I want to split a string on an arbitrary regular expression (similar to clojure.string/split) but keep the matches in the result. One way to do this is with lookaround in the regex but this doesn't work well in ClojureScript because it's not supported by all browsers.
In my case, the regex is #"\{\{\s*[A-Za-z0-9_\.]+?\s*\}\}")
So for example, foo {{bar}} baz should be split into ("foo " "{{bar}}" " baz").
Thanks!
One possible solution is to choose some special character as a delimiter, insert it into the string during replace and then split on that. Here I used exclamation mark:
Require: [clojure.string :as s]
(-> "foo {{bar}} baz"
(s/replace #"\{\{\s*[A-Za-z0-9_\.]+?\s*\}\}" "!$0!")
(s/split #"!"))
=> ["foo " "{{bar}}" " baz"]
The split in both clojure and java takes regular expression as parameter to split. But I just want to use normal char to split. The char passed in could be "|", ","," " etc. how to split a line by that char?
I need some function like (split string a-char). And this function will be called at very high frequency, so need good performance. Any good solution.
There are a few features in java.util.regex.Pattern class that support treating strings as literal regular expressions. This is useful for cases such as these. #cgrand already alluded to (Pattern/quote s) in a comment to another answer. One more such feature is the LITERAL flag (documented here). It can be used when compiling literal regular expression patterns. Remember that #"foo" in Clojure is essentially syntax sugar for (Pattern/compile "foo"). Putting it all together we have:
(import 'java.util.regex.Pattern)
(clojure.string/split "foo[]bar" (Pattern/compile "[]" Pattern/LITERAL))
;; ["foo" "bar"]
Just make your character a regex by properly escaping special characters and use the default regex split (which is fastest by far).
This version will make a regexp that automatically escapes every character or string within it
(defn char-to-regex
[c]
(re-pattern (java.util.regex.Pattern/quote (str c))))
This version will make a regexp that escapes a single character if it's within the special character range of regexps
(defn char-to-regex
[c]
(if ((set "<([{\\^-=$!|]})?*+.>") c)
(re-pattern (str "\\" c))
(re-pattern c)))
Make sure to bind the regex, so you don't call char-to-regex over and over again if you need to do multiple splits
(let [break (char-to-regex \|)]
(clojure.string/split "This is | the string | to | split" break))
=> ["This is " " the string " " to " " split"]
I am trying to tokenize a string using clojure. The basic tokenization rules require the string to be split into separate symbols as follows:
String literals of the form "hello world" are a single token
Every word that is not part of a string literal is a single token
Every non-word character is a separate token
For example, given the string:
length=Keyboard.readInt("HOW MANY NUMBERS? ");
I would like it to be tokenized as:
["length" "=" "Keyboard" "." "readInt" "(" "\"HOW MANY NUMBERS? \"" ")" ";"]
I have been able to write a function to split a string according to rules 2 and 3 above. I am having trouble fulfilling the first rule.
Meaning, currently the above string is split as follows:
["let" "length" "=" "Keyboard" "." "readInt" "(" "\"HOW" "MANY" "NUMBERS?" "\"" ")" ";"]
Here is my function:
(defn TokenizeJackLine [LineOfJackFile]
(filter not-empty
(->
(string/trim LineOfJackFile)
; get rid of all comments
(string/replace #"(//.*)|(\s*/?\*.*?($|\*/))|([^/\*]*\*/)" "")
; split into tokens using 0-width look-ahead
(string/split #"\s+|(?<=[\{\}\(\)\[\]\.,;+\-\*/&\|<>=~])|(?=[\{\}\(\)\[\]\.,;+\-\*/&\|<>=~])")
)))
How can I write a function that will split a string into tokens following all three of the above rules? Alternatively, what other approach should I take to achieve the desired tokenization? Thank you.
Removing the initial \s+| from your split makes it work the way that you want it to. That is causing the string to split on white space characters.
