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578 lines
21 KiB
Scheme
578 lines
21 KiB
Scheme
;;; -*- mode: scheme; coding: utf-8; -*-
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;;;
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;;; Copyright (C) 2009, 2010, 2011, 2012 Free Software Foundation, Inc.
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;;;
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;;; This library is free software; you can redistribute it and/or
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;;; modify it under the terms of the GNU Lesser General Public
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;;; License as published by the Free Software Foundation; either
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;;; version 3 of the License, or (at your option) any later version.
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;;;
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;;; This library is distributed in the hope that it will be useful,
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;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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;;; Lesser General Public License for more details.
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;;;
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;;; You should have received a copy of the GNU Lesser General Public
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;;; License along with this library; if not, write to the Free Software
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;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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(define-module (ice-9 vlist)
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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-9 gnu)
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#:use-module (srfi srfi-26)
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#:use-module (ice-9 format)
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#:export (vlist? vlist-cons vlist-head vlist-tail vlist-null?
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vlist-null list->vlist vlist-ref vlist-drop vlist-take
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vlist-length vlist-fold vlist-fold-right vlist-map
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vlist-unfold vlist-unfold-right vlist-append
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vlist-reverse vlist-filter vlist-delete vlist->list
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vlist-for-each
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block-growth-factor
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vhash? vhash-cons vhash-consq vhash-consv
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vhash-assoc vhash-assq vhash-assv
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vhash-delete vhash-delq vhash-delv
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vhash-fold vhash-fold-right
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vhash-fold* vhash-foldq* vhash-foldv*
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alist->vhash))
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;;; Author: Ludovic Courtès <ludo@gnu.org>
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;;;
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;;; Commentary:
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;;;
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;;; This module provides an implementations of vlists, a functional list-like
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;;; data structure described by Phil Bagwell in "Fast Functional Lists,
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;;; Hash-Lists, Dequeues and Variable-Length Arrays", EPFL Technical Report,
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;;; 2002.
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;;;
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;;; The idea is to store vlist elements in increasingly large contiguous blocks
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;;; (implemented as vectors here). These blocks are linked to one another using
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;;; a pointer to the next block (called `block-base' here) and an offset within
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;;; that block (`block-offset' here). The size of these blocks form a geometric
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;;; series with ratio `block-growth-factor'.
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;;;
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;;; In the best case (e.g., using a vlist returned by `list->vlist'),
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;;; elements from the first half of an N-element vlist are accessed in O(1)
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;;; (assuming `block-growth-factor' is 2), and `vlist-length' takes only
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;;; O(ln(N)). Furthermore, the data structure improves data locality since
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;;; vlist elements are adjacent, which plays well with caches.
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;;;
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;;; Code:
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;;;
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;;; VList Blocks and Block Descriptors.
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;;;
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(define block-growth-factor
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(make-fluid 2))
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(define-syntax-rule (define-inline (name formals ...) body ...)
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;; Work around the lack of an inliner.
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(define-syntax name
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(syntax-rules ()
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((_ formals ...)
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(begin body ...)))))
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(define-inline (make-block base offset size hash-tab?)
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;; Return a block (and block descriptor) of SIZE elements pointing to BASE
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;; at OFFSET. If HASH-TAB? is true, a "hash table" is also added.
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;; Note: We use `next-free' instead of `last-used' as suggested by Bagwell.
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;; XXX: We could improve locality here by having a single vector but currently
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;; the extra arithmetic outweighs the benefits (!).
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(vector (make-vector size)
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base offset size 0
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(and hash-tab? (make-vector size #f))))
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(define-syntax-rule (define-block-accessor name index)
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(define-inline (name block)
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(vector-ref block index)))
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(define-block-accessor block-content 0)
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(define-block-accessor block-base 1)
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(define-block-accessor block-offset 2)
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(define-block-accessor block-size 3)
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(define-block-accessor block-next-free 4)
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(define-block-accessor block-hash-table 5)
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(define-inline (increment-block-next-free! block)
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(vector-set! block 4
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(+ (block-next-free block) 1)))
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(define-inline (block-append! block value)
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;; This is not thread-safe. To fix it, see Section 2.8 of the paper.
