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javascriptregexpegpegjs

Test all alternative patterns in PEG.js

I want to use PEG.js to recognize numbers in a few different formats:

number = integer
/ real
/ (integer/real) '^' (integer/real)
/ (integer/real) '^^' (integer/real)

real = [0-9]+ '.' [0-9]*
/ [0-9]* '.' [0-9]+

integer = [0-9]+

PEG.js does not look for alternatives if there is a partial match earlier in the sequence of alternatives. Most numbers start with an integer, and if they don't they start with a real number. How can I rewrite this so that it tests each alternative individually? (I am not interested in compounding the rules into fewer rules.)

Solution

  • Try matching more specific expressions first (because there's overlap between the rules, so you want PEG to match more specifically first to prevent partial matches):

    number = ( real / integer ) '^' ( real / integer )
/  ( real / integer ) '^^' ( real / integer )
/ real
/ integer