= NRE

== What is NRE?

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

== Why?

The http://nim-lang.org/re.html[re.nim] module that http://nim-lang.org/[Nim]
provides in its 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 https://ideone.com/dDMjmz[Perl],
   http://jsfiddle.net/xtcbxurg/[Javascript], and
   https://ideone.com/hYJuJ5[Java]'s precedent of returning a list of each
   character (`"123".split(re"") == @["1", "2", "3"]`).

== Documentation

=== Operations

[[proc-find]]
==== find(string, Regex, start = 0, endpos = -1): RegexMatch

Finds the given pattern in the string between the end and start positions.

`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.

[[proc-match]]
==== match(string, Regex, start = 0, endpos = -1): RegexMatch

Like link:#proc-find[`find(...)`], but anchored to the start of the string.
This means that `"foo".match(re"f") == true`, but `"foo".match(re"o") ==
false`.

[[iter-find]]
==== iterator findIter(string, Regex, start = 0, endpos = -1): RegexMatch

Works the same as link:#proc-find[`find(...)`], but finds every non-overlapping
match. `"2222".find(re"22")` is `"22", "22"`, not `"22", "22", "22"`.

Arguments are the same as link:#proc-find[`find(...)`]

Variants:

 - `proc findAll(...)` returns a `seq[RegexMatch]`
 - `proc findAllStr(...)` returns a `seq[string]`

[[proc-split]]
==== split(string, Regex, maxsplit = -1): seq[string]

Splits the string with the given regex. This works according to the rules that
Perl and Javascript use.

  - If the match is zero-width, then the string is still split:
    `"123".split(r"") == @["1", "2", "3"]`.
  - If the pattern has a capture in it, it is added after the string split:
    `"12".split(re"(\d)") == @["", "1", "", "2", ""]`.
  - If `maxsplit != -1`, then the string will only be split `maxsplit` times.
    `"1.2.3".split(re"\.", maxsplit = 1) == @["1", "2.3"]`

[[proc-replace]]
==== replace(string, Regex, sub): string

Replaces each match of Regex in the string with `sub`.

If `sub` is a `proc (RegexMatch): string`, then it is executed with each match
and the return value is the replacement value.

If `sub` is a string, then each match is replaced with that string, where the
captures are accessable as `$1`, `$2`, and so on. A literal `$` can be added by
doubling up like so: `$$`.

[[proc-escapere]]
==== escapeRe(string): string

Escapes the string so it doesn't match any special characters. Incompatible
with the Extra flag (`X`).

=== RegexMatch

Represents the result of an execution. On failure, it is `nil`. The available
fields are as follows:

`pattern: Regex` :: the pattern that is being matched
`str: string` :: the string that was matched against
`captures[]: string` :: the string value of whatever was captured
at that id. If the value is invalid, then behavior is undefined. If the id is
`-1`, then the whole match is returned. If the given capture was not matched,
`nil` is returned.
 - `"abc".match(re"(\w)").captures[0] == "a"`
 - `"abc".match(re"(?<letter>\w)").captures["letter"] == "a"`
 - `"abc".match(re"(\w)\w").captures[-1] == "ab"`
`captureBounds[]: Option[Slice[int]]` :: gets the bounds of the
given capture according to the same rules as the above. If the capture is not
filled, then `None` is returned. The upper bound is exclusive, the lower bound
is inclusive.
 - `"abc".match(re"(\w)").captureBounds[0] == 0..1`
 - `"abc".match(re"").captureBounds[-1] == 0..0`
 - `"abc".match(re"abc").captureBounds[-1] == 0..3`
`match: string` :: the full text of the match.
`matchBounds: Slice[int]` :: the bounds of the match, as in `captureBounds[]`
`(captureBounds|captures).toTable` :: returns a table with each named capture
as a key.
`(captureBounds|captures).toSeq` :: returns all the captures by their number.
`$: string` :: same as `match`

=== Pattern

Represents the pattern that things are matched against, constructed with
`re(string, string)`. Examples: `re"foo"`, `re(r"foo # comment",
"x<anycrlf>")`. 

`pattern: string` :: the string that was used to create the pattern.
`captureCount: int` :: the number of captures that the pattern has.
`captureNameId: Table[string, int]` :: a table from the capture names to
   their numeric id.

==== 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
 - `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:
[quote, , man pcre]
____
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
 - `<no_study>` - turn off studying; study is enabled by deafault