Hello,
Infix in Scheme is all the rage these days. ;-) Awhile back I mentioned
an 'alg' procedure which converts a string containing an infix
expression to an sexp. So for example:
> (import (numero symbolic alg))
> (alg "x+y")
(+ x y)
> (alg "f(x,y)+z")
(+ (f x y) z)
>
I'd like to have a macro version of alg which expands to the sexp at at
"expansion time" (what's the right terminology here?).
Here's a version which seems to work in simple cases. I wanted to run it
by y'all though; does it look correct? Any advice?
(define-syntax algm
(lambda (stx)
(syntax-case stx ()
( (algm expr)
(with-syntax ((new-expr (datum->syntax
(syntax algm)
(alg (syntax->datum (syntax expr))))))
(syntax new-expr)) ))))
Example; let's say we try the "x+y" where those symbols aren't bound. We
should get an error:
> (algm "x+y")
Unhandled exception
...
>
Try the same expression, but in a context where the symbols have values:
> (let ((x 10)
(y 20))
(algm "x+y"))
30
>
Ed