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(let ((offset (block-next-free block)))
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(increment-block-next-free! block)
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(vector-set! (block-content block) offset value)
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#t))
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(define-inline (block-ref block offset)
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(vector-ref (block-content block) offset))
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(define-inline (block-ref* block offset)
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(let ((v (block-ref block offset)))
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(if (block-hash-table block)
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(car v) ;; hide the vhash link
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v)))
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(define-inline (block-hash-table-ref block offset)
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(vector-ref (block-hash-table block) offset))
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(define-inline (block-hash-table-set! block offset value)
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(vector-set! (block-hash-table block) offset value))
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(define block-null
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;; The null block.
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(make-block #f 0 0 #f))
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;;;
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;;; VLists.
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;;;
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(define-record-type <vlist>
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;; A vlist is just a base+offset pair pointing to a block.
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;; XXX: Allocating a <vlist> record in addition to the block at each
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;; `vlist-cons' call is inefficient. However, Bagwell's hack to avoid it
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;; (Section 2.2) would require GC_ALL_INTERIOR_POINTERS, which would be a
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;; performance hit for everyone.
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(make-vlist base offset)
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vlist?
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(base vlist-base)
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(offset vlist-offset))
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(set-record-type-printer! <vlist>
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(lambda (vl port)
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(cond ((vlist-null? vl)
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(format port "#<vlist ()>"))
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((block-hash-table (vlist-base vl))
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(format port "#<vhash ~x ~a pairs>"
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(object-address vl)
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(vhash-fold (lambda (k v r)
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(+ 1 r))
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0
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vl)))
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(else
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(format port "#<vlist ~a>"
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(vlist->list vl))))))
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(define vlist-null
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;; The empty vlist.
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(make-vlist block-null 0))
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(define-inline (block-cons item vlist hash-tab?)
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(let loop ((base (vlist-base vlist))
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(offset (+ 1 (vlist-offset vlist))))
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(if (and (< offset (block-size base))
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(= offset (block-next-free base))
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(block-append! base item))
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(make-vlist base offset)
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(let ((size (cond ((eq? base block-null) 1)
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((< offset (block-size base))
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;; new vlist head
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1)
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(else
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(* (fluid-ref block-growth-factor)
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(block-size base))))))
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;; Prepend a new block pointing to BASE.
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(loop (make-block base (- offset 1) size hash-tab?)
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0)))))
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(define (vlist-cons item vlist)
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"Return a new vlist with @var{item} as its head and @var{vlist} as its
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tail."
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;; Note: Calling `vlist-cons' on a vhash will not do the right thing: it
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;; doesn't box ITEM so that it can have the hidden "next" link used by
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;; vhash items, and it passes `#f' as the HASH-TAB? argument to
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;; `block-cons'. However, inserting all the checks here has an important
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;; performance penalty, hence this choice.
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(block-cons item vlist #f))
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(define (vlist-head vlist)
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"Return the head of @var{vlist}."
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(let ((base (vlist-base vlist))
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(offset (vlist-offset vlist)))
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(block-ref* base offset)))
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(define (vlist-tail vlist)
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"Return the tail of @var{vlist}."
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(let ((base (vlist-base vlist))
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(offset (vlist-offset vlist)))
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(if (> offset 0)
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(make-vlist base (- offset 1))
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(make-vlist (block-base base)
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(block-offset base)))))
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(define (vlist-null? vlist)
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"Return true if @var{vlist} is empty."
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(let ((base (vlist-base vlist)))
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(and (not (block-base base))
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(= 0 (block-size base)))))
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;;;
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;;; VList Utilities.
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;;;
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(define (list->vlist lst)
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"Return a new vlist whose contents correspond to @var{lst}."
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(vlist-reverse (fold vlist-cons vlist-null lst)))
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(define (vlist-fold proc init vlist)
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"Fold over @var{vlist}, calling @var{proc} for each element."
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;; FIXME: Handle multiple lists.
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(let loop ((base (vlist-base vlist))
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(offset (vlist-offset vlist))
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(result init))
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(if (eq? base block-null)
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result
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(let* ((next (- offset 1))
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(done? (< next 0)))
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(loop (if done? (block-base base) base)
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(if done? (block-offset base) next)
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(proc (block-ref* base offset) result))))))
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(define (vlist-fold-right proc init vlist)
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"Fold over @var{vlist}, calling @var{proc} for each element, starting from
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the last element."
