{-# LANGUAGE GADTs, Rank2Types, CPP #-} -- Module : FRP.Yampa.Scan -- Copyright : (c) Antony Courtney and Henrik Nilsson, Yale University, 2003 -- License : BSD-style (see the LICENSE file in the distribution) -- -- Maintainer : ivan.perez@keera.co.uk -- Stability : provisional -- Portability : non-portable (GHC extensions) -- | Simple, stateful signal processing. -- -- Scanning implements elementary, step-based accumulating over signal -- functions by means of an auxiliary function applied to each input and to an -- accumulator. For comparison with other FRP libraries and with stream -- processing abstractions, think of fold. module FRP.Yampa.Scan ( sscan, -- :: (b -> a -> b) -> b -> SF a b sscanPrim, -- :: (c -> a -> Maybe (c, b)) -> c -> b -> SF a b ) where import FRP.Yampa.InternalCore (SF(..), sfSScan) -- ** Simple, stateful signal processing -- | Applies a function point-wise, using the last output as next input. This -- creates a well-formed loop based on a pure, auxiliary function. -- New sscan primitive. It should be possible to define lots of functions -- in terms of this one. Eventually a new constructor will be introduced if -- this works out. sscan :: (b -> a -> b) -> b -> SF a b sscan f b_init = sscanPrim f' b_init b_init where f' b a = let b' = f b a in Just (b', b') -- | Generic version of 'sscan', in which the auxiliary function produces -- an internal accumulator and an "held" output. -- -- Applies a function point-wise, using the last known 'Just' output to form -- the output, and next input accumulator. If the output is 'Nothing', the last -- known accumulators are used. This creates a well-formed loop based on a -- pure, auxiliary function. sscanPrim :: (c -> a -> Maybe (c, b)) -> c -> b -> SF a b sscanPrim f c_init b_init = SF {sfTF = tf0} where tf0 a0 = case f c_init a0 of Nothing -> (sfSScan f c_init b_init, b_init) Just (c', b') -> (sfSScan f c' b', b') -- Vim modeline -- vim:set tabstop=8 expandtab: