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Parsing > Parser > optionalSignParser

optionalSignParser -- a parser that accepts an optional plus sign or minus sign

Description

The return value is either 1 or -1, depending on the indicated sign.

i1 : (optionalSignParser @ constParser "abc" : charAnalyzer) "abc"

o1 = (1, abc)

o1 : Sequence

i2 : (optionalSignParser @ constParser "abc" : charAnalyzer) "+abc"

o2 = (1, abc)

o2 : Sequence

i3 : (optionalSignParser @ constParser "abc" : charAnalyzer) "-abc"

o3 = (-1, abc)

o3 : Sequence

Code

/usr/share/Macaulay2/Parsing.m2:157:31-157:135: --source code:
optionalSignParser = Parser(c -> if c === null then 1 else if c === "-" then terminalParser(-1) else if c === "+" then terminalParser 1)

See also

Parser @ Parser -- parser conjunction
constParser -- produce a parser that accepts a fixed string, one character at a time
charAnalyzer -- a lexical analyzer that provides characters from a string one at a time
Parser : Analyzer -- combine a parser with a lexical analyzer to make a complete system

For the programmer

The object optionalSignParser is a parser.