(defn TokenizeJackLine [LineOfJackFile]
(filter not-empty
(->
(clojure.string/trim LineOfJackFile)
; get rid of all comments
(clojure.string/replace #"(//.*)|(\s*/?\*.*?($|\*/))|([^/\*]*\*/)" "")
; split into tokens using 0-width look-ahead
(clojure.string/split #"(?<=[\{\}\(\)\[\]\.,;+\-\*/&\|<>=~])|(?=[\{\}\(\)\[\]\.,;+\-\*/&\|<>=~])")
)))
(def input "length=Keyboard.readInt(\"HOW MANY NUMBERS? \");")
(TokenizeJackLine input)
Produces this output:
("length" "=" "Keyboard" "." "readInt" "(" "\"HOW MANY NUMBERS? \"" ")" ";")
i think I found a bug in clojure, can anyone explain why the backslash is missing from the output?
(clojure.string/replace "The color? is red." #"[?.]" #(str "zzz\\j" %1 %1))
=> "The colorzzzj?? is redzzzj.."
This isn't a bug. The string returned by the function in the 3rd parameter is parsed for escape sequences so that you can do things like this:
(clojure.string/replace "The color? is red." #"([?.])" "\\$1$1")
; => "The color$1? is red$1."
Notice how the first $ is escaped by the backslash, whereas the second serves as the identifier for a capture group. Change your code to use four backslashes and it works:
(clojure.string/replace "The color? is red." #"[?.]" #(str "zzz\\\\j" %1 %1))
Please check the function documentation at: http://clojuredocs.org/clojure_core/clojure.string/replace
Specifically:
Note: When replace-first or replace have a regex pattern as their
match argument, dollar sign ($) and backslash (\) characters in the
replacement string are treated specially.
I admit significant bias toward liking PCRE regexps much better than emacs, if no no other reason that when I type a '(' I pretty much always want a grouping operator. And, of course, \w and similar are SO much more convenient than the other equivalents.
But it would be crazy to expect to change the internals of emacs, of course. But it should be possible to convert from a PCRE experssion to an emacs expression, I'd think, and do all the needed conversions so I can write:
(defun my-super-regexp-function ...
(search-forward (pcre-convert "__\\w: \d+")))
(or similar).
Anyone know of a elisp library that can do this?
Edit: Selecting a response from the answers below...
Wow, I love coming back from 4 days of vacation to find a slew of interesting answers to sort through! I love the work that went into the solutions of both types.
In the end, it looks like both the exec-a-script and straight elisp versions of the solutions would both work, but from a pure speed and "correctness" approach the elisp version is certainly the one that people would prefer (myself included).
https://github.com/joddie/pcre2el is the up-to-date version of this answer.
pcre2el or rxt (RegeXp Translator or RegeXp Tools) is a utility for working with regular expressions in Emacs, based on a recursive-descent parser for regexp syntax. In addition to converting (a subset of) PCRE syntax into its Emacs equivalent, it can do the following:
convert Emacs syntax to PCRE
convert either syntax to rx, an S-expression based regexp syntax
untangle complex regexps by showing the parse tree in rx form and highlighting the corresponding chunks of code
show the complete list of strings (productions) matching a regexp, provided the list is finite
provide live font-locking of regexp syntax (so far only for Elisp buffers – other modes on the TODO list)
The text of the original answer follows...
Here's a quick and ugly Emacs lisp solution (EDIT: now located more permanently here). It's based mostly on the description in the pcrepattern man page, and works token by token, converting only the following constructions:
parenthesis grouping ( .. )
alternation |
numerical repeats {M,N}
string quoting \Q .. \E
simple character escapes: \a, \c, \e, \f, \n, \r, \t, \x, and \ + octal digits
character classes: \d, \D, \h, \H, \s, \S, \v, \V
\w and \W left as they are (using Emacs' own idea of word and non-word characters)
It doesn't do anything with more complicated PCRE assertions, but it does try to convert escapes inside character classes. In the case of character classes including something like \D, this is done by converting into a non-capturing group with alternation.
