Match expressions

[huonw]

@bjz, r?

Rusp Repl
> (def foo (fn (a b)
+   (match a
+     (1 b)
+     ("bar" (+ b 1))
+     ((1 2) (+ b 2))
+     ((x .. y) y))))
()
> (foo 1 2)
2
> (foo 1 3)
3
> (foo "bar" 3)
4
> (foo (list 1 2) 3)
5
> (foo (list 3 2) 3)
(2)
> (foo (list 3 2 4 5) 3)
(2 4 5)

[huonw]

It doesn't do much validation of the patterns, beyond what would make them totally unusable (i.e. not fns or macros in a pattern), so something like (match ... ((a a) (+ 1 2)) ...) will run perfectly well, despite double-binding a.

[brendanzab]

Neat! Could we use this to implement fn matching?

[huonw]

That was the plan, although it may require some syntactic changes.