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(define len (vlist-length vlist))
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(let loop ((index (1- len))
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(result init))
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(if (< index 0)
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result
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(loop (1- index)
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(proc (vlist-ref vlist index) result)))))
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(define (vlist-reverse vlist)
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"Return a new @var{vlist} whose content are those of @var{vlist} in reverse
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order."
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(vlist-fold vlist-cons vlist-null vlist))
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(define (vlist-map proc vlist)
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"Map @var{proc} over the elements of @var{vlist} and return a new vlist."
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(vlist-fold (lambda (item result)
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(vlist-cons (proc item) result))
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vlist-null
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(vlist-reverse vlist)))
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(define (vlist->list vlist)
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"Return a new list whose contents match those of @var{vlist}."
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(vlist-fold-right cons '() vlist))
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(define (vlist-ref vlist index)
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"Return the element at index @var{index} in @var{vlist}."
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(let loop ((index index)
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(base (vlist-base vlist))
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(offset (vlist-offset vlist)))
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(if (<= index offset)
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(block-ref* base (- offset index))
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(loop (- index offset 1)
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(block-base base)
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(block-offset base)))))
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(define (vlist-drop vlist count)
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"Return a new vlist that does not contain the @var{count} first elements of
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@var{vlist}."
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(let loop ((count count)
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(base (vlist-base vlist))
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(offset (vlist-offset vlist)))
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(if (<= count offset)
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(make-vlist base (- offset count))
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(loop (- count offset 1)
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(block-base base)
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(block-offset base)))))
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(define (vlist-take vlist count)
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"Return a new vlist that contains only the @var{count} first elements of
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@var{vlist}."
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(let loop ((count count)
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(vlist vlist)
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(result vlist-null))
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(if (= 0 count)
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(vlist-reverse result)
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(loop (- count 1)
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(vlist-tail vlist)
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(vlist-cons (vlist-head vlist) result)))))
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(define (vlist-filter pred vlist)
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"Return a new vlist containing all the elements from @var{vlist} that
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satisfy @var{pred}."
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(vlist-fold-right (lambda (e v)
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(if (pred e)
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(vlist-cons e v)
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v))
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vlist-null
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vlist))
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(define* (vlist-delete x vlist #:optional (equal? equal?))
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"Return a new vlist corresponding to @var{vlist} without the elements
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@var{equal?} to @var{x}."
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(vlist-filter (lambda (e)
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(not (equal? e x)))
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vlist))
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(define (vlist-length vlist)
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"Return the length of @var{vlist}."
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(let loop ((base (vlist-base vlist))
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(len (vlist-offset vlist)))
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(if (eq? base block-null)
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len
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(loop (block-base base)
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(+ len 1 (block-offset base))))))
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(define* (vlist-unfold p f g seed
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#:optional (tail-gen (lambda (x) vlist-null)))
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"Return a new vlist. See the description of SRFI-1 `unfold' for details."
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(let uf ((seed seed))
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(if (p seed)
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(tail-gen seed)
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(vlist-cons (f seed)
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(uf (g seed))))))
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(define* (vlist-unfold-right p f g seed #:optional (tail vlist-null))
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"Return a new vlist. See the description of SRFI-1 `unfold-right' for
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details."
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(let uf ((seed seed) (lis tail))
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(if (p seed)
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lis
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(uf (g seed) (vlist-cons (f seed) lis)))))
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(define (vlist-append . vlists)
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"Append the given lists."
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(if (null? vlists)
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vlist-null
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(fold-right (lambda (vlist result)
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(vlist-fold-right (lambda (e v)
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(vlist-cons e v))
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result
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vlist))
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vlist-null
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vlists)))
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(define (vlist-for-each proc vlist)
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"Call @var{proc} on each element of @var{vlist}. The result is unspecified."
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(vlist-fold (lambda (item x)
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(proc item))
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(if #f #f)
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vlist))
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;;;
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;;; Hash Lists, aka. `VHash'.
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;;;
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;; Assume keys K1 and K2, H = hash(K1) = hash(K2), and two values V1 and V2
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;; associated with K1 and K2, respectively. The resulting layout is a
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;; follows:
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;;
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;; ,--------------------.
