Haskell Fundamentals

Haskell is a statically typed, purely functional programming language. You describe values and relationships with expressions instead of changing variables through a sequence of statements. The compiler checks how types fit together before the program runs.

Three ideas shape the language:

Pure functions return results without changing hidden state.
Types describe which values an expression accepts and returns.
Lazy evaluation computes an expression when its result is needed.

These ideas reinforce one another. Purity makes an expression easier to reason about because the same inputs produce the same result. Types expose important boundaries. Lazy evaluation lets you separate the description of a value from the moment its parts are computed.

Expressions and functions

Almost everything you write is an expression with a value. A function applies to an argument without parentheses:

double x = x * 2
result = double 21

Haskell Fundamentals

Expressions and functions

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