It passes the tests I wrote for it, but there are certainly bugs, and the method of scanning token-by-token is probably slow. In other words, no warranty. But perhaps it will do enough of the simpler part of the job for some purposes. Interested parties are invited to improve it ;-)
(eval-when-compile (require 'cl))
(defvar pcre-horizontal-whitespace-chars
(mapconcat 'char-to-string
'(#x0009 #x0020 #x00A0 #x1680 #x180E #x2000 #x2001 #x2002 #x2003
#x2004 #x2005 #x2006 #x2007 #x2008 #x2009 #x200A #x202F
#x205F #x3000)
""))
(defvar pcre-vertical-whitespace-chars
(mapconcat 'char-to-string
'(#x000A #x000B #x000C #x000D #x0085 #x2028 #x2029) ""))
(defvar pcre-whitespace-chars
(mapconcat 'char-to-string '(9 10 12 13 32) ""))
(defvar pcre-horizontal-whitespace
(concat "[" pcre-horizontal-whitespace-chars "]"))
(defvar pcre-non-horizontal-whitespace
(concat "[^" pcre-horizontal-whitespace-chars "]"))
(defvar pcre-vertical-whitespace
(concat "[" pcre-vertical-whitespace-chars "]"))
(defvar pcre-non-vertical-whitespace
(concat "[^" pcre-vertical-whitespace-chars "]"))
(defvar pcre-whitespace (concat "[" pcre-whitespace-chars "]"))
(defvar pcre-non-whitespace (concat "[^" pcre-whitespace-chars "]"))
(eval-when-compile
(defmacro pcre-token-case (&rest cases)
"Consume a token at point and evaluate corresponding forms.
CASES is a list of `cond'-like clauses, (REGEXP FORMS
...). Considering CASES in order, if the text at point matches
REGEXP then moves point over the matched string and returns the
value of FORMS. Returns `nil' if none of the CASES matches."
(declare (debug (&rest (sexp &rest form))))
`(cond
,#(mapcar
(lambda (case)
(let ((token (car case))
(action (cdr case)))
`((looking-at ,token)
(goto-char (match-end 0))
,#action)))
cases)
(t nil))))
(defun pcre-to-elisp (pcre)
"Convert PCRE, a regexp in PCRE notation, into Elisp string form."
(with-temp-buffer
(insert pcre)
(goto-char (point-min))
(let ((capture-count 0) (accum '())
(case-fold-search nil))
(while (not (eobp))
(let ((translated
(or
;; Handle tokens that are treated the same in
;; character classes
(pcre-re-or-class-token-to-elisp)
;; Other tokens
(pcre-token-case
("|" "\\|")
("(" (incf capture-count) "\\(")
(")" "\\)")
("{" "\\{")
("}" "\\}")
;; Character class
("\\[" (pcre-char-class-to-elisp))
;; Backslash + digits => backreference or octal char?
("\\\\\\([0-9]+\\)"
(let* ((digits (match-string 1))
(dec (string-to-number digits)))
;; from "man pcrepattern": If the number is
;; less than 10, or if there have been at
;; least that many previous capturing left
;; parentheses in the expression, the entire
;; sequence is taken as a back reference.
(cond ((< dec 10) (concat "\\" digits))
((>= capture-count dec)
(error "backreference \\%s can't be used in Emacs regexps"
digits))
(t
;; from "man pcrepattern": if the
;; decimal number is greater than 9 and
;; there have not been that many
;; capturing subpatterns, PCRE re-reads
;; up to three octal digits following
;; the backslash, and uses them to
;; generate a data character. Any
;; subsequent digits stand for
;; themselves.
(goto-char (match-beginning 1))
(re-search-forward "[0-7]\\{0,3\\}")
(char-to-string (string-to-number (match-string 0) 8))))))
;; Regexp quoting.
