax name
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(symbol-append prefix (syntax->datum name) '-rtd)))
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(syntax-case s (bind return)
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((_ name (bind b) (return r))
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(with-syntax ((rtd (make-rtd-name #'name)))
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#`(begin
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(define rtd
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;; The record type, for use at run time.
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(make-monad b r))
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(define-syntax name
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;; An "inlined record", for use at expansion time. The goal is
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;; to allow 'bind' and 'return' to be resolved at expansion
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;; time, in the common case where the monad is accessed
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;; directly as NAME.
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(lambda (s)
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(syntax-case s (%bind %return)
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((_ %bind) #'b)
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((_ %return) #'r)
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(_ #'rtd))))))))))
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(define-syntax-parameter >>=
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;; The name 'bind' is already taken, so we choose this (obscure) symbol.
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(lambda (s)
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(syntax-violation '>>= ">>= (bind) used outside of 'with-monad'" s)))
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(define-syntax-parameter return
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(lambda (s)
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(syntax-violation 'return "return used outside of 'with-monad'" s)))
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(define-syntax with-monad
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(lambda (s)
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"Evaluate BODY in the context of MONAD, and return its result."
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(syntax-case s ()
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((_ monad body ...)
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(eq? 'macro (syntax-local-binding #'monad))
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;; MONAD is a syntax transformer, so we can obtain the bind and return
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;; methods by directly querying it.
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#'(syntax-parameterize ((>>= (identifier-syntax (monad %bind)))
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(return (identifier-syntax (monad %return))))
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body ...))
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((_ monad body ...)
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;; MONAD refers to the <monad> record that represents the monad at run
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;; time, so use the slow method.
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#'(syntax-parameterize ((>>= (identifier-syntax
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(monad-bind monad)))
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(return (identifier-syntax
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(monad-return monad))))
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body ...)))))
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(define-syntax mlet*
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(syntax-rules (->)
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"Bind the given monadic values MVAL to the given variables VAR. When the
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form is (VAR -> VAL), bind VAR to the non-monadic value VAL in the same way as
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'let'."
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;; Note: the '->' symbol corresponds to 'is:' in 'better-monads.rkt'.
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((_ monad () body ...)
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(with-monad monad body ...))
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((_ monad ((var mval) rest ...) body ...)
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(with-monad monad
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(>>= mval
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(lambda (var)
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(mlet* monad (rest ...)
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body ...)))))
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((_ monad ((var -> val) rest ...) body ...)
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(let ((var val))
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(mlet* monad (rest ...)
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body ...)))))
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(define-syntax mlet
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(lambda (s)
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(syntax-case s ()
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((_ monad ((var mval ...) ...) body ...)
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(with-syntax (((temp ...) (generate-temporaries #'(var ...))))
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#'(mlet* monad ((temp mval ...) ...)
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(let ((var temp) ...)
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body ...)))))))
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(define-syntax mbegin
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(syntax-rules (%current-monad)
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"Bind the given monadic expressions in sequence, returning the result of
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the last one."
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((_ %current-monad mexp)
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mexp)
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((_ %current-monad mexp rest ...)
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(>>= mexp
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(lambda (unused-value)
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(mbegin %current-monad rest ...))))
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((_ monad mexp)
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(with-monad monad
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mexp))
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((_ monad mexp rest ...)
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(with-monad monad
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(>>= mexp
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(lambda (unused-value)
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(mbegin monad rest ...)))))))
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(define-syntax mwhen
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(syntax-rules ()
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"When CONDITION is true, evaluate EXP0..EXP* as in an 'mbegin'. When
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CONDITION is false, return *unspecified* in the current monad."
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((_ condition exp0 exp* ...)
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(if condition
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(mbegin %current-monad
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exp0 exp* ...)
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(return *unspecified*)))))
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(define-syntax munless
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(syntax-rules ()
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"When CONDITION is false, evaluate EXP0..EXP* as in an 'mbegin'. When
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CONDITION is true, return *unspecified* in the current monad."
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((_ condition exp0 exp* ...)
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(if condition
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(return *unspecified*)
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(mbegin %current-monad
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exp0 exp* ...)))))
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(define-syntax define-lift
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(syntax-rules ()
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((_ liftn (args ...))
