Haskell Types, Part II

Declaring Haskell Function Types

• Haskell, unlike Scheme, is statically-typed. (As opposed to dynamically-typed, like Scheme and JavaScript.) But there are no variables to declare as specific types, so what does this mean?

  Function parameters and return values

• Syntax:

  FunctionName :: ParamType -> Return Type
FunctionName :: ParamType -> Param2Type -> Param3Type -> Return Type

  Historical Note: This syntax is a variation on the common mathematical notation for indicating function types:

  FunctionName :: ParamType x Param2Type x Param3Type -> Return Type

  The form used by Haskell comes from a technique in combinatory logic called "currying": "the technique of translating the evaluation of a function that takes multiple arguments into evaluating a sequence of functions, each with a single argument." (Wikipedia article on Currying) Currying is named for a mathematician who was a contemporary of Alan Turing and Alonzo Church, named Haskell Curry. (Coincidence?)

• Do not have to declare types in Haskell. Haskell can infer types!