Re: [Caml-list] Again on pattern matching and strings

[Alessandro Baretta <alex@baretta.com>]

Daniel de Rauglaudre wrote:
> Hi,
> 
> In this case, the <ident> is added as keyword in the grammar,
> evaluated at parse time, transformed into the <expression/pattern>
> depending on its position. The possible parameters are possibly
> substituted by their actual value in the expression pattern.

Does "evaluated at parse time" mean that you define a syntax 
tree transformation as opposed to a character stream 
transformation? I ask because I'd like this scheme to avoid 
the bug-prone interactions between C macros and surrounding 
code.

> ...We can have also:
>      UNDEFMACRO <ident>
> 
> To remove it from the grammar.

This is more or less what I had in mind. The only problem 
with this scheme is probably with compile-time error 
reporting. If this is not somehow linked with the compiler, 
how will the compiler be able to tell us that that something 
we wrote makes no sense? If the macro is small and self 
evident, this might not be a problem, but if you use such 
macros to match, for example, the Epson ESC/P command set, 
drawing a connection between a compiler error--reported with 
reference to the pure Caml syntax tree--and the 
CamlP4-extended source code might be difficult.

In all other respects, this approach seems to be satisfactory.

> Would it be OK? General enough? Other propositions?
> 


Thank you,
Alex

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