Re: Languages that are hard to parse

glen herrmannsfeldt wrote:


> Hans-Peter Diettrich wrote:
> (snip)
>
>>IMO new programming languages are designed for easy parsing, by using
>>either a grammar based parser generator, or in handwritten code
>>without a (proven) grammar. Derivates of "un-formal" legacy languages,
>>like C, fall into their own category (homebrew trouble, dead end ;-)
>
>
> Not exactly counterexamples, but Fortran and PL/I don't seem to have
> been designed to be easy to parse, and as I understand it from people
> working with them, they aren't.


Not really as much of a problem as it's said to be. Naturally a
top-down or recursive-descent parser is impossible, but otherwise it's
quite clean.
....


> [Fortran is actually pretty easy to parse. It's the lexer that's hard since
> spaces don't matter (or didn't until recent versions of Fortran.) I gather
> that PL/I isn't all that hard to parse once you do some hackery (not unlike
> Fortran's) to decide whether a statement is an assignment or starts with a
> keyword. It's just bulky. -John]


You just need to do look-ahead. If I were starting from scratch I'd
just pull in the whole program and then parse. As it is I did a bit
more work because some of my code does a partial parse of an expression
as tokens are read, when it would be simpler to just wait until a whole
statement has been read before parsing.

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