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(define (liftn proc monad)
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"Lift PROC to MONAD---i.e., return a monadic function in MONAD."
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(lambda (args ...)
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(with-monad monad
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(return (proc args ...))))))))
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(define-lift lift0 ())
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(define-lift lift1 (a))
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(define-lift lift2 (a b))
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(define-lift lift3 (a b c))
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(define-lift lift4 (a b c d))
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(define-lift lift5 (a b c d e))
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(define-lift lift6 (a b c d e f))
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(define-lift lift7 (a b c d e f g))
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(define (lift proc monad)
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"Lift PROC, a procedure that accepts an arbitrary number of arguments, to
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MONAD---i.e., return a monadic function in MONAD."
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(lambda args
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(with-monad monad
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(return (apply proc args)))))
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(define (foldm monad mproc init lst)
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"Fold MPROC over LST, a list of monadic values in MONAD, and return a
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monadic value seeded by INIT."
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(with-monad monad
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(let loop ((lst lst)
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(result init))
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(match lst
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(()
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(return result))
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((head tail ...)
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(mlet* monad ((item head)
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(result (mproc item result)))
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(loop tail result)))))))
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(define (mapm monad mproc lst)
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"Map MPROC over LST, a list of monadic values in MONAD, and return a monadic
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list. LST items are bound from left to right, so effects in MONAD are known
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to happen in that order."
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(mlet monad ((result (foldm monad
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(lambda (item result)
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(mlet monad ((item (mproc item)))
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(return (cons item result))))
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'()
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lst)))
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(return (reverse result))))
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(define-inlinable (sequence monad lst)
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"Turn the list of monadic values LST into a monadic list of values, by
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evaluating each item of LST in sequence."
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(with-monad monad
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(mapm monad return lst)))
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(define (anym monad proc lst)
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"Apply PROC to the list of monadic values LST; return the first value,
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lifted in MONAD, for which PROC returns true."
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(with-monad monad
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(let loop ((lst lst))
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(match lst
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(()
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(return #f))
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((head tail ...)
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(mlet* monad ((value head)
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(result -> (proc value)))
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(if result
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(return result)
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(loop tail))))))))
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(define-syntax listm
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(lambda (s)
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"Return a monadic list in MONAD from the monadic values MVAL."
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(syntax-case s ()
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((_ monad mval ...)
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(with-syntax (((val ...) (generate-temporaries #'(mval ...))))
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#'(mlet monad ((val mval) ...)
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(return (list val ...))))))))
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;;;
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;;; Identity monad.
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;;;
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(define-inlinable (identity-return value)
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value)
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(define-inlinable (identity-bind mvalue mproc)
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(mproc mvalue))
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(define-monad %identity-monad
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(bind identity-bind)
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(return identity-return))
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;;;
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;;; Store monad.
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;;;
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;; return:: a -> StoreM a
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(define-inlinable (store-return value)
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"Return VALUE from a monadic function."
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;; The monadic value is just this.
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(lambda (store)
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value))
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;; >>=:: StoreM a -> (a -> StoreM b) -> StoreM b
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(define-inlinable (store-bind mvalue mproc)
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"Bind MVALUE in MPROC."
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(lambda (store)
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(let* ((value (mvalue store))
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(mresult (mproc value)))
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(mresult store))))
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(define-monad %store-monad
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(bind store-bind)
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(return store-return))
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(define (store-lift proc)
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"Lift PROC, a procedure whose first argument is a connection to the store,
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in the store monad."
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(define result
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(lambda args
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(lambda (store)
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(apply proc store args))))
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(set-object-property! result 'documentation
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(procedure-property proc 'documentation))
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result)
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;;;
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;;; Store monad operators.
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;;;
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(define* (text-file name text)
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"Return as a monadic value the absolute file name in the store of the file
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containing TEXT, a string."
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(lambda (store)
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(add-text-to-store store name text '())))
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(define* (text-file* name #:rest text)
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"Return as a monadic value a derivation that builds a text file containing
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all of TEXT. TEXT may list, in addition to strings, packages, derivations,
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and store file names; the resulting store file holds references to all these."
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(define inputs
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;; Transform packages and derivations from TEXT into a valid input list.
