Am 05.09.2012 02:14, schrieb David Li:
Yes, what I was thinking is that there would be a "whitespace expansion"
step (probably after tokenization) that would convert statements like 2xy
into "2 x y" and then tokenize again
Multiple tokenization steps are usually not worth it.
Make it so that there's a token boundary between 2 and xy.
Splitting xy would be one of those things that need to be syntax-dependent.
SymPy allows defining variable names, so if there's an "x" and a "y",
you can split, and if there's an "xy", you wouldn't want to split.
If there are all three of "x", "y", and "xy", you have an ambiguous
parse; report that as something that the user needs to decide (ambiguous
parses are a fact of life for ad-hoc grammars, and in fact we need to
deal with these for other reasons anyway).
If SymPy provides you with a variable named "xy", add a temporary
grammar rule
xy ::= x y
and make each letter a separate token. (Temporary grammar rules and
ambiguities are anathema in the parser generators used for programming
languages, but they are no problem in the parser generators used for
natural languages. Different parsing technology.)
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