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.

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