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(filter-map (match-lambda
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((? package? p) `("x" ,p))
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((? derivation? d) `("x" ,d))
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((x ...) `("x" ,@x))
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((? string? s)
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(and (direct-store-path? s) `("x" ,s)))
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(x x))
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text))
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(define (computed-text text inputs)
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;; Using the lowered INPUTS, return TEXT with derivations replaced with
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;; their output file name.
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(define (real-string? s)
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(and (string? s) (not (direct-store-path? s))))
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(let loop ((inputs inputs)
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(text text)
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(result '()))
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(match text
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(()
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(string-concatenate-reverse result))
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(((? real-string? head) rest ...)
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(loop inputs rest (cons head result)))
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((_ rest ...)
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(match inputs
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(((_ (? derivation? drv) sub-drv ...) inputs ...)
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(loop inputs rest
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(cons (apply derivation->output-path drv
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sub-drv)
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result)))
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(((_ file) inputs ...)
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;; FILE is the result of 'add-text-to-store' or so.
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(loop inputs rest (cons file result))))))))
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(define (builder inputs)
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`(call-with-output-file (assoc-ref %outputs "out")
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(lambda (port)
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(display ,(computed-text text inputs) port))))
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;; TODO: Rewrite using 'gexp->derivation'.
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(mlet %store-monad ((inputs (lower-inputs inputs)))
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(derivation-expression name (builder inputs)
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#:inputs inputs)))
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(define* (interned-file file #:optional name
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#:key (recursive? #t))
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"Return the name of FILE once interned in the store. Use NAME as its store
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name, or the basename of FILE if NAME is omitted.
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When RECURSIVE? is true, the contents of FILE are added recursively; if FILE
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designates a flat file and RECURSIVE? is true, its contents are added, and its
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permission bits are kept."
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(lambda (store)
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(add-to-store store (or name (basename file))
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recursive? "sha256" file)))
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(define* (package-file package
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#:optional file
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#:key
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system (output "out") target)
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"Return as a monadic value the absolute file name of FILE within the
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OUTPUT directory of PACKAGE. When FILE is omitted, return the name of the
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OUTPUT directory of PACKAGE. When TARGET is true, use it as a
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cross-compilation target triplet."
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(lambda (store)
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(define compute-derivation
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(if target
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(cut package-cross-derivation <> <> target <>)
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package-derivation))
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(let* ((system (or system (%current-system)))
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(drv (compute-derivation store package system))
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(out (derivation->output-path drv output)))
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(if file
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(string-append out "/" file)
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out))))
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(define (lower-inputs inputs)
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"Turn any package from INPUTS into a derivation; return the corresponding
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input list as a monadic value."
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;; XXX: This procedure is bound to disappear with 'derivation-expression'.
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(with-monad %store-monad
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(sequence %store-monad
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(map (match-lambda
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((name (? package? package) sub-drv ...)
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(mlet %store-monad ((drv (package->derivation package)))
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(return `(,name ,drv ,@sub-drv))))
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((name (? string? file))
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(return `(,name ,file)))
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(tuple
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(return tuple)))
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inputs))))
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(define derivation-expression
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;; XXX: This procedure is superseded by 'gexp->derivation'.
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(store-lift build-expression->derivation))
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(define package->derivation
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(store-lift package-derivation))
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(define package->cross-derivation
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(store-lift package-cross-derivation))
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(define origin->derivation
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(store-lift package-source-derivation))
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(define imported-modules
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(store-lift (@ (guix derivations) imported-modules)))
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(define compiled-modules
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(store-lift (@ (guix derivations) compiled-modules)))
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(define built-derivations
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(store-lift build-derivations))
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(define* (run-with-store store mval
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#:key
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(guile-for-build (%guile-for-build))
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(system (%current-system)))
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"Run MVAL, a monadic value in the store monad, in STORE, an open store
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connection."
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(define (default-guile)
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;; Lazily resolve 'guile-final'. This module must not refer to (gnu …)
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;; modules directly, to avoid circular dependencies, hence this hack.
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(module-ref (resolve-interface '(gnu packages commencement))
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'guile-final))
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(parameterize ((%guile-for-build (or guile-for-build
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(package-derivation store
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(default-guile)
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system)))
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(%current-system system))
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(mval store)))
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;;; monads.scm end here
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