Homework/KarelSyntax.hs

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2019-02-25 01:05:39 -08:00
-- | This module defines the syntax of the Karel language.
module KarelSyntax where
-- | A Karel program is a list of macro definitions and a statement to
-- use as the body of the "main" function.
type Prog = (Defs,Stmt)
-- | A macro name.
type Macro = String
-- | A list of macro definitions.
type Defs = [(Macro,Stmt)]
-- | Cardinal directions.
data Card = North | South | East | West deriving (Eq,Show)
-- | Directions relative to the current facing.
data Dir = Front | Back | Right | Left deriving (Eq,Show)
-- | Environment queries.
data Test = Not Test -- boolean negation
| Facing Card -- am I facing the given cardinal direction?
| Clear Dir -- can I move in the given relative direction?
| Beeper -- is there a beeper here?
| Empty -- is my beeper bag empty?
deriving (Eq,Show)
-- | Statements.
data Stmt = Shutdown -- end the program
| Move -- move forward
| PickBeeper -- take a beeper
| PutBeeper -- leave a beeper
| Turn Dir -- rotate in place
| Call Macro -- invoke a macro
| Iterate Int Stmt -- fixed repetition loop
| If Test Stmt Stmt -- conditional branch
| While Test Stmt -- conditional loop
| Block [Stmt] -- statement block
deriving (Eq,Show)