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Wipple's updated type syntax

November 17, 2021

In my spree to streamline different parts of Wipple, I’ve decided to update the type syntax to be more flexible and consistent. Here’s how it works!

The first change is that all values can be used in type position now. The type of the value is used, sort of like an implicit typeof operator. For example:

x : 42
f : n :: x -> n

Here, n has type Number. Note that this paves the way for constants as types (eg. x :: 42)!

The second change is that data and enum no longer return types! Instead, they return “forms” that expand to a value or type depending on where they are used. I already use the form pattern throughout the Wipple compiler, so this is an easy change to make. To the user, this means that data and enum effectively return “constructor” values that can be used in type position or value position.

Integer : data ...

x : Integer 42 -- as a value
f : n :: Integer -> n -- as a type

The third change is that for now accepts a where clause that checks for the existence of traits:

show :: for A where (Show A) -> A -> Text

This is much better than the previous Show :: A -> _ syntax, and puts Wipple more in line with Haskell!

In addition, pattern syntax has been extended to support datatypes and traits:

Single : data Number

Fields : data {
foo :: Number
bar :: Text

Trait : for A -> trait A -> A

Single n : Single 42

Fields { foo bar } : Fields {
foo : 42
bar : "hello"

Trait Number : n -> n

Notice that datatypes take their variables, while traits take their type parameters.

The final change is that for may only be applied once per expression (ie. it may not be nested), and that type parameters in traits must be filled explicitly as done above. This makes it easier to typecheck things, and shouldn’t really even be noticeable.

Stay tuned for more updates!

© 2023 Wilson Gramer