Free ToyRobot (with mtl)

Implementation of a ToyRobot using Free.

Robot DSL

Instruction	Arguments	API	Description
Place	(Integer, Integer)	place (x,y)	Place a robot at (x,y)
Report	-	report	Report current state (position atm)
Move	-	move	Move the robot in the current direction
TurnLeft	-	turnLeft	Turn left
TurnRight	-	turnRight	Turn right
Done	-	done	Terminate evaluation

Note: CLI is coupled with RobotDSL atm (Steer action; not listed above). Will try using Coproducts to decouple.

Example usage

In stack repl:

Inline evaluation

Use play to run a sequence in a monad stack with super powers!

λ> play $ <sequence>

Example:

λ> import Control.Monad -- to use replicateM_
λ> play $ place (0,0) >> replicateM_ 2 move >> turnRight >> move >> report
World {_robot = Robot {_location = V2 1 2, _direction = East, _name = "Wall-e"}}
((Right (),[]),World {_robot = Robot {_location = V2 1 2, _direction = East, _name = "Wall-e"}})

Repl

λ> play repl
robot#repl>report
World {_robot = Robot {_location = V2 0 0, _direction = North, _name = "Wall-e"}}
robot#repl>

Building AST(s)

Note: printingInterpreter does not exist - write it yourself!

λ> printingInterpreter $ place (1,3) >> report >> place (9,5) >> report >> done
Free (Place (1,3) (Free (Report (Free (Place (9,5) (Free (Report (Free Done))))))))

You can now use the generated AST however you want in your interpreter!

Example sequences:

done
report >> done
place (1,1) >> report >> place (2,6) >> done >> report
report >> place (20, 5) >> report >> done
turnRight >> turnLeft >> replicateM_ 2 turnRight
replicateM_ 5 turnLeft
place (0,0) >> replicateM_ 2 move >> turnRight >> move >> report

Monad Stack Example (with Super Powers!)

type EvalStack s m =
  (Show s, MonadIO m, MonadState s m, MonadError String m, MonadReader Env m, MonadWriter [Name] m)