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lpeg.Cb

Summary

Creates a back capture

Prototype

lpeg.Cb (name)


Description

This pattern matches the empty string and produces the values produced by the most recent group capture named name.

Most recent means the last complete outermost group capture with the given name. A Complete capture means that the entire pattern corresponding to the capture has matched. An Outermost capture means that the capture is not inside another complete capture.

For example:

open = "[" * lpeg.Cg(lpeg.P"="^0, "init") * "[" * lpeg.P"\n"^-1
close = "]" * lpeg.C(lpeg.P"="^0) * "]"
closeeq = lpeg.Cmt(close * lpeg.Cb("init"), function (s, i, a, b) return a == b end)
string = open * m.C((lpeg.P(1) - closeeq)^0) * close /
function (o, s) return s end

The open pattern matches [=*[, capturing the repetitions of equal signs in a group named init; it also discharges an optional newline, if present. The close pattern matches ]=*]. The closeeq pattern first matches close; then it uses a back capture to recover the capture made by the previous open, which is named init; finally it uses a match-time capture to check whether both captures are equal. The string pattern starts with an open, then it goes as far as possible until matching closeeq, and then matches the final close. The final function capture simply consumes the captures made by open and close and returns only the middle capture, which is the string contents.


See Also ...

Lua functions

lpeg.B - Matches patt n characters behind the current position, consuming no input
lpeg.C - Creates a simple capture
lpeg.Carg - Creates an argument capture
lpeg.Cc - Creates a constant capture
lpeg.Cf - Creates a fold capture
lpeg.Cg - Creates a group capture
lpeg.Cmt - Creates a match-time capture
lpeg.Cp - Creates a position capture
lpeg.Cs - Creates a substitution capture
lpeg.Ct - Creates a table capture
lpeg.locale - Returns a table of patterns matching the current locale
lpeg.match - Matches a pattern against a string
lpeg.P - Converts a value into a pattern
lpeg.print - Outputs debugging information to stdout
lpeg.R - Returns a pattern that matches a range of characters
lpeg.S - Returns a pattern that matches a set of characters
lpeg.setmaxstack - Sets the maximum size for the backtrack stack
lpeg.type - Tests if a value is a pattern
lpeg.V - Creates a non-terminal variable for a grammar
lpeg.version - Returns the LPeg version

Topics

Lua bc (big number) functions
Lua bit manipulation functions
Lua LPEG library
Lua package functions
Lua PCRE regular expression functions
Lua script extensions
Lua string functions
Lua syntax
Lua table functions
Lua utilities
Regular Expressions
Scripting
Scripting callbacks - plugins

(Help topic: lua=lpeg.Cb)

Documentation contents page


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