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68 lines (47 loc) · 1.56 KB
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-------------------------------------------------------------------------
--
-- Haskell: The Craft of Functional Programming
-- Simon Thompson
-- (c) Addison-Wesley, 1999.
--
-- Chapter 1
--
-- The Pictures example code is given in the file Pitures.lhs.
-- This file can be used by importing it; more details are given in
-- Chapter 2.
--
-------------------------------------------------------------------------
module Chapter1 where
import Pictures hiding (rotate)
-- A first definition, of the integer value, size.
size :: Int
size = 12+13
-- Some definitions using Pictures.
-- Inverting the colour of the horse picture, ...
blackHorse :: Picture
blackHorse = invertColour horse
-- ... rotating the horse picture, ...
rotateHorse :: Picture
rotateHorse = flipH (flipV horse)
-- Some function definitions.
-- To square an integer, ...
square :: Int -> Int
square n = n*n
-- ... to double an integer, and ...
double :: Int -> Int
double n = 2*n
-- ... to rotate a picture we can perform the two reflections,
-- and so we define
rotate :: Picture -> Picture
rotate pic = flipH (flipV pic)
-- A different definition of rotateHorse can use rotate
rotateHorse1 :: Picture
rotateHorse1 = rotate horse
-- where the new definition is of a different name: you can't change a definition
-- in a script.
-- Defining rotate a different way, as a composition of functions; see the
-- diagram in the book for a picture of what's going on.
rotate1 :: Picture -> Picture
rotate1 = flipH . flipV
-- The definitions of the functions modelling pictures are in the file
-- Pictures.lhs.