| Copyright | © Frank Jung 2022-2025 |
|---|---|
| License | GPL-3 |
| Safe Haskell | Safe-Inferred |
| Language | Haskell2010 |
MyType
Description
Key Concepts Used
Type Applications
This feature allows you to explicitly specify types in your code using the
syntax. For example, typeName Int explicitly applies the type Int to the
function typeName.
Ambiguous Types
Ambiguous types occur when the type system cannot infer a type parameter because it is not used in a way that provides enough information. For example, in typeName, the type parameter a is only used in the phantom type of Proxy, which doesn't provide enough information for inference.
Scoped Type Variables
The ScopedTypeVariables extension allows type variables declared in a forall to be used explicitly within the function body.
Typeable
The Typeable typeclass provides runtime type information. The typeRep function retrieves a representation of a type that can be converted to a string.
Documentation
typeName :: forall a. Typeable a => String Source #
Proxy to record type. Proxy is equivalent to the unit type, (). But
also has a phantom type parameter a, which is used to keep track of
the type.
(Use type from Proxy)
data Proxy a = Proxy
Show ambigous types.
Hindley-Milner type system can only infer types to the right of the
context arrow (=>), which means the type parameter a can never be
correctly inferred. Haskell refers to such a type as ambiguous.
- Proxy @a
- Creates a Proxy value with the phantom type
a. A Proxy is a placeholder that carries type information but has no runtime value. - typeRep $ Proxy @a
- Retrieves the runtime representation of the type
ausingtypeRep. - show
- Converts the type representation to a string.
>>>typeName @Int"Int"
>>>typeName @String"[Char]"
>>>typeName @(Maybe [Int])"Maybe [Int]"