N___ RegEx Library

What is NRE?

A new regular expression library for Nim using PCRE to do the hard work.

Why?

The re.nim module that Nim provides in it's standard library is inadequate:

• It provides only a limited number of captures, while the underling library (PCRE) allows an unlimited number.
• Instead of having one proc that returns both the bounds and substring, it has one for the bounds and another for the substring.
• If the splitting regex is empty (""), then it returns the input string instead of following Perl, Javascript, and Java's precedent of returning a list of each character ("123".split(re"") == @["1", "2", "3"]).

Documentation

Construction

Creating a pattern is easy: re"([0-9]+)". By default, the extended flag is passed in order to encourage readable expressions, so [0-9]+ is equivalent to [0-9] + # foo. If you'd like to pass your own flags, then re(r"([0-9]+)", "<flags>") will work. Here is a list of the available flags:

• 8 - treat both the pattern and subject as UTF8
• 9 - prevents the pattern from being interpreted as UTF, no matter what
• A - as if the pattern had a ^ at the beginning
• E - DOLLAR_ENDONLY
• f - fails if there is not a match on the first line
• i - case insensitive
• m - multi-line, ^ and $ match the beginning and end of lines, not of the subject string
• N - turn off auto-capture, (?foo) is necessary to capture.
• s - . matches newline
• S - study the pattern to hopefully improve performance. JIT is unspported at the moment.
• U - expressions are not greedy by default. ? can be added to a qualifier to make it greedy.
• u - same as 8
• W - Unicode character properties
• X - "Extra", character escapes without special meaning (\w vs. \a) are errors
• x - extended, comments (#) and newlines are ignored (extended)
• Y - pcre.NO_START_OPTIMIZE,
• <cr> - newlines are separated by \r
• <crlf> - newlines are separated by \r\n (Windows default)
• <lf> - newlines are separated by \n (UNIX default)
• <anycrlf> - newlines are separated by any of the above
• <any> - newlines are separated by any of the above and Unicode newlines:

single characters VT (vertical tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit library, the last two are recognized only in UTF-8 mode.

• <bsr_anycrlf> - \R matches CR, LF, or CRLF
• <bsr_unicode> - \R matches any unicode newline
• <js> - Javascript compatibility

Sx is enabled by default in order to encourage use of whitespace for better readability.

Usage

proc match(str: string, pattern: Regex, start = 0, endpos = -1): RegexMatch

Tries to match the pattern, starting at start. This means that "foo".match(re"f") == true, but "foo".match(re"o") == false.

• start
  • The start point at which to start matching. |abc is 0; a|bc is 1
• endpos
  • The maximum index for a match; -1 means the end of the string, otherwise it's an exclusive upper bound.