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Custom Types

Creating data types and re-naming types is powerful. To achieve both things, PureScript offers two keywords: Using "Type" we can alias existing types. Using "Data" we can define custom data types.

type keyword​

This keyword helps to reference existing data types.

type MultipleChars = String

someString :: MultipleChars
someString = "Hello world"

It is also used to create the type definition for records and other complex structures.

data keyword​

The data keyword is a little bit more complex. On the left-hand side, we have the actual data type. On the right-hand side of the equals-sign is the so-called data constructor. Custom data types must always start with an uppercase letter.

data MyDataType = MyDataType

Default types like Boolean can be written with the data keyword, even though this will collapse with the existing type.

data Boolean = True | False