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Add (guix monads).
Add (guix monads).
* guix/monads.scm: New file. * tests/monads.scm: New file. * Makefile.am (MODULES): Add guix/monads.scm. (SCM_TESTS): Add tests/monads.scm. * doc/guix.texi (The Store Monad): New node. (The Store): Reference it.gn-latest-20200428
Ludovic Courtès
8 years ago
5 changed files with 624 additions and 4 deletions
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8.dir-locals.el
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2Makefile.am
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149doc/guix.texi
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306guix/monads.scm
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163tests/monads.scm
@ -0,0 +1,306 @@ |
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;;; GNU Guix --- Functional package management for GNU |
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;;; Copyright © 2013 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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|
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(define-module (guix monads) |
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#:use-module (guix records) |
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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 (ice-9 match) |
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#:use-module (srfi srfi-26) |
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#:export (;; Monads. |
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monad |
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monad? |
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monad-bind |
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monad-return |
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|
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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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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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|
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;; Concrete monads. |
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%identity-monad |
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|
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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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package-file |
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package->derivation |
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built-derivations |
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derivation-expression)) |
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|
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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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|
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(define-record-type* <monad> monad make-monad |
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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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|
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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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|
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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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|
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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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#'(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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|
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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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|
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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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|
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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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|
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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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|
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(define (lift nargs proc monad) |
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"Lift PROC, a procedure that accepts NARGS arguments, to MONAD---i.e., |
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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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|
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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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|
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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." |
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(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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(reverse lst))) |
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|
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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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;; FIXME: 'mapm' binds from right to left. |
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(with-monad monad |
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(mapm monad return lst))) |
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|
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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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(or (and=> (proc value) return) |
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head |
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(loop tail)))))))) |
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|
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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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|
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|
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;;; |
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;;; Identity monad. |
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;;; |
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|
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(define (identity-return value) |
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value) |
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|
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(define (identity-bind mvalue mproc) |
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(mproc mvalue)) |
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|
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(define %identity-monad |
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(monad |
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(bind identity-bind) |
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(return identity-return))) |
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|
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|
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;;; |
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;;; Store monad. |
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;;; |
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|
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;; return:: a -> StoreM a |
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(define (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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|
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;; >>=:: StoreM a -> (a -> StoreM b) -> StoreM b |
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(define (store-bind mvalue 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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|
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(define %store-monad |
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(monad |
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(return store-return) |
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(bind store-bind))) |
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|
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|
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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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|
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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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;;; |
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;;; Store monad operators. |
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;;; |
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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." |
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(lambda (store) |
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(add-text-to-store store name text '()))) |
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|
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(define* (package-file package |
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#:optional file |
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#:key (system (%current-system)) (output "out")) |
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"Return as a monadic value in 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." |
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(lambda (store) |
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(let* ((drv (package-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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|
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(define derivation-expression |
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(store-lift build-expression->derivation)) |
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|
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(define package->derivation |
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(store-lift package-derivation)) |
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|
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(define built-derivations |
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(store-lift build-derivations)) |
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|
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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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(parameterize ((%guile-for-build (or guile-for-build |
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(package-derivation store |
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(@ (gnu packages base) |
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guile-final) |
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system))) |
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(%current-system system)) |
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(mval store))) |
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|
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;;; monads.scm end here |
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@ -0,0 +1,163 @@ |
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;;; GNU Guix --- Functional package management for GNU |
