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Matthias Neubauer <neubauer@xxxxxxxxxxxxxxxxxxxxxxxxxx> writes:
> Matthias Neubauer <neubauer@xxxxxxxxxxxxxxxxxxxxxxxxxx> writes:
>
> Argh! I guess I got the stages wrong. Macros are more like ...
>
>
> # let prog = .< let x = 1 in
> .~ (let m () = let x = 2 in
> .< x >.
> in m ()) >.;;
> val prog : ('a, int) code = .<let x_2 = 1 in 2>.
> # let res = .! prog;;
> val res : int = 2
> #
>
>
> ... I guess.
That's still bogus because the macro application happens within the
same expression as the binding of the macro. The following looks more
appropriate:
# let prog = .< let x = 1 in
.~ (let m () = let x = 2 in
.< x >.
in
.< .~ (m ()) >.) >.;;
> Cross-stage persistence still kicks into action, though.
But you don't need it because a macro is a source-to-source
transformation and UNQUOTE (as SRFI-72 and MetaOCaml provide it)
already does the trick:
let prog = .< let x = 1 in
.~ (let m () = let x = .< 2 >. in
.< .~ x >.
in
.< .~ (m ()) >.) >.;;
Note that syntax-case also doesn't allow you to use bindings from the
meta-level within SYNTAX terms but provides a special abstraction for
this task: pattern variables.
--
Martin