Enum tag destructuring #1813
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Enum tag destructuring #1813
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Until now, only enum variants were supported within patterns (applied enums). This commit adds support for bare enum tags as well.
Make `typeof` returns `'Enum` for enum variants as well, and update `std.contract.Equal` to properly handle enum tags and enum variants.
jneem
approved these changes
Feb 12, 2024
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Follow-up of #1812. Prior to extending match expressions with full pattern matching, this PR adds support for bare enum tags, which will be needed to be able to handle the existing enum tags match expressions.
In the end, I tend to agree with @vkleen 's comment, and contrary to what the original description of #1812 said, enum tags shouldn't in fact be treated as constants but rather as special cases of enum variants. It'll also make the transition easier, if we decide to go with an explicit
Unittype and really have them be the same thing.There is a bit of fuss around lazyness for patterns. Right now,
let 'Foo x = <exp> in <body>doesn't fire any check if<body>doesn't usex, which is in line with lazy contracts, but might be surprising. Then what should do a pattern that doesn't bind any variable? In this PR, I went with the answer that we should add an artificial dependency (basically,seq), otherwiselet 'Foo = x in <body>would always succeed, whateverxis, which is unreasonable.Thinking ahead toward pattern in match expression, patterns will have to evaluate arguments up to a point to decide which branch to take (and hence be more eager than current destructuring patterns). Although it's technically backward-incompatible, I think we should do the same with destructuring. Some programs that use to evaluate might suddenly break, but it's arguably a "should have broke earlier" case - adding eagerly error reporting isn't the same as breaking entirely fine programs. If we do so, we can just get rid of those lazyness shenanigans.
But we can discuss this question further.