64 lines
1.9 KiB
Haskell
64 lines
1.9 KiB
Haskell
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-- | This module defines the syntax of MiniMiniLogo. It also provides
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-- functions to generate programs that draw some basic shapes.
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--
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-- NOTE: You should not change the definitions in this file!
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--
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module MiniMiniLogo where
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--
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-- * Syntax
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--
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-- | A program is a sequence of commands.
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type Prog = [Cmd]
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-- | The mode of the pen.
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data Mode = Down | Up
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deriving (Eq,Show)
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-- | Abstract syntax of commands.
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data Cmd = Pen Mode
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| Move Int Int
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deriving (Eq,Show)
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-- | Generate a MiniMiniLogo program that draws a 2x2 box starting from the
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-- specified point. Conceptually, this program looks like the following, but
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-- the additions are carried out in Haskell rather than in MiniMiniLogo.
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--
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-- pen up; move (x,y);
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-- pen down; move (x+2,y); move (x+2,y+2);
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-- move (x,y+2); move (x,y);
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--
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-- >>> box 7 3
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-- [Pen Up,Move 7 3,Pen Down,Move 9 3,Move 9 5,Move 7 5,Move 7 3]
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--
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box :: Int -> Int -> Prog
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box x y = [Pen Up, Move x y, Pen Down,
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Move (x+2) y, Move (x+2) (y+2), Move x (y+2), Move x y]
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-- | Generate an 'X' from (x,y) to (x+w,y+h).
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--
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-- >>> nix 10 10 5 7
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-- [Pen Up,Move 10 10,Pen Down,Move 15 17,Pen Up,Move 10 17,Pen Down,Move 15 10]
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--
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nix :: Int -> Int -> Int -> Int -> Prog
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nix x y w h = [Pen Up, Move x y, Pen Down, Move (x+w) (y+h),
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Pen Up, Move x (y+h), Pen Down, Move (x+w) y]
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-- | Generate a MiniMiniLogo program that draws n steps starting from
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-- point (x,y).
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--
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-- >>> steps 3 2 4
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-- [Pen Up,Move 2 4,Pen Down,Move 2 5,Move 3 5,Move 3 6,Move 4 6,Move 4 7,Move 5 7]
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--
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steps :: Int -> Int -> Int -> Prog
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steps n x y = [Pen Up, Move x y, Pen Down] ++ step n
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where
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step 0 = []
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step n = step (n-1) ++ [Move (x+n-1) (y+n), Move (x+n) (y+n)]
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-- | Draw an example picture. The expected output is given on the HW4
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-- description page.
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demo :: Prog
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demo = box 7 3 ++ nix 6 6 4 3 ++ steps 3 2 4
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