Embedded Languages for Graphical Programming

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Embedded Languages for Graphical Programming

• Koen Lindström Claessen
• Chalmers University
• Gothenburg, Sweden

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Topics Today

• Fudgets Embedded language for GUI programming
• Pan Embedded language for describing pictures
  and animations
• Give you a flavor

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Embedded Language

• Library
• Compositional
• (Abstract) type -- modelling
• Creation functions
• Combinators
• Not always a monad ?

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Fudgets

• First real GUI library for Haskell
• Developed in 1990s (pre-monad era)
• Magnus Carlsson
• Thomas Hallgren
• Still active

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The Fudget
Messages of type a, b functional behavior
a
b
Also a graphical representation
type F a b
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Example A Button
()
()
Hello
button String -gt F () ()
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Example An Entry
String
String
12.0
entry F String String
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Fudget Composition
a
b
c
(gtlt) F a b -gt F b c -gt F a c
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Fudget Composition
a
b
c
a
(gtlt) F a b -gt F a b -gt F a b
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Example An Abstract Fudget
a
b
mapF (a -gt b) -gt F a b
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Example Spinner
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Example
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Example
spin F a (Int -gt Int) spin nil gtlt (
button gtlt mapF (\_ -gt succ) gtlt button
- gtlt mapF (\_ -gt pred) ) spinner
F Int Int spinner loop ( (mapF const gtlt
spin) gtlt count gtlt entryInt
)
nil ignores input
loop ties the knot
count does the counting
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Fudgets -- Summary

• Pick the thing to model
• A Fudget
• Widget Functionality
• Pick a type
• Design combinators

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Implementing Fudgets

• Shallow embedding?
• Deep embedding?

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Pan Functional Images
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Embedded Language for Images
type Point (Double,Double) type Image a Point
-gt a
type Region Image Bool
type Color ... type Picture Image Color
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Examples
vstrip Region vstrip (x,y) abs x lt 0.5
checker Region checker (x,y) even (floor
x floor y)
altRings Region altRings p even (distO
p) distO (x,y) sqrt (xx yy)
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Liftings
lift1 (a -gt b) -gt Image a -gt Image b lift2
(a -gt b -gt c) -gt Image a -gt Image b -gt Image c ...
over Picture -gt Picture -gt Picture over
lift2 overColor
cond Region -gt Picture -gt Picture -gt
Picture cond lift3 (\b x y -gt if b then x else
y)
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Swirling
type Filter a Image a -gt Image a
swirl Double -gt Filter a swirl r im im
. (\p -gt rotate (distO p 2 pi / -r) p
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Image Viewer

• There is an image viewer
• You can set parameters
• Sliders
• Time

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Implementation?

• How to implement this efficiently?
• Shallow implementation?
• Deep implementation?

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What we saw

• Embedded Languages
• Graphics
• Compositional
• Shallow embedding for understanding
• Deep embedding can be compiled
• Not everything is a monad

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Further Reading -- Take a look at

• Fran Functional Reactive Animations
• Yampa Fran (version 2)