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;; | ,-> (K1 . V1) ---. |
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;; | | | |
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;; | | (K2 . V2) <--' |
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;; | | |
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;; +-|------------------+
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;; | | |
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;; | | |
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;; | `-- O <---------------H
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;; | |
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;; `--------------------'
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;;
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;; The bottom part is the "hash table" part of the vhash, as returned by
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;; `block-hash-table'; the other half is the data part. O is the offset of
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;; the first value associated with a key that hashes to H in the data part.
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;; The (K1 . V1) pair has a "hidden" link to the (K2 . V2) pair; hiding the
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;; link is handled by `block-ref'.
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;; This API potentially requires users to repeat which hash function and which
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;; equality predicate to use. This can lead to unpredictable results if they
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;; are used in consistenly, e.g., between `vhash-cons' and `vhash-assoc', which
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;; is undesirable, as argued in http://savannah.gnu.org/bugs/?22159 . OTOH, two
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;; arguments can be made in favor of this API:
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;;
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;; - It's consistent with how alists are handled in SRFI-1.
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;;
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;; - In practice, users will probably consistenly use either the `q', the `v',
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;; or the plain variant (`vlist-cons' and `vlist-assoc' without any optional
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;; argument), i.e., they will rarely explicitly pass a hash function or
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;; equality predicate.
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(define (vhash? obj)
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"Return true if @var{obj} is a hash list."
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(and (vlist? obj)
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(let ((base (vlist-base obj)))
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(and base
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(vector? (block-hash-table base))))))
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(define* (vhash-cons key value vhash #:optional (hash hash))
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"Return a new hash list based on @var{vhash} where @var{key} is associated
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with @var{value}. Use @var{hash} to compute @var{key}'s hash."
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(let* ((key+value (cons key value))
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(entry (cons key+value #f))
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(vlist (block-cons entry vhash #t))
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(base (vlist-base vlist))
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(khash (hash key (block-size base))))
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(let ((o (block-hash-table-ref base khash)))
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(if o (set-cdr! entry o)))
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(block-hash-table-set! base khash
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(vlist-offset vlist))
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vlist))
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(define vhash-consq (cut vhash-cons <> <> <> hashq))
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(define vhash-consv (cut vhash-cons <> <> <> hashv))
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(define-inline (%vhash-fold* proc init key vhash equal? hash)
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;; Fold over all the values associated with KEY in VHASH.
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(define khash
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(let ((size (block-size (vlist-base vhash))))
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(and (> size 0) (hash key size))))
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(let loop ((base (vlist-base vhash))
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(khash khash)
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(offset (and khash
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(block-hash-table-ref (vlist-base vhash)
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khash)))
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(max-offset (vlist-offset vhash))
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(result init))
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(let ((answer (and offset (block-ref base offset))))
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(cond ((and (pair? answer)
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(<= offset max-offset)
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(let ((answer-key (caar answer)))
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(equal? key answer-key)))
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(let ((result (proc (cdar answer) result))
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(next-offset (cdr answer)))
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(loop base khash next-offset max-offset result)))
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((and (pair? answer) (cdr answer))
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=>
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(lambda (next-offset)
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(loop base khash next-offset max-offset result)))
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(else
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(let ((next-base (block-base base)))
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(if (and next-base (> (block-size next-base) 0))
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(let* ((khash (hash key (block-size next-base)))
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(offset (block-hash-table-ref next-base khash)))
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(loop next-base khash offset (block-offset base)
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result))
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result)))))))
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(define* (vhash-fold* proc init key vhash
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#:optional (equal? equal?) (hash hash))
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"Fold over all the values associated with @var{key} in @var{vhash}, with each
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call to @var{proc} having the form @code{(proc value result)}, where
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@var{result} is the result of the previous call to @var{proc} and @var{init} the
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value of @var{result} for the first call to @var{proc}."
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(%vhash-fold* proc init key vhash equal? hash))
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(define (vhash-foldq* proc init key vhash)
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"Same as @code{vhash-fold*}, but using @code{hashq} and @code{eq?}."
|
||
(%vhash-fold* proc init key vhash eq? hashq))
|
||
|
||
(define (vhash-foldv* proc init key vhash)
|
||
"Same as @code{vhash-fold*}, but using @code{hashv} and @code{eqv?}."
|
||
(%vhash-fold* proc init key vhash eqv? hashv))
|
||
|
||
(define-inline (%vhash-assoc key vhash equal? hash)
|
||
;; A specialization of `vhash-fold*' that stops when the first value
|
||
;; associated with KEY is found or when the end-of-list is reached. Inline to
|
||
;; make sure `vhash-assq' gets to use the `eq?' instruction instead of calling
|
||
;; the `eq?' subr.