("\\\\Q"
(let ((beginning (point)))
(search-forward "\\E")
(regexp-quote (buffer-substring beginning (match-beginning 0)))))
;; Various character classes
("\\\\d" "[0-9]")
("\\\\D" "[^0-9]")
("\\\\h" pcre-horizontal-whitespace)
("\\\\H" pcre-non-horizontal-whitespace)
("\\\\s" pcre-whitespace)
("\\\\S" pcre-non-whitespace)
("\\\\v" pcre-vertical-whitespace)
("\\\\V" pcre-non-vertical-whitespace)
;; Use Emacs' native notion of word characters
("\\\\[Ww]" (match-string 0))
;; Any other escaped character
("\\\\\\(.\\)" (regexp-quote (match-string 1)))
;; Any normal character
("." (match-string 0))))))
(push translated accum)))
(apply 'concat (reverse accum)))))
(defun pcre-re-or-class-token-to-elisp ()
"Consume the PCRE token at point and return its Elisp equivalent.
Handles only tokens which have the same meaning in character
classes as outside them."
(pcre-token-case
("\\\\a" (char-to-string #x07)) ; bell
("\\\\c\\(.\\)" ; control character
(char-to-string
(- (string-to-char (upcase (match-string 1))) 64)))
("\\\\e" (char-to-string #x1b)) ; escape
("\\\\f" (char-to-string #x0c)) ; formfeed
("\\\\n" (char-to-string #x0a)) ; linefeed
("\\\\r" (char-to-string #x0d)) ; carriage return
("\\\\t" (char-to-string #x09)) ; tab
("\\\\x\\([A-Za-z0-9]\\{2\\}\\)"
(char-to-string (string-to-number (match-string 1) 16)))
("\\\\x{\\([A-Za-z0-9]*\\)}"
(char-to-string (string-to-number (match-string 1) 16)))))
(defun pcre-char-class-to-elisp ()
"Consume the remaining PCRE character class at point and return its Elisp equivalent.
Point should be after the opening \"[\" when this is called, and
will be just after the closing \"]\" when it returns."
(let ((accum '("["))
(pcre-char-class-alternatives '())
(negated nil))
(when (looking-at "\\^")
(setq negated t)
(push "^" accum)
(forward-char))
(when (looking-at "\\]") (push "]" accum) (forward-char))
(while (not (looking-at "\\]"))
(let ((translated
(or
(pcre-re-or-class-token-to-elisp)
(pcre-token-case
;; Backslash + digits => always an octal char
("\\\\\\([0-7]\\{1,3\\}\\)"
(char-to-string (string-to-number (match-string 1) 8)))
;; Various character classes. To implement negative char classes,
;; we cons them onto the list `pcre-char-class-alternatives' and
;; transform the char class into a shy group with alternation
("\\\\d" "0-9")
("\\\\D" (push (if negated "[0-9]" "[^0-9]")
pcre-char-class-alternatives) "")
("\\\\h" pcre-horizontal-whitespace-chars)
("\\\\H" (push (if negated
pcre-horizontal-whitespace
pcre-non-horizontal-whitespace)
pcre-char-class-alternatives) "")
("\\\\s" pcre-whitespace-chars)
("\\\\S" (push (if negated
pcre-whitespace
pcre-non-whitespace)
pcre-char-class-alternatives) "")
("\\\\v" pcre-vertical-whitespace-chars)
("\\\\V" (push (if negated
pcre-vertical-whitespace
pcre-non-vertical-whitespace)
pcre-char-class-alternatives) "")
("\\\\w" (push (if negated "\\W" "\\w")
pcre-char-class-alternatives) "")
("\\\\W" (push (if negated "\\w" "\\W")
pcre-char-class-alternatives) "")
;; Leave POSIX syntax unchanged
("\\[:[a-z]*:\\]" (match-string 0))
;; Ignore other escapes
("\\\\\\(.\\)" (match-string 0))
;; Copy everything else
("." (match-string 0))))))
(push translated accum)))
(push "]" accum)
(forward-char)
(let ((class
(apply 'concat (reverse accum))))
(when (or (equal class "[]")
(equal class "[^]"))
(setq class ""))
(if (not pcre-char-class-alternatives)
class
(concat "\\(?:"
class "\\|"
(mapconcat 'identity
pcre-char-class-alternatives
"\\|")
"\\)")))))
I made a few minor modifications to a perl script I found on perlmonks (to take values from the command line) and saved it as re_pl2el.pl (given below). Then the following does a decent job of converting PCRE to elisp regexps, at least for non-exotic the cases that I tested.
