<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html> <head> <!-- Generated by HsColour, http://www.cs.york.ac.uk/fp/darcs/hscolour/ --> <title>Control/Monad/Identity.hs</title> <link type='text/css' rel='stylesheet' href='hscolour.css' /> </head> <body> <pre><a name="line-1"></a><span class='hs-comment'>{- | <a name="line-2"></a>Module : Control.Monad.Identity <a name="line-3"></a>Copyright : (c) Andy Gill 2001, <a name="line-4"></a> (c) Oregon Graduate Institute of Science and Technology 2001, <a name="line-5"></a> (c) Jeff Newbern 2003-2006, <a name="line-6"></a> (c) Andriy Palamarchuk 2006 <a name="line-7"></a>License : BSD-style (see the file LICENSE) <a name="line-8"></a> <a name="line-9"></a>Maintainer : libraries@haskell.org <a name="line-10"></a>Stability : experimental <a name="line-11"></a>Portability : portable <a name="line-12"></a> <a name="line-13"></a>[Computation type:] Simple function application. <a name="line-14"></a> <a name="line-15"></a>[Binding strategy:] The bound function is applied to the input value. <a name="line-16"></a>@'Identity' x >>= f == 'Identity' (f x)@ <a name="line-17"></a> <a name="line-18"></a>[Useful for:] Monads can be derived from monad transformers applied to the <a name="line-19"></a>'Identity' monad. <a name="line-20"></a> <a name="line-21"></a>[Zero and plus:] None. <a name="line-22"></a> <a name="line-23"></a>[Example type:] @'Identity' a@ <a name="line-24"></a> <a name="line-25"></a>The @Identity@ monad is a monad that does not embody any computational strategy. <a name="line-26"></a>It simply applies the bound function to its input without any modification. <a name="line-27"></a>Computationally, there is no reason to use the @Identity@ monad <a name="line-28"></a>instead of the much simpler act of simply applying functions to their arguments. <a name="line-29"></a>The purpose of the @Identity@ monad is its fundamental role in the theory <a name="line-30"></a>of monad transformers. <a name="line-31"></a>Any monad transformer applied to the @Identity@ monad yields a non-transformer <a name="line-32"></a>version of that monad. <a name="line-33"></a>-}</span> <a name="line-34"></a> <a name="line-35"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Identity</span> <span class='hs-layout'>(</span> <a name="line-36"></a> <span class='hs-keyword'>module</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Functor</span><span class='hs-varop'>.</span><span class='hs-conid'>Identity</span><span class='hs-layout'>,</span> <a name="line-37"></a> <a name="line-38"></a> <span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-layout'>,</span> <a name="line-39"></a> <span class='hs-keyword'>module</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Fix</span><span class='hs-layout'>,</span> <a name="line-40"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span> <a name="line-41"></a> <a name="line-42"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span> <a name="line-43"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span><span class='hs-varop'>.</span><span class='hs-conid'>Fix</span> <a name="line-44"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Functor</span><span class='hs-varop'>.</span><span class='hs-conid'>Identity</span> </pre></body> </html>