Good question! The trick is that `match` is passed an (n-ary) Haskell function on embedded terms (in the example hidden as a lambda-case) which it can continually re-apply, forcing every case alternative to succeed in turn so that we can explore the right-hand-side of each equation. This is necessary because we have staged compilation; the Haskell case statement is being resolved at an earlier stage (and possibly on a different device) than when we find out which branch actually succeeds. I think it's an interesting use case for explicitly bi-directional pattern synonyms which I haven't seen before. -T On Tue, 1 Sep 2020 at 15:39, Emil Axelsson <78emil@gmail.com> wrote:
Nice! How is that done?
/ Emil
Den 2020-09-01 kl. 13:50, skrev Trevor McDonell:
Embedded pattern matching
This release also introduces support for *embedded pattern matching* via the new match operator, which allows us to reuse Haskell's case syntax in embedded code:
intersect :: Exp Ray -> Exp Object -> Exp Bool intersect ray = match \case Sphere_ c r -> ... Triangle_ a b c -> ...