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;;; Copyright © 2021 Gerald Sussman and Chris Hanson
;;; Copyright © 2021 David Thompson <dthompson2@worcester.edu>
;;;
;;; This program 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.
;;;
;;; This program 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 this program. If not, see
;;; <http://www.gnu.org/licenses/>.
(use-modules (ice-9 popen)
(srfi srfi-1))
;; 2.2.2 Implementation of the translator
(define-syntax-rule (assert cond)
(unless cond
(error "assertion failed" 'cond)))
;; I am excluding the write-bourne-shell-grep-command and
;; bourne-shell-command-string procedures in the book in favor of
;; using Guile's pipe API. open-pipe* does not open a shell but runs
;; grep directly, eliminating the need to do shell quoting. The book
;; asks "Are we having fun yet?" to which I say "yes, but I draw the
;; line at shell quoting."
(define (grep regexp string)
(let ((pipe (open-pipe* OPEN_WRITE "grep" "-e" regexp)))
(display string pipe)
(newline pipe)
(zero? (status:exit-val (close-pipe pipe)))))
(define (grep-test regexp . specs)
(for-each (lambda (spec)
(assert
(if (and (pair? spec) (eq? (car spec) 'not))
(not (grep regexp (list-ref spec 1)))
(grep regexp spec))))
specs))
(define (r:dot) ".")
(define (r:bol) "^")
(define (r:eol) "$")
(define (r:seq . exprs)
(string-append "\\(" (apply string-append exprs) "\\)"))
(define chars-needing-quoting
'(#\. #\[ #\\ #\^ #\$ #\*))
(define (r:quote string)
(r:seq
(list->string
(append-map (lambda (char)
(if (memv char chars-needing-quoting)
(list #\\ char)
(list char)))
(string->list string)))))
(grep-test (r:seq (r:quote "a") (r:dot) (r:quote "c"))
"abc")
(define (r:alt . exprs)
(if (pair? exprs)
(apply r:seq
(cons (car exprs)
(append-map (lambda (expr)
(list "\\|" expr))
(cdr exprs))))
(r:seq)))
(grep-test (r:alt (r:quote "foo") (r:quote "bar") (r:quote "baz"))
"foo" "bar" "baz" '(not "frob"))
(define (r:repeat min max expr)
(apply r:seq
(append (make-list min expr)
(cond
((not max)
(list expr "*"))
((= max min)
'())
(else
(make-list (- max min) (r:alt expr "")))))))
(grep-test (r:repeat 3 5 (r:alt (r:quote "cat") (r:quote "dog")))
"catdogcat"
"catcatdogdog"
"dogdogcatdogdog"
'(not "catdogfrog"))
(define (bracket string procedure)
(list->string
(append '(#\[)
(procedure (string->list string))
'(#\]))))
(define chars-needing-quoting-in-brackets
'(#\] #\^ #\-))
(define (quote-bracketed-contents members)
(define (optional char)
(if (memv char members)
(list char)
'()))
(append (optional #\])
(remove (lambda (c)
(memv c chars-needing-quoting-in-brackets))
members)
(optional #\^)
(optional #\-)))
(define (r:char-from string)
(case (string-length string)
((0) (r:seq))
((1) (r:quote string))
(else
(bracket string
(lambda (members)
(if (lset= eq? '(#\- #\^) members)
'(#\- #\^)
(quote-bracketed-contents members)))))))
(define (r:char-not-from string)
(bracket string
(lambda (members)
(cons #\^ (quote-bracketed-contents members)))))
;; Exercise 2.6: Adding * and + to regular expressions
(define (r:* expr)
(r:repeat 0 #f expr))
(define (r:+ expr)
(r:repeat 1 #f expr))
(grep-test (r:* (r:quote "foo"))
"" "foo" "bar")
(grep-test (r:seq (r:quote "foo") (r:* (r:quote "bar")))
"foo" "foobar" '(not ""))
(grep-test (r:+ (r:quote "foo"))
'(not "") "foo" "foofoo")
(grep-test (r:seq (r:quote "foo") (r:+ (r:quote "bar")))
'(not "foo") "foobar" "foobarbar")
;; Exercise 2.7: A bug, one bad joke, two tweaks, and a revelation
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