Work for CS-381, Programming Language Fundamentals
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-- | This module defines the syntax of MiniMiniLogo. It also provides
-- functions to generate programs that draw some basic shapes.
--
-- NOTE: You should not change the definitions in this file!
--
module MiniMiniLogo where
--
-- * Syntax
--
-- | A program is a sequence of commands.
type Prog = [Cmd]
-- | The mode of the pen.
data Mode = Down | Up
deriving (Eq,Show)
-- | Abstract syntax of commands.
data Cmd = Pen Mode
| Move Int Int
deriving (Eq,Show)
-- | Generate a MiniMiniLogo program that draws a 2x2 box starting from the
-- specified point. Conceptually, this program looks like the following, but
-- the additions are carried out in Haskell rather than in MiniMiniLogo.
--
-- pen up; move (x,y);
-- pen down; move (x+2,y); move (x+2,y+2);
-- move (x,y+2); move (x,y);
--
-- >>> box 7 3
-- [Pen Up,Move 7 3,Pen Down,Move 9 3,Move 9 5,Move 7 5,Move 7 3]
--
box :: Int -> Int -> Prog
box x y = [Pen Up, Move x y, Pen Down,
Move (x+2) y, Move (x+2) (y+2), Move x (y+2), Move x y]
-- | Generate an 'X' from (x,y) to (x+w,y+h).
--
-- >>> nix 10 10 5 7
-- [Pen Up,Move 10 10,Pen Down,Move 15 17,Pen Up,Move 10 17,Pen Down,Move 15 10]
--
nix :: Int -> Int -> Int -> Int -> Prog
nix x y w h = [Pen Up, Move x y, Pen Down, Move (x+w) (y+h),
Pen Up, Move x (y+h), Pen Down, Move (x+w) y]
-- | Generate a MiniMiniLogo program that draws n steps starting from
-- point (x,y).
--
-- >>> steps 3 2 4
-- [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]
--
steps :: Int -> Int -> Int -> Prog
steps n x y = [Pen Up, Move x y, Pen Down] ++ step n
where
step 0 = []
step n = step (n-1) ++ [Move (x+n-1) (y+n), Move (x+n) (y+n)]
-- | Draw an example picture. The expected output is given on the HW4
-- description page.
demo :: Prog
demo = box 7 3 ++ nix 6 6 4 3 ++ steps 3 2 4