Editing Tangible Value (section)

== Transmission-specific interfaces ==

While some interfaces can be implemented for different means of transmission, others are more specialized.

=== GUIs ===

Here are inputs for our shopping example above that specifically work with [[Phooey]]'s UI applicative functor.
<haskell>
applesU, bananasU :: Input UI Int
applesU  = iTitle "apples"  (islider 3 (0,10))
bananasU = iTitle "bananas" (islider 7 (0,10))

shoppingUO :: Output UI (Int -> Int -> Int)
shoppingUO = oTitle "shopping list" $ oLambda applesU (oLambda bananasU total)
</haskell>

We can then make curried and uncurried TVs:
<blockquote>
{| class="wikitable"
! code !! runUI rendering 
|-
| style="padding:20px;" align=right| <hask>tv shoppingUO (+)</hask>
| style="padding:20px;" align="center" | [[Image:shoppingU.png]]
|-
| style="padding:20px;" align=right | <hask>uncurryA $$ tv shoppingUO (+)</hask>
| style="padding:20px;" align="center" | [[Image:shoppingPrU.png]]
|}
</blockquote>

'''Note''': We could define other type classes, besides <hask>CommonInsOuts</hask>.  For instance,  <hask>islider</hask> could be made a method of a <hask>GuiArrow</hask> class, allowing it to be rendered in different ways with different GUI toolkits or even using HTML and Javascript.

=== IO ===

We can use <hask>IO</hask> operations in TV interfaces.  The corresponding sink is <hask>OI</hask>, defined in [[TypeCompose]].  TV provides a few functions in its [http://hackage.haskell.org/package/TV/latest/doc/html/Interface-TV-IO.html <hask>IO</hask> module], including a close counterpart to the standard <hask>interact</hask> function.
<haskell>
interactOut :: Output IO OI (String -> String)
interactOut = oLambda contentsIn stringOut
</haskell>

Assuming we have a file <tt>"test.txt"</tt> containing some lines of text, we can use it to test string transformations.
<haskell>
testO :: Output IO OI (String -> String)
testO = oLambda (fileIn "test.txt") defaultOut
</haskell>

First, let's define higher-order functions that apply another function to the lines or on the words of a string.
<haskell>
onLines, onWords :: ([String] -> [String]) -> (String -> String)
onLines f = unlines . f . lines
onWords f = unwords . f . words
</haskell>
Next, specializations that operate on ''each'' line or word:
<haskell>
perLine,perWord :: (String -> String) -> (String -> String)
perLine f = onLines (map f)
perWord f = onWords (map f)
</haskell>

Some examples:

<blockquote>
{| class="wikitable"
! string function <hask>f</hask> !! <hask>runIO (tv test0 f)</hask>
|-
| style="padding:20px;" align=right| <hask>id</hask>
| style="padding:20px;" align="center" |
 To see a World in a Grain of Sand
 And a Heaven in a Wild Flower, 
 Hold Infinity in the palm of your hand
 And Eternity in an hour.
     - William Blake
|-
| style="padding:20px;" align=right| <hask>reverse</hask>
| style="padding:20px;" align="center" |

 ekalB mailliW -    
 .ruoh na ni ytinretE dnA
 dnah ruoy fo mlap eht ni ytinifnI dloH
  ,rewolF dliW a ni nevaeH a dnA
 dnaS fo niarG a ni dlroW a ees oT
|-
| style="padding:20px;" align=right| <hask>onLines reverse</hask>
| style="padding:20px;" align="center" |
     - William Blake
 And Eternity in an hour.
 Hold Infinity in the palm of your hand
 And a Heaven in a Wild Flower, 
 To see a World in a Grain of Sand
|-
| style="padding:20px;" align=right| <hask>perLine reverse</hask>
| style="padding:20px;" align="center" |
 dnaS fo niarG a ni dlroW a ees oT
  ,rewolF dliW a ni nevaeH a dnA
 dnah ruoy fo mlap eht ni ytinifnI dloH
 .ruoh na ni ytinretE dnA
 ekalB mailliW -    
|-
| style="padding:20px;" align=right| <hask>perLine (perWord reverse)</hask>
| style="padding:20px;" align="center" |
 oT ees a dlroW ni a niarG fo dnaS
 dnA a nevaeH ni a dliW ,rewolF
 dloH ytinifnI ni eht mlap fo ruoy dnah
 dnA ytinretE ni na .ruoh
 - mailliW ekalB
|}
</blockquote>

There are more examples [http://code.haskell.org/~conal/code/TV/src/Examples.hs in the TV repository] and in the [http://code.haskell.org/~conal/code/GuiTV/src/Examples.hs in the GuiTV repository].  See also "[http://journal.conal.net/#%5B%5Bseparating%20IO%20from%20logic%20--%20example%5D%5D separating IO from logic -- example]".