MUSHclient documentation: lpeg.Cb

lpeg.Cb

lpeg.Cb
Lua function 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 ... 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 table functions Lua utilities Regular Expressions Scripting Lua functions 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.type (Tests if a value is a pattern) lpeg.V (Creates a non-terminal variable for a grammar) lpeg.version (Returns the LPeg version) (Help topic: lua=lpeg.Cb) Documentation contents page

Lua function

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.