= 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-match]]
==== match(string, 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.
[[proc-find]]
==== find(string, Regex, start = 0, endpos = -1): RegexMatch
Finds the given pattern in the string. Bounds work the same as for
link:#proc-match[`match(...)`], but instead of being anchored to the start of
the string, it can match at any point between `start` and `endpos`.
[[iter-find]]
==== 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-match[`match(...)`]
Variants:
- `findAll(...)` returns a `seq[RegexMatch]`
- `findAllStr(...)` returns a `seq[string]`
[[proc-split]]
==== split(string, Regex): 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", ""]`.
[[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: `$$`.
=== 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).asTable` :: returns a table with each named capture
as a key.
`(captureBounds|capture).toSeq` :: returns all the captures by their number.
=== Pattern
Represents the pattern that things are matched against, constructed with
`initRegex(string)` or `re(string)`. Examples: `re"foo"`, `re(r"foo # comment",
"Sx<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
- `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:
[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