Graphics.WorldTurtle

Graphics.WorldTurtle is a module for writing and rendering turtle graphics in Haskell.

Take a look at the examples on Github!

Running the turtle

It is easy to create and animate your turtle. You just pass your commands to runTurtle like so:

     import Control.Monad (replicateM_)
     import Graphics.WorldTurtle

     myCommand :: TurtleCommand ()
     myCommand = do 
       t <- makeTurtle
       replicateM_ 4 $ forward 90 t >> right 90 t

     main :: IO ()
     main = runTurtle myCommand

Which will produce this animation

data TurtleCommand a

A TurtleCommand represents an instruction to execute. It could be as simple as "draw a line" or more complicated like "draw 300 circles."

TurtleCommands can be executed in order by combining them using the monadic operator (>>).

Here is an example of how to write a function that when given a size and a turtle, will return a new TurtleCommand which will draw a square with a length and breadth of size using turtle.

     drawSquare :: Float -> Turtle -> TurtleCommand ()
     drawSquare size t = replicateM_ 4 $ forward size t >> right 90 t
  

This draws a square by doing the following in order:

(1/4)

• Move forward by size amount.
• Turn right by 90 degrees

(2/4)

• Move forward by size amount.
• Turn right by 90 degrees

(3/4)

• Move forward by size amount.
• Turn right by 90 degrees

(4/4)

• Move forward by size amount.
• Turn right by 90 degrees

Instances

Monad TurtleCommand

Defined in Graphics.WorldTurtle.Internal.Commands

Methods

(>>=) :: TurtleCommand a -> (a -> TurtleCommand b) -> TurtleCommand b

(>>) :: TurtleCommand a -> TurtleCommand b -> TurtleCommand b

return :: a -> TurtleCommand a

Functor TurtleCommand

Defined in Graphics.WorldTurtle.Internal.Commands

Methods

fmap :: (a -> b) -> TurtleCommand a -> TurtleCommand b

(<$) :: a -> TurtleCommand b -> TurtleCommand a

MonadFail TurtleCommand

Defined in Graphics.WorldTurtle.Internal.Commands

Methods

fail :: String -> TurtleCommand a

Applicative TurtleCommand

Defined in Graphics.WorldTurtle.Internal.Commands

Methods

pure :: a -> TurtleCommand a

(<*>) :: TurtleCommand (a -> b) -> TurtleCommand a -> TurtleCommand b

liftA2 :: (a -> b -> c) -> TurtleCommand a -> TurtleCommand b -> TurtleCommand c

(*>) :: TurtleCommand a -> TurtleCommand b -> TurtleCommand b

(<*) :: TurtleCommand a -> TurtleCommand b -> TurtleCommand a

Alternative TurtleCommand

Defined in Graphics.WorldTurtle.Internal.Commands

Methods

empty :: TurtleCommand a

(<|>) :: TurtleCommand a -> TurtleCommand a -> TurtleCommand a

some :: TurtleCommand a -> TurtleCommand [a]

many :: TurtleCommand a -> TurtleCommand [a]

MonadPlus TurtleCommand

Defined in Graphics.WorldTurtle.Internal.Commands

Methods

mzero :: TurtleCommand a

mplus :: TurtleCommand a -> TurtleCommand a -> TurtleCommand a

Semigroup a => Semigroup (TurtleCommand a)

Defined in Graphics.WorldTurtle.Internal.Commands

Methods

(<>) :: TurtleCommand a -> TurtleCommand a -> TurtleCommand a

sconcat :: NonEmpty (TurtleCommand a) -> TurtleCommand a

stimes :: Integral b => b -> TurtleCommand a -> TurtleCommand a

runTurtle

Arguments

:: TurtleCommand ()

Command sequence to execute

-> IO ()

runTurtle takes a TurtleCommand and produces the animation in a new window!

The simplest way to run runTurtle is to execute it directly from your main function like so:

        main :: IO ()
        main = runTurtle yourOwnCoolCommand
    

While running, you can interact with the window in the following way:

Action	Interaction
Pan the viewport.	Click and drag
Zoom in/out.	Mousewheel up/down
Reset the viewport to initial position.	Spacebar
Reset the animation.	R key
Pause the animation.	P key
Quit	Escape key

Parallel animation

We already know that TurtleCommands can be combined with (>>), but the alternative operation (<|>) can alo be used to combine two TurtleCommands. This has a special meaning: do both animations at the same time!

Note that the result of a <|> b is:

>>> a <|> b
a

when a is not mzero.

(<|>) :: Alternative f => f a -> f a -> f a infixl 3

An associative binary operation

Further documentation

module Graphics.WorldTurtle.Commands

module Graphics.WorldTurtle.Shapes

module Graphics.WorldTurtle.Color