Good afternoon!
Macro newbie here,
I wanted to define a macro $: so that I could write this:
(cond
[$: p (Point x y) => (+ x y)])
and it would expand into this:
(cond
[(if (Point? p) p #f)
=> (match-lambda [(Point x y) (+ x y)])]
[else #f])
I gave it a try:
(define-syntax ($: stx)
(syntax-case stx (=>)
[(_ arg (struct-name field ...) => body)
(with-syntax ([pred? (format-id stx "~a?" #'struct-name)])
#'[(if (pred? arg)
arg
#f)
=>
(match-lambda ([(struct-name field ...) body]))])]))
But this macro expands (or attempts to) after cond has expanded... which is
not what I wanted.
Is there a quick fix for this? Or can someone point me towards a particular
spot in the documentation where I might educate myself?
I know about match (we're great friends)---I was just toying around with
this to see if I could get cond to look pretty w/ structs as well.
Best,
Andrew
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