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;;; Copyright © 2013 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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|
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(define-module (test-monads) |
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#:use-module (guix store) |
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#:use-module (guix monads) |
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#:use-module (guix derivations) |
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#:use-module ((guix packages) |
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#:select (package-derivation %current-system)) |
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#:use-module (gnu packages) |
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#:use-module (gnu packages bootstrap) |
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#:use-module (ice-9 match) |
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#:use-module (rnrs io ports) |
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#:use-module (srfi srfi-1) |
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#:use-module (srfi srfi-26) |
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#:use-module (srfi srfi-64)) |
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|
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;; Test the (guix store) module. |
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|
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(define %store |
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(open-connection)) |
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|
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;; Make sure we build everything by ourselves. |
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(set-build-options %store #:use-substitutes? #f) |
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|
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(define %monads |
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(list %identity-monad %store-monad)) |
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|
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(define %monad-run |
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(list identity |
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(cut run-with-store %store <>))) |
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|
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|
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(test-begin "monads") |
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|
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;; The 3 "monad laws": <http://www.haskell.org/haskellwiki/Monad_laws>. |
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|
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(test-assert "left identity" |
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(every (lambda (monad run) |
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(let ((number (random 777))) |
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(with-monad monad |
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(define (f x) |
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(return (* (1+ number) 2))) |
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|
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(= (run (>>= (return number) f)) |
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(run (f number)))))) |
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%monads |
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%monad-run)) |
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|
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(test-assert "right identity" |
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(every (lambda (monad run) |
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(with-monad monad |
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(let ((number (return (random 777)))) |
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(= (run (>>= number return)) |
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(run number))))) |
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%monads |
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%monad-run)) |
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|
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(test-assert "associativity" |
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(every (lambda (monad run) |
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(with-monad monad |
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(define (f x) |
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(return (+ 1 x))) |
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(define (g x) |
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(return (* 2 x))) |
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|
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(let ((number (return (random 777)))) |
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(= (run (>>= (>>= number f) g)) |
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(run (>>= number (lambda (x) (>>= (f x) g)))))))) |
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%monads |
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%monad-run)) |
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|
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(test-assert "lift" |
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(every (lambda (monad run) |
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(let ((f (lift1 1+ monad))) |
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(with-monad monad |
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(let ((number (random 777))) |
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(= (run (>>= (return number) f)) |
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(1+ number)))))) |
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%monads |
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%monad-run)) |
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|
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(test-assert "mlet* + text-file + package-file" |
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(run-with-store %store |
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(mlet* %store-monad ((guile (package-file %bootstrap-guile "bin/guile")) |
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(file (text-file "monadic" guile))) |
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(return (equal? (call-with-input-file file get-string-all) |
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guile))) |
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#:guile-for-build (package-derivation %store %bootstrap-guile))) |
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|
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(test-assert "mlet* + derivation-expression" |
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(run-with-store %store |
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(mlet* %store-monad ((guile (package-file %bootstrap-guile "bin/guile")) |
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(gdrv (package->derivation %bootstrap-guile)) |
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(exp -> `(let ((out (assoc-ref %outputs "out"))) |
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(mkdir out) |
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(symlink ,guile |
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(string-append out "/guile-rocks")))) |
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(drv (derivation-expression "rocks" (%current-system) |
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exp `(("g" ,gdrv)))) |
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(out -> (derivation->output-path drv)) |
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(built? (built-derivations (list drv)))) |
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(return (and built? |
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(equal? guile |
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(readlink (string-append out "/guile-rocks")))))) |
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#:guile-for-build (package-derivation %store %bootstrap-guile))) |
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|
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(test-assert "mapm" |
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(every (lambda (monad run) |
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(with-monad monad |
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(equal? (run (mapm monad (lift1 1+ monad) (map return (iota 10)))) |
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(map 1+ (iota 10))))) |
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%monads |
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%monad-run)) |
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|
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(test-assert "sequence" |
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(every (lambda (monad run) |
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(let* ((input (iota 100)) |
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(order '())) |
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(define (frob i) |
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;; The side effect here is used to keep track of the order in |
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;; which monadic values are bound. |
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(set! order (cons i order)) |
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i) |
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|
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(and (equal? input |
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(run (sequence monad |
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(map (lift1 frob monad) input)))) |
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|
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;; Make sure this is from left to right. |
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(equal? order (reverse input))))) |
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%monads |
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%monad-run)) |
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|
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(test-assert "listm" |
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(every (lambda (monad run) |
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(run (with-monad monad |
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(let ((lst (listm monad |
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(return 1) (return 2) (return 3)))) |
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(mlet monad ((lst lst)) |
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(return (equal? '(1 2 3) lst))))))) |
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%monads |
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%monad-run)) |
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|
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(test-end "monads") |
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|
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|
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(exit (= (test-runner-fail-count (test-runner-current)) 0)) |
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