|
||
(define khash
|
||
(let ((size (block-size (vlist-base vhash))))
|
||
(and (> size 0) (hash key size))))
|
||
|
||
(let loop ((base (vlist-base vhash))
|
||
(khash khash)
|
||
(offset (and khash
|
||
(block-hash-table-ref (vlist-base vhash)
|
||
khash)))
|
||
(max-offset (vlist-offset vhash)))
|
||
(let ((answer (and offset (block-ref base offset))))
|
||
(cond ((and (pair? answer)
|
||
(<= offset max-offset)
|
||
(let ((answer-key (caar answer)))
|
||
(equal? key answer-key)))
|
||
(car answer))
|
||
((and (pair? answer) (cdr answer))
|
||
=>
|
||
(lambda (next-offset)
|
||
(loop base khash next-offset max-offset)))
|
||
(else
|
||
(let ((next-base (block-base base)))
|
||
(and next-base
|
||
(> (block-size next-base) 0)
|
||
(let* ((khash (hash key (block-size next-base)))
|
||
(offset (block-hash-table-ref next-base khash)))
|
||
(loop next-base khash offset
|
||
(block-offset base))))))))))
|
||
|
||
(define* (vhash-assoc key vhash #:optional (equal? equal?) (hash hash))
|
||
"Return the first key/value pair from @var{vhash} whose key is equal to
|
||
@var{key} according to the @var{equal?} equality predicate."
|
||
(%vhash-assoc key vhash equal? hash))
|
||
|
||
(define (vhash-assq key vhash)
|
||
"Return the first key/value pair from @var{vhash} whose key is @code{eq?} to
|
||
@var{key}."
|
||
(%vhash-assoc key vhash eq? hashq))
|
||
|
||
(define (vhash-assv key vhash)
|
||
"Return the first key/value pair from @var{vhash} whose key is @code{eqv?} to
|
||
@var{key}."
|
||
(%vhash-assoc key vhash eqv? hashv))
|
||
|
||
(define* (vhash-delete key vhash #:optional (equal? equal?) (hash hash))
|
||
"Remove all associations from @var{vhash} with @var{key}, comparing keys
|
||
with @var{equal?}."
|
||
(if (vhash-assoc key vhash equal? hash)
|
||
(vlist-fold (lambda (k+v result)
|
||
(let ((k (car k+v))
|
||
(v (cdr k+v)))
|
||
(if (equal? k key)
|
||
result
|
||
(vhash-cons k v result hash))))
|
||
vlist-null
|
||
vhash)
|
||
vhash))
|
||
|
||
(define vhash-delq (cut vhash-delete <> <> eq? hashq))
|
||
(define vhash-delv (cut vhash-delete <> <> eqv? hashv))
|
||
|
||
(define (vhash-fold proc init vhash)
|
||
"Fold over the key/pair elements of @var{vhash} from left to right, with
|
||
each call to @var{proc} having the form @code{(@var{proc} key value result)},
|
||
where @var{result} is the result of the previous call to @var{proc} and
|
||
@var{init} the value of @var{result} for the first call to @var{proc}."
|
||
(vlist-fold (lambda (key+value result)
|
||
(proc (car key+value) (cdr key+value)
|
||
result))
|
||
init
|
||
vhash))
|
||
|
||
(define (vhash-fold-right proc init vhash)
|
||
"Fold over the key/pair elements of @var{vhash} from right to left, with
|
||
each call to @var{proc} having the form @code{(@var{proc} key value result)},
|
||
where @var{result} is the result of the previous call to @var{proc} and
|
||
@var{init} the value of @var{result} for the first call to @var{proc}."
|
||
(vlist-fold-right (lambda (key+value result)
|
||
(proc (car key+value) (cdr key+value)
|
||
result))
|
||
init
|
||
vhash))
|
||
|
||
(define* (alist->vhash alist #:optional (hash hash))
|
||
"Return the vhash corresponding to @var{alist}, an association list."
|
||
(fold-right (lambda (pair result)
|
||
(vhash-cons (car pair) (cdr pair) result hash))
|
||
vlist-null
|
||
alist))
|
||
|
||
;;; vlist.scm ends here
|