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; The SEQ Macro Language, Examples
; Copyright (C) 2008-2010 Centaur Technology
;
; Contact:
; Centaur Technology Formal Verification Group
; 7600-C N. Capital of Texas Highway, Suite 300, Austin, TX 78731, USA.
; http://www.centtech.com/
;
; License: (An MIT/X11-style license)
;
; Permission is hereby granted, free of charge, to any person obtaining a
; copy of this software and associated documentation files (the "Software"),
; to deal in the Software without restriction, including without limitation
; the rights to use, copy, modify, merge, publish, distribute, sublicense,
; and/or sell copies of the Software, and to permit persons to whom the
; Software is furnished to do so, subject to the following conditions:
;
; The above copyright notice and this permission notice shall be included in
; all copies or substantial portions of the Software.
;
; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
; DEALINGS IN THE SOFTWARE.
;
; Original author: Jared Davis <jared@centtech.com>
(in-package "ACL2")
(include-book "seq")
(set-verify-guards-eagerness 2)
; We will demonstrate how SEQ may be used to develop "parsers" that recognize
; certain kinds of lists. We begin with some straightforward utility
; functions.
(defun match-int (lst)
(cond ((not (consp lst))
(mv "Error: expecting int but found end of list." nil lst))
((not (integerp (car lst)))
(mv "Error: integer expected." nil lst))
(t
(mv nil (car lst) (cdr lst)))))
(defun match-string (lst)
(cond ((not (consp lst))
(mv "Error: expecting string but found end of list." nil lst))
((not (stringp (car lst)))
(mv "Error: string expected." nil lst))
(t
(mv nil (car lst) (cdr lst)))))
(defun match-three-ints (lst)
(seq lst
(a := (match-int lst))
(b := (match-int lst))
(c := (match-int lst))
(return (list (cons 'a a)
(cons 'b b)
(cons 'c c)))))
(match-three-ints '(1 2 3)) ;; Works, val is (a . 1) (b . 2) (c . 3)
(match-three-ints '(1 "2" 3)) ;; Fails, 2 is not an integer.
; This requires that the list beings with an integer, and furthermore if a
; string follows the integer, then there must be three strings after the
; integer. Notice how we can refer to the variables b, c, and d even if the
; "when" branch is not followed -- implicitly, all the variables in a SEQ
; program are bound to nil to begin with.
(defun match-int-then-maybe-three-strings (lst)
(seq lst
(a := (match-int lst))
(when (and (consp lst)
(stringp (car lst)))
(b := (match-string lst))
(c := (match-string lst))
(d := (match-string lst)))
(return (list (list :a a)
(list :b b)
(list :c c)
(list :d d)))))
; Fail, not even an int:
(match-int-then-maybe-three-strings nil)
; Fail, not even an int.
(match-int-then-maybe-three-strings '("1"))
; Works, one int is okay.
(match-int-then-maybe-three-strings '(1))
; Works, one int is okay, leaves 2 in lst.
(match-int-then-maybe-three-strings '(1 2))
; Fail, if a string is there, we need three strings.
(match-int-then-maybe-three-strings '(1 "foo"))
; Works, an int and 3 strings.
(match-int-then-maybe-three-strings '(1 "foo" "bar" "baz"))
; Works, an int and 3 strings; leaves 2 3 4 in the lst
(match-int-then-maybe-three-strings '(1 "foo" "bar" "baz" 2 3 4))
; SEQ does not have any looping construct, but you can recursively call the
; current function as an action. So this matches a non-empty list of
; integers.
(defun match-int-list (lst)
(seq lst
(first := (match-int lst))
(when (consp lst)
(rest := (match-int-list lst)))
(return (cons first rest))))
(match-int-list nil) ;; fail, need at least one int
(match-int-list '(1 2 3 4)) ;; works
(match-int-list '(1 2 3 4 "five")) ;; fail, not all integers
; Here's another way to match a non-empty list of integers, which also uses
; an "early return" in the unless block.
(defun match-int-list2 (lst)
(seq lst
(first := (match-int lst))
(unless (consp lst)
(return (list first)))
(rest := (match-int-list2 lst))
(return (cons first rest))))
(match-int-list2 nil) ;; fail, need at least one int
(match-int-list2 '(1 2 3 4)) ;; works
(match-int-list2 '(1 2 3 4 "five")) ;; fail, not all integers
; And here's a variant that permits an empty list. Early returns are nice
; for avoiding nested whens, etc.
(defun match-ints (lst)
(seq lst
(when (atom lst)
(return nil))
(first := (match-int lst))
(rest := (match-ints lst))
(return (cons first rest))))
(match-ints nil) ;; works
(match-ints '(1 2 3)) ;; works
(match-ints '(1 2 3 "four")) ;; fail, not all integers
; And here's a tail-recursive variant that accumulates the integers into acc
; in reverse, then reverses them at the end.
(defun tr-match-ints (lst acc)
(declare (xargs :guard (true-listp acc)))
(seq lst
(when (atom lst)
(return (reverse acc)))
(a := (match-int lst))
(return-raw (tr-match-ints lst (cons a acc)))))
(tr-match-ints nil nil) ;; works
(tr-match-ints '(1 2 3) nil) ;; works
(tr-match-ints '(1 2 3 "four") nil) ;; fail, not all integers
#||
; stack overflows on my Lisp
; segfaults on gcl, watch out.
(comp 'match-ints)
(mv-let (erp val lst)
(match-ints (make-list 10000000 :initial-element 0))
(declare (ignore val lst))
erp)
||#
; does not stack overflow on my Lisp
(comp 'tr-match-ints)
(mv-let (erp val lst)
(tr-match-ints (make-list 10000000 :initial-element 0) nil)
(declare (ignore val lst))
erp)
; And here's a function that reads as many ints as it can.
(defun match-front-ints (lst)
(seq lst
(unless (and (consp lst)
(integerp (car lst)))
(return nil))
(a := (match-int lst))
(b := (match-front-ints lst))
(return (cons a b))))
(match-front-ints nil) ;; fine, no ints
(match-front-ints '("foo" 1 2 3)) ;; fine, but no front ints
(match-front-ints '(1 2 3 "foo" 4 5)) ;; fine, but only matches 1 2 3
; Now let's try backtracking. We'll write a function that either reads "int
; int string", or "string string int", or fails.
(defun match-iis-or-ssi (lst)
(seq-backtrack lst
;; Option 1: Read int, int, string.
((i1 := (match-int lst))
(i2 := (match-int lst))
(str := (match-string lst))
(return (list :OPTION-1 i1 i2 str)))
;; Option 2: Read string, string, int.
((s1 := (match-string lst))
(s2 := (match-string lst))
(int := (match-int lst))
(return (list :OPTION-2 s1 s2 int)))))
(match-iis-or-ssi '(1 1 "foo" 2 3 4)) ;; works, option 1
(match-iis-or-ssi '("foo" "bar" 1 9)) ;; works, option 2
(match-iis-or-ssi '(1 "foo" 2 2 4)) ;; fails
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