(defun pcre-to-elre (regex)
(interactive "MPCRE expression: ")
(shell-command-to-string (concat "re_pl2el.pl -i -n "
(shell-quote-argument regex))))
(pcre-to-elre "__\\w: \\d+") ;-> "__[[:word:]]: [[:digit:]]+"
It doesn't handle a few "corner" cases like perl's shy {N,M}? constructs, and of course not code execution etc. but it might serve your needs or be a good starting place for such. Since you like PCRE I presume you know enough perl to fix any cases you use often. If not let me know and we can probably fix them.
I would be happier with a script that parsed the regex into an AST and then spit it back out in elisp format (since then it could spit it out in rx format too), but I couldn't find anything doing that and it seemed like a lot of work when I should be working on my thesis. :-) I find it hard to believe that noone has done it though.
Below is my "improved" version of re_pl2el.pl. -i means don't double escape for strings, and -n means don't print a final newline.
#! /usr/bin/perl
#
# File: re_pl2el.pl
# Modified from http://perlmonks.org/?node_id=796020
#
# Description:
#
use strict;
use warnings;
# version 0.4
# TODO
# * wrap converter to function
# * testsuite
#--- flags
my $flag_interactive; # true => no extra escaping of backslashes
if ( int(#ARGV) >= 1 and $ARGV[0] eq '-i' ) {
$flag_interactive = 1;
shift #ARGV;
}
if ( int(#ARGV) >= 1 and $ARGV[0] eq '-n' ) {
shift #ARGV;
} else {
$\="\n";
}
if ( int(#ARGV) < 1 ) {
print "usage: $0 [-i] [-n] REGEX";
exit;
}
my $RE='\w*(a|b|c)\d\(';
$RE='\d{2,3}';
$RE='"(.*?)"';
$RE="\0".'\"\t(.*?)"';
$RE=$ARGV[0];
# print "Perlcode:\t $RE";
#--- encode all \0 chars as escape sequence
$RE=~s#\0#\\0#g;
#--- substitute pairs of backslashes with \0
$RE=~s#\\\\#\0#g;
#--- hide escape sequences of \t,\n,... with
# corresponding ascii code
my %ascii=(
t =>"\t",
n=> "\n"
);
my $kascii=join "|",keys %ascii;
$RE=~s#\\($kascii)#$ascii{$1}#g;
#--- normalize needless escaping
# e.g. from /\"/ to /"/, since it's no difference in perl
# but might confuse elisp
$RE=~s#\\"#"#g;
#--- toggle escaping of 'backslash constructs'
my $bsc='(){}|';
$RE=~s#[$bsc]#\\$&#g; # escape them once
$RE=~s#\\\\##g; # and erase double-escaping
#--- replace character classes
my %charclass=(
w => 'word' , # TODO: emacs22 already knows \w ???
d => 'digit',
s => 'space'
);
my $kc=join "|",keys %charclass;
$RE=~s#\\($kc)#[[:$charclass{$1}:]]#g;
#--- unhide pairs of backslashes
$RE=~s#\0#\\\\#g;
#--- escaping for elisp string
unless ($flag_interactive){
$RE=~s#\\#\\\\#g; # ... backslashes
$RE=~s#"#\\"#g; # ... quotes
}
#--- unhide escape sequences of \t,\n,...
my %rascii= reverse %ascii;
my $vascii=join "|",keys %rascii;
$RE=~s#($vascii)#\\$rascii{$1}#g;
# print "Elispcode:\t $RE";
print "$RE";
#TODO whats the elisp syntax for \0 ???
The closest previous work on this have been extensions to M-x re-builder, see
http://www.emacswiki.org/emacs/ReBuilder
or the work of Ye Wenbin on PDE.
http://cpansearch.perl.org/src/YEWENBIN/Emacs-PDE-0.2.16/lisp/doc/pde.html
Possibly relevant is visual-regexp-steroids, which extends query-replace to use a live preview and allows you to use different regexp backends, including PCRE.