List Literal Patterns

[martin-ilgner]

Starting to implement #821

[jiribenes]

This doesn't (yet?) do the .. part of the issue #821, so we can't match on tails :(

and I'd like to see a few more pos tests like if ([None(), Some(42) is [head, Some(x)]) { ... } and with val [x, y] = foo { ... } and foo { case [x, y, z, a] => ... } :)

[martin-ilgner]

• how do we make sure that there's only one "tail" pattern? where's the latest we can fail here

I made it so that after a tail pattern, ] is expected

• do we add it as a token, or "just" eat two . tokens?

There is already a .. token

• what's case [..rest] => ...? error or the whole list?

Whole list, why not

• how do we write an ignored splat? can we just write [head, ..] or do we need [head, .._]?

Write [head, ..]

• trailing commas?

Not after a splat. (Could change this, but I think there is no argument for it, as splat is always last)

[martin-ilgner]

What do you mean with with val [x, y] = foo { ... }? Is it even possible/not a compile error because length of list is unknown? Maybe I could do val [x, ..y] = lst

[martin-ilgner]

@jiribenes

[jiribenes]

What do you mean with with val [x, y] = foo { ... }? Is it even possible/not a compile error because length of list is unknown?

Ah, sorry, you can do val-else (val [x, y] = foo { ... } else panic("ohno")) and with-val-else :)

effekt/examples/pos/with_val_and_else.effekt

Lines 20 to 26 in 1bae57f

	with val obj
	and obj is Dict(fields)
	and fields.lookup("user") is Some(userObj)
	and userObj is Dict(userFields)
	and userFields.lookup("name") is Some(String(name))
	and userFields.lookup("age") is Some(Number(age))
	= data() else None()

[martin-ilgner]

I also rewrote manyTrailing. Should be enough pos tests for now 🙏