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Re: Parsing a language with optional spaces

From: John P. Hartmann
Subject: Re: Parsing a language with optional spaces
Date: Tue, 7 Jul 2020 10:55:12 +0200
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On 7/7/20 05:35, Akim Demaille wrote:
I believe you need to read again the documentation of /


It is not as simple as that. As I don't speak BASIC, let me rephrase this problem in FORTRAN IV which is also "blank agnostic":

DO <number> <variable> = <expression> , <expression> [, <expression>]

It is not until you reach the comma after the first expression that you know whether the statement is the beginning of a loop or it is an assignment. And the expression can contain commas in function calls, which defeats any trivial lookahead scanning. E.g.,

D O 17 6PQ R=FUN X(1 4, V 8)

is an assignment to variable DO176PQR. The function arguments can also be expressions that contain function calls.

As you can see, this more or less defeats any attempt to write a lex scanner. And you cannot just squeeze out all blanks in a front end because "Hollerith fields" can contain blanks that are significant (must remain).

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