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Running primitive signal functions in Yampa

To test signal functions in Yampa, use the embed function. Enter the following commands in the Haskell command-line to show the header definition:

> :type FRP.Yampa.embed

FRP.Yampa.embed :: FRP.Yampa.SF a b -> (a, [(FRP.Yampa.DTime, Maybe a)]) -> [b]

So the parameters are:

  1. the signal function to run
  2. a tuple of…
    1. the first input value at time=0
    2. and a list of…
      1. (time, Nothing|Just nextValue)

and return a list of values produced by the signal function.

Primitive signal functions include: time, identity and constant

main :: IO ()
main = do
    putStrLn $ show $ embed time (Nothing, [(1.0, Nothing), (0.2, Nothing), (0.03, Nothing)])
    putStrLn $ show $ embed time (123, [(1.0, Just 234), (0.2, Just 345), (0.03, Just 456)])
    -- [0.0,1.0,1.2,1.23]
    -- [0.0,1.0,1.2,1.23]

    putStrLn $ show $ embed identity (123, [(1.0, Just 234), (0.2, Just 345), (0.03, Just 456)])
    putStrLn $ show $ embed identity (537, [(1.0, Nothing), (0.2, Nothing), (0.03, Just 123)])
    -- [123,234,345,456]
    -- [537,537,537,537]

    putStrLn $ show $ embed (constant 537) (Nothing, [(1.0, Nothing), (0.2, Nothing), (0.03, Nothing)])
    putStrLn $ show $ embed (constant 537) (123, [(1.0, Just 234), (0.2, Just 345), (0.03, Just 456)])
    -- putStrLn $ show (embed constant (123, [(1.0, Just 234), (0.2, Just 345), (0.03, Just 456)])) -- ERROR
    -- [537,537,537,537]
    -- [537,537,537,537]

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8 Responses

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    Just wondering… Why’s that a `Maybe a` and not just an `a`?

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Continuing the Discussion

  1. Learning Yampa and Functional Reactive Programming | Lambdor Devblog linked to this post on 2011-04-30

    [...] Running primitive signal functions in Yampa Yampa/SDL program stub [...]

  2. Haskell Yampa « Code Contemplation linked to this post on 2012-07-28

    [...] suggested here primitive signal functions can be tested using the embed function. For example: putStrLn $ show $ [...]



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