Allow multiple patterns with %, e.g. (% x y = (f) (z . t) = (g x) in … or (w) = (h y) in … #2

New Issue

2016-04-14T00:41:08+01:00

SuzanneSoy commented

2016-04-14 00:41:08 +01:00

(Migrated from github.com)

The % i.e. let … in … form could support several cases, a match does. The general syntax would be (let (~seq or (~seq bindings … = expr) … (~optional in) body …) …), with the first or optional. If the form directly starts with or without any binding nor body, then it should not consider that there is a successful empty match with an empty body at the beginning, but instead just strip the first or. If empty bodies were allowed, to have an empty match (which will always succeed and therefore make what follows dead code), one could write (let in or dead-variables = (dead-code) in dead-code) to disambiguate.

Here is an example use:

(% x y = (f)
   (z . t) = (g x)
   in
   <code>
   or
   (w) = (h y)
   in
   <code>

The `%` i.e. `let … in …` form could support several cases, a `match` does. The general syntax would be `(let (~seq or (~seq bindings … = expr) … (~optional in) body …) …)`, with the first `or` optional. If the form directly starts with `or` without any binding nor body, then it should _not_ consider that there is a successful empty match with an empty body at the beginning, but instead just strip the first `or`. If empty bodies were allowed, to have an empty match (which will always succeed and therefore make what follows dead code), one could write `(let in or dead-variables = (dead-code) in dead-code)` to disambiguate. Here is an example use: ``` racket (% x y = (f) (z . t) = (g x) in <code> or (w) = (h y) in <code> ```

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