Regular Expression Utilities

The script system\packages\regex\regbuild.ijs contains definitions to for building regular expression patterns.

Many of the verbs below may enclose its argument in parentheses (to make it a subexpression). For example,
anyof 'abc' returns '(abc)*'.

The argument is only put in parentheses if necessary.
anyof set 'abc' is '[abc]*'.

The following verbs correspond directly to a feature of the regular expression notation:

set chars	returns set construction for chars
set 'abc'
[abc]

not chars	set of non-matching chars
set not 'abc'
[^abc]

sub pat	make a subexpression
set 'abc'
(abc)

someof pat	pattern matching 1 or more pat
someof 'abc'
(abc)+

(min,max) of pat	pattern matchin min up to max of pat
2 4 of 'abc'
(abc){2,4}

pat1 or pat2	pattern matching either pat1 or pat2
'abc' or 'd'
abc|x

pat1 or pat2	pattern matching pat1 immediately followed by pat2
'action=' by 'move' or 'copy'
action=(move|copy)

sub pat	makes pat a subexpression
sub 'abc'
(abc)

bkref refnum	back-reference to a previous subexpression
bkref 1
\1

Some nouns can be used as parts of regular expressions:

white

owhite

sol

eol

any

Finally, some miscellaneous verbs

plain text	returns a regular expression matching the plain text
plain 'dir j.*'
dir j\.\*

pat1 between y	result is elements of y catenated together with pat1 between each
' *' between 'abc'
a *b *c ' *' between 'p1';'p2';'p3|p4'
p1 *p2 *(p3|p4)

comment nb pattern

add comment to pattern

Interpretation of a pattern always stops at the first null character (0{a.). The nb verb makes use of this by catenating a null character and comment at the end of a pattern.

   p=. rxcomp 'some digits' nb '[[:digit:]]+'
   rxinfo p
+-+----------------------------+
|1|[[:digit:]]+ NB. some digits|
+-+----------------------------+

setchars setpat

   setchars '[a-d[:digit:]]'

0123456789abcd

Character classes

The following nouns are strings which are used within sets to specify a character class:

   alnum, alpha, blank, cntrl, digit, graph,
   lower, print, punct, space, upper, xdigit

For example,

   alpha=. '[:alpha:]'

Corresponding nouns, named with a leading uppercase, are patterns specifying a set of the character class, for example,

   Alpha=. '[[:alpha:]]'    NB.  (same as    set alpha)

J patterns

The following nouns, defined in packages\regex\regj.ijs , are patterns which match elements of J code:

Jname	matches a J name
Jnumitem, Jnum	matches a J numeric item or array (constant)
Jchar	matches a J character string
Jconst	matches a J numeric or character constant, include a. and a:
Jgassign, Jlassign, Jassign	matches J global, local, or either assignment
Jlpar, Jrpar	match J's left and right parentheses
Jsol, Jeol	match the start or end of a J sentence (ignores leading blanks and trailing blanks/comments)