Update screenshot to animated GIF (#139)

Author: jaspervdj

README.md

@@ -24,7 +24,7 @@ Features:
 - Supports [evaluating code snippets and showing the result](#evaluating-code).
 - Written in [Haskell].
 
-![screenshot](extra/screenshot.png?raw=true)
+![screenshot](extra/demo.gif?raw=true)
 
 [Kate]: https://kate-editor.org/
 [Haskell]: http://haskell.org/

extra/demo.gif

@@ -0,0 +1,141 @@
+---
+title: 'Logic Programming in Haskell'
+author: 'Jasper Van der Jeugt'
+patat:
+  incrementalLists: true
+  wrap: true
+  margins:
+    left: 1
+    right: 1
+  eval:
+    ghci:
+      command: 'tr -d "\n" | ghci | tail -n2 | head -n1'
+...
+
+# Filler
+
+## Filler
+
+## Filler
+
+## Filler
+
+## Filler
+
+# List Comprehensions
+
+## Introduction
+
+If we want to keep things simple, **list comprehensions** can be a powerful
+tool.
+
+~~~~~{.haskell}
+evens = [x | x <- [1..10], x `mod` 2 == 0]
+~~~~~
+
+Statements in list comprehensions are usually either:
+
+ -  _Pattern matches_ using `<-`
+ -  Expressions of type `Bool`
+
+. . .
+
+You can also `let` to introduce new bindings, but this is less common.
+
+## Laziness
+
+Due to Haskell's _laziness_, we don't traverse the whole search space.
+Searching for _triangular numbers_:
+
+~~~~~{.haskell .ghci}
+take 3 $
+    [ (a, b, c)
+    | c <- [1 .. 100000]
+    , b <- [1 .. c], a <- [1 .. b]
+    , a * a + b * b == c * c
+    ]
+~~~~~
+
+## Laziness
+
+Yo!
+
+# Filler
+
+## Filler
+
+Filler
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+## Filler
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+Filler
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+## Filler
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+Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler
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+## Filler

extra/demo.md

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+set -o nounset -o errexit -o pipefail
+
+mkdir -p cropped
+rm -f cropped/*
+for i in inputs/*; do
+    convert \
+        -alpha remove \
+        -crop '1280x1000+122+138' "$i" "cropped/$(basename "$i")"
+done
+
+rm -f patat.gif
+convert \
+    -repage '0x0' \
+    -layers coalesce \
+    -layers optimize-plus \
+    +repage \
+    -delay 150x100 \
+    -loop 0 \
+    cropped/*.png patat.gif