1 ;;;; -*- Mode: Lisp; Syntax: ANSI-Common-Lisp; Base: 10 -*-
2 ;;;; *************************************************************************
3 ;;;; FILE IDENTIFICATION
6 ;;;; Purpose: Pipes based on ideas from Norvig's PAIP book
7 ;;;; Programmers: Kevin M. Rosenberg and Peter Norvig
8 ;;;; Date Started: Apr 2000
10 ;;;; $Id: src.lisp,v 1.1 2003/03/15 00:48:56 kevin Exp $
12 ;;;; This file is Copyright (c) 2000-2002 by Kevin M. Rosenberg and
13 ;;;; Copyright (c) 1998-2002 by Peter Norvig.
14 ;;;; *************************************************************************
19 (defconstant +empty-pipe+ nil)
21 (defmacro make-pipe (head tail)
22 "Create a pipe by evaluating head and delaying tail."
23 `(cons ,head #'(lambda () ,tail)))
25 (defun pipe-tail (pipe)
26 "Return tail of pipe or list, and destructively update
27 the tail if it is a function."
28 (if (functionp (rest pipe))
29 (setf (rest pipe) (funcall (rest pipe)))
32 (defun pipe-head (pipe) (first pipe))
34 (defun pipe-elt (pipe i)
35 "The i-th element of pipe, 0-based."
38 (pipe-elt (pipe-tail pipe) (- i 1))))
41 (defun pipe-enumerate (pipe &key count key (result pipe))
42 "Go through all (or count) elements of pipe,
43 possibly applying the KEY function. (Try PRINT.)"
44 ;; Returns RESULT, which defaults to the pipe itself.
45 (if (or (eq pipe +empty-pipe+) (eql count 0))
48 (unless (null key) (funcall key (pipe-head pipe)))
49 (pipe-enumerate (pipe-tail pipe)
50 :count (if count (1- count))
51 :key key :result result))))
53 (defun pipe-values (pipe &optional count)
54 "Simple wrapper to return values of a pipe"
55 (pipe-enumerate pipe :count count))
57 (defun pipe-force (pipe)
58 "Force the enumeration of all of the pipe. Never returns
59 if the pipe is infinite in length."
60 (pipe-enumerate pipe))
62 (defun pipe-filter (predicate pipe)
63 "Keep only items in pipe satisfying predicate."
64 (if (eq pipe +empty-pipe+)
66 (let ((head (pipe-head pipe))
67 (tail (pipe-tail pipe)))
68 (if (funcall predicate head)
69 (make-pipe head (pipe-filter predicate tail))
70 (pipe-filter predicate tail)))))
73 (defun pipe-map (fn pipe)
74 "Map fn over pipe, delaying all but the first fn call."
75 (if (eq pipe +empty-pipe+)
77 (make-pipe (funcall fn (pipe-head pipe))
78 (pipe-map fn (pipe-tail pipe)))))
81 (defun pipe-map-filtering (fn pipe &optional filter-pred)
82 "Map fn over pipe, delaying all but the first fn call,
83 while filtering results."
84 (if (eq pipe +empty-pipe+)
86 (let* ((head (pipe-head pipe))
87 (tail (pipe-tail pipe))
88 (result (funcall fn head)))
89 (if (or (and filter-pred (funcall filter-pred result))
91 (make-pipe result (pipe-map-filtering fn tail filter-pred))
92 (pipe-map-filtering fn tail filter-pred)))))
95 (defun pipe-append (x y)
96 "Return a pipe that appends the elements of x and y."
97 (if (eq x +empty-pipe+)
99 (make-pipe (pipe-head x)
100 (pipe-append (pipe-tail x) y))))
103 (defun pipe-mappend (fn pipe)
104 "Lazily map fn over pipe, appending results."
105 (if (eq pipe +empty-pipe+)
107 (let ((x (funcall fn (pipe-head pipe))))
108 (make-pipe (pipe-head x)
109 (pipe-append (pipe-tail x)
110 (pipe-mappend fn (pipe-tail pipe)))))))
112 (defun pipe-mappend-filtering (fn pipe &optional filter-pred)
113 "Map fn over pipe, delaying all but the first fn call,
114 appending results while filtering."
115 (if (eq pipe +empty-pipe+)
117 (let* ((head (pipe-head pipe))
118 (tail (pipe-tail pipe))
119 (result (funcall fn head)))
120 (if (or (and filter-pred (funcall filter-pred result))
122 (make-pipe (pipe-head result)
123 (pipe-append (pipe-tail result)
124 (pipe-mappend-filtering fn tail filter-pred)))
125 (pipe-mappend-filtering fn tail filter-pred)))))