103 lines
3.7 KiB
Scheme
103 lines
3.7 KiB
Scheme
;;; GNU Guix --- Functional package management for GNU
|
|
;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
|
|
;;; Copyright © 2014 Eric Bavier <bavier@member.fsf.org>
|
|
;;; Copyright © 2020 Arun Isaac <arunisaac@systemreboot.net>
|
|
;;;
|
|
;;; 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 combinators)
|
|
#:use-module (ice-9 match)
|
|
#:use-module (ice-9 vlist)
|
|
#:export (fold2
|
|
fold-tree
|
|
fold-tree-leaves
|
|
compile-time-value))
|
|
|
|
;;; Commentary:
|
|
;;;
|
|
;;; This module provides useful combinators that complement SRFI-1 and
|
|
;;; friends.
|
|
;;;
|
|
;;; Code:
|
|
|
|
(define fold2
|
|
(case-lambda
|
|
((proc seed1 seed2 lst)
|
|
"Like `fold', but with a single list and two seeds."
|
|
(let loop ((result1 seed1)
|
|
(result2 seed2)
|
|
(lst lst))
|
|
(if (null? lst)
|
|
(values result1 result2)
|
|
(call-with-values
|
|
(lambda () (proc (car lst) result1 result2))
|
|
(lambda (result1 result2)
|
|
(loop result1 result2 (cdr lst)))))))
|
|
((proc seed1 seed2 lst1 lst2)
|
|
"Like `fold', but with two lists and two seeds."
|
|
(let loop ((result1 seed1)
|
|
(result2 seed2)
|
|
(lst1 lst1)
|
|
(lst2 lst2))
|
|
(if (or (null? lst1) (null? lst2))
|
|
(values result1 result2)
|
|
(call-with-values
|
|
(lambda () (proc (car lst1) (car lst2) result1 result2))
|
|
(lambda (result1 result2)
|
|
(loop result1 result2 (cdr lst1) (cdr lst2)))))))))
|
|
|
|
(define (fold-tree proc init children roots)
|
|
"Call (PROC NODE RESULT) for each node in the tree that is reachable from
|
|
ROOTS, using INIT as the initial value of RESULT. The order in which nodes
|
|
are traversed is not specified, however, each node is visited only once, based
|
|
on an eq? check. Children of a node to be visited are generated by
|
|
calling (CHILDREN NODE), the result of which should be a list of nodes that
|
|
are connected to NODE in the tree, or '() or #f if NODE is a leaf node."
|
|
(let loop ((result init)
|
|
(seen vlist-null)
|
|
(lst roots))
|
|
(match lst
|
|
(() result)
|
|
((head . tail)
|
|
(if (not (vhash-assq head seen))
|
|
(loop (proc head result)
|
|
(vhash-consq head #t seen)
|
|
(match (children head)
|
|
((or () #f) tail)
|
|
(children (append tail children))))
|
|
(loop result seen tail))))))
|
|
|
|
(define (fold-tree-leaves proc init children roots)
|
|
"Like fold-tree, but call (PROC NODE RESULT) only for leaf nodes."
|
|
(fold-tree
|
|
(lambda (node result)
|
|
(match (children node)
|
|
((or () #f) (proc node result))
|
|
(else result)))
|
|
init children roots))
|
|
|
|
(define-syntax compile-time-value ;not quite at home
|
|
(syntax-rules ()
|
|
"Evaluate the given expression at compile time. The expression must
|
|
evaluate to a simple datum."
|
|
((_ exp)
|
|
(let-syntax ((v (lambda (s)
|
|
(let ((val exp))
|
|
(syntax-case s ()
|
|
(_ #`'#,(datum->syntax s val)))))))
|
|
v))))
|
|
|
|
;;; combinators.scm ends here
|