# DocTest

From HaskellWiki

Revision as of 12:00, 22 March 2009 by SimonHengel (talk | contribs)

## What is DocTest

DocTest is a small program, that checks examples in Haskell comments. It is modeled after doctest for Python.

## Tutorial

Bellow is a small Haskell module. The module contains source code comments. Those comments are examples from an interactive Haskell session and demonstrate how the module is used.

```
module Fib where
-- Examples:
--
-- > fib 10
-- 55
-- > fib 5
-- 5
fib 0 = 0
fib 1 = 1
fib n = fib (n - 1) + fib (n - 2)
```

With DocTest you may checks if the implementation satisfies the given examples, by typing (on your Unix shell):

$ doctest Fib.hs

Lines starting with `-- >`

denote *expressions*.
All comment lines following an expression denote the
*result* of that expression. Result is defined by what a REPL
(e.g. ghci) prints to `stdout`

and `stderror`

when
evaluating that expression.

## DocTest on Hackage

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/DocTest