Re: Languages with optional spaces

On 29/02/2020 11:48, Christopher F Clark wrote:
> "Ev. Drikos" <drikosev@gmail.com> posted an interesting albeit partial solution
> to the problem of keywords being part of identifiers in languages with
> optional spaces.


It's only an example for the beginning of statements, based on the
description I read in other postings. It couldn't be the solution of
an unspecified problem. The terms "usually" & "in theory" aren't specs.


In contrast, one who wants to code a parser for the particular dialect
of BASIC should know ie what the 6502 or the Compukit UK101 code did.


> The problem is that some keywords can appear at places other than the
> beginning of an identifier.
> In fact, in the worst case scenario, the language can be ambiguous.
>...
>
> With a GLR parser (or something equivalent in power, e.g. an Earley
> parser or CYK) and a lexer that returns all possible sets of
> tokenizations one can find all the relevant parse trees and then see
> if only 1 makes semantic sense.


Obviously, those who coded such BASIC parsers had some simpler rules,
ie the position of the first 'TO' might be used for the statement 50.
Such ruling may comply with the description given by Dr Martin Ward.


Ev. Drikos

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