TypeCompose
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(Category:Applicative > Applicative Functor) 

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+  [[Category:Composition]] 

+  [[Category:Applicative Functor]] 

+  [[Category:Libraries]] 

+  [[Category:Packages]] 

+  [[Category:Typelevel programming]] 

+  
== Abstract == 
== Abstract == 

−  '''TypeCompose''' provides some classes & instances for forms of type composition. It also includes a very simple implementation of datadriven computation. 
+  '''TypeCompose''' provides some classes & instances for forms of type composition, as well as some modules that haven't found another home. 
−  * Read [http://darcs.haskell.org/packages/TypeCompose/doc/html the Haddock docs] (with source code, additional examples, and Comment/Talk links). 
+  Besides this wiki page, here are more ways to find out about TypeCompose: 
−  * Get the code repository: '''<tt>darcs get http://darcs.haskell.org/packages/TypeCompose</tt>''', or 
+  * Visit the [http://hackage.haskell.org/cgibin/hackagescripts/package/TypeCompose Hackage page] for library documentation and to download & install. 
−  * Grab a [http://darcs.haskell.org/packages/TypeCompose/dist distribution tarball]. 
+  * Or install with <tt>cabal install TypeCompose</tt>. 
−  * See the [http://darcs.haskell.org/packages/TypeCompose/CHANGES version changes]. 
+  * Get the code repository: <tt>darcs get http://code.haskell.org/~conal/code/TypeCompose</tt>. 
−  +  <!* See the [[TypeCompose/Versions version history]].> 

−  TypeCompose is used in [[Phooey]], a functional GUI library. 

== Type composition == 
== Type composition == 

−  For now, see the [http://darcs.haskell.org/packages/TypeCompose/doc/html/ControlCompose.html Haddock docs]. 
+  The <hask>Control.Compose</hask> module includes 
+  * Various type compositions (unary/unary, binary/unary, etc). Most are from [http://www.soi.city.ac.uk/~ross/papers/Applicative.html Applicative Programming with Effects]. In particular, <hask>g `O` f</hask> composes functors in to functors and applicative functors (AFs) into AFs. (In contrast, monads do not in general compose.) Composition makes AFbased programming simple and elegant, partly because we don't need an AF counterpart to monad transformers. 

+  * Cofunctors (contravariant functors). Great for "consumer" types, just as functors suit "producer" (container) types. There are several composition options. 

+  * Type argument flip. Handy for cofunctors: use <hask>Flip (>) o</hask>, for <hask>(> o)</hask>. 

+  * Constructor in pairs: <hask>(f a, g a)</hask>. 

+  * Constructor in arrows/functions: <hask>f a ~> g a</hask>. 

+  
+  == Other features == 

+  
+  === Composable bijections === 

+  
+  Given all the type constructors and compositions of them, I found myself writing some pretty awkward code to wrap & unwrap through multiple layers. Composable bijections help a lot. 

+  
+  The <hask>Data.Bijection</hask> module is inspired by [http://citeseer.ist.psu.edu/alimarine05there.html There and Back Again: Arrows for Invertible Programming], though done here in a less general setting. 

+  
+  === Pair & functionlike types === 

+  
+  The <hask>Data.Zip</hask> and <hask>Data.Lambda</hask> patterns emerged while working on [[DeepArrow]] and [[Eros]]. <hask>Data.Zip</hask> generalizes <hask>zip</hask> and <hask>unzip</hask> from <hask>[]</hask> to other functors. It also provides variants of type <hask>f a > f (a,b)</hask> and <hask>f a > f (a,b)</hask>. <hask>Data.Lambda</hask> is similar with classes for lambdalike constructions. 

+  
+  For example uses of <hask>Pair</hask> and <hask>Lambda</hask>, see [[TV]] and [[Eros]]. 

+  
+  === References === 

+  
+  Monads with references. Direct ripoff from [http://citeseer.ist.psu.edu/473734.html Global Variables in Haskell]. 

+  
+  === Titling === 

+  
+  For giving titles to things. I know it sounds kind of random. More useful than I first thought. Used in [[Phooey]], [[TV]], and [[Eros]]. 

+  
+  === Partial values === 

+  
+  A monoid of partial values. See the [http://conal.net/blog/posts/atypeforpartialvalues/ teaser] and [http://conal.net/blog/posts/implementingatypeforpartialvalues/ solution] blog 

+  posts. 

+  
+  === Contextdependent monoids === 

−  == Datadriven computation == 
+  Bit of an oddball also. <hask>Data.CxMonoid</hask> defines a sort of metamonoid, that can be supplied dynamically with choices of <hask>mempty</hask> and <hask>mappend</hask>. Used in [[Phooey]] (starting with version 1.3) so that layout could be a monoid but still vary in style. 
Latest revision as of 17:48, 9 January 2011
Contents 
[edit] 1 Abstract
TypeCompose provides some classes & instances for forms of type composition, as well as some modules that haven't found another home.
Besides this wiki page, here are more ways to find out about TypeCompose:
 Visit the Hackage page for library documentation and to download & install.
 Or install with cabal install TypeCompose.
 Get the code repository: darcs get http://code.haskell.org/~conal/code/TypeCompose.
[edit] 2 Type composition
TheControl.Compose
 Various type compositions (unary/unary, binary/unary, etc). Most are from Applicative Programming with Effects. In particular, composes functors in to functors and applicative functors (AFs) into AFs. (In contrast, monads do not in general compose.) Composition makes AFbased programming simple and elegant, partly because we don't need an AF counterpart to monad transformers.g `O` f
 Cofunctors (contravariant functors). Great for "consumer" types, just as functors suit "producer" (container) types. There are several composition options.
 Type argument flip. Handy for cofunctors: use , forFlip (>) o.(> o)
 Constructor in pairs: .(f a, g a)
 Constructor in arrows/functions: .f a ~> g a
[edit] 3 Other features
[edit] 3.1 Composable bijections
Given all the type constructors and compositions of them, I found myself writing some pretty awkward code to wrap & unwrap through multiple layers. Composable bijections help a lot.
TheData.Bijection
[edit] 3.2 Pair & functionlike types
TheData.Zip
Data.Lambda
Data.Zip
zip
unzip
[]
f a > f (a,b)
f a > f (a,b)
Data.Lambda
Pair
Lambda
[edit] 3.3 References
Monads with references. Direct ripoff from Global Variables in Haskell.
[edit] 3.4 Titling
For giving titles to things. I know it sounds kind of random. More useful than I first thought. Used in Phooey, TV, and Eros.
[edit] 3.5 Partial values
A monoid of partial values. See the teaser and solution blog posts.
[edit] 3.6 Contextdependent monoids
Bit of an oddball also.Data.CxMonoid
mempty
mappend