The essence of functional programming

摘要

This paper explores the use monads to structure functionalprograms. No prior knowledge of monads or category theory isrequired.

Monads increase the ease with which programs may be modified.They can mimic the effect of impure features such as exceptions,state, and continuations; and also provide effects not easilyachieved with such features. The types of a program reflect whicheffects occur.

The first section is an extended example of the use of monads. Asimple interpreter is modified to support various extra features:error messages, state, output, and non-deterministic choice. Thesecond section describes the relation between monads and thecontinuation-passing style. The third section sketches how monadsare used in a compiler for Haskell that is written in Haskell.