{-# LANGUAGE GADTs, Rank2Types, CPP #-}
-----------------------------------------------------------------------------------------
-- |
-- Module : FRP.Yampa.Switches
-- 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)
--
-- Switches allow you to change the signal function being applied.
--
-- The basic idea of switching is fromed by combining a subordinate signal function
-- and a signal function continuation parameterised over some initial data.
--
-- For example, the most basic switch has the following signature:
--
-- @switch :: SF a (b, Event c) -> (c -> SF a b) -> SF a b@
--
-- which indicates that it has two parameters: a signal function
-- that produces an output and indicates, with an event, when it is time to
-- switch, and a signal function that starts with the residual data left by the
-- first SF in the event and continues onwards.
--
-- Switching occurs, at most, once. If you want something to switch repeatedly,
-- in general, you need to loop, or to switch onto the same signal function
-- again. However, some switches, explained below, are immediate (meaning that
-- the second SF is started at the time of switching). If you use the same SF
-- that originally provoked the switch, you are very likely to fall into an
-- infinite loop. In those cases, the use of 'dSwitch' or '-->' may help.
--
-- Switches vary depending on a number of criterions:
--
-- - /Decoupled/ vs normal switching /(d)/: when an SF is being applied and a
-- different SF needs to be applied next, one question is which one is used
-- for the time in which the switching takes place. In decoupled switching, the
-- old SF is used for the time of switching, and the one SF is only used after
-- that. In normal or instantaneous or coupled switching, the old SF is
-- discarded immediately and a new SF is used for the output already from that
-- point in time.
--
-- - How the switching event is provided /( \/r\/k)/: normally, an 'Event' is
-- used to indicate that a switching must take place. This event can be part of
-- the argument SF (e.g., 'switch'), it can be part of the input (e.g.,
-- 'rSwitch'), or it can be determined by a second argument SF (e.g,
-- 'kSwitch').
--
-- - How many SFs are being handled /( \/p\/par)/: some combinators deal with
-- only one SF, others handle collections, either in the form of a
--'Functor' or a list ('[]').
--
-- - How the input is router /(B\/Z\/ )/: when multiple SFs are being combined,
-- a decision needs to be made about how the input is passed to the internal
-- SFs. In some cases, broadcasting is used to pass the same input to all
-- internal SFs. In others, the input is itself a collection, and each element
-- is passed to one internal SF (i.e., /zipping/). In others, an auxiliary
-- function is used to decide how to route specific inputs to specific SFs in
-- the collection.
--
-- These gives a number of different combinations, some of which make no sense,
-- and also helps determine the expected behaviour of a combinator by looking
-- at its name. For example, 'drpSwitchB' is the decoupled (/d/), recurrent
-- (/r/), parallel (/p/) switch with broadcasting (/B/).
module FRP.Yampa.Switches (
-- * Basic switching
switch, dSwitch, -- :: SF a (b, Event c) -> (c -> SF a b) -> SF a b
rSwitch, drSwitch, -- :: SF a b -> SF (a,Event (SF a b)) b
kSwitch, dkSwitch, -- :: SF a b
-- -> SF (a,b) (Event c)
-- -> (SF a b -> c -> SF a b)
-- -> SF a b
-- * Parallel composition\/switching (collections)
-- ** With broadcasting
parB, -- :: Functor col => col (SF a b) -> SF a (col b)
pSwitchB,dpSwitchB, -- :: Functor col =>
-- col (SF a b)
-- -> SF (a, col b) (Event c)
-- -> (col (SF a b) -> c -> SF a (col b))
-- -> SF a (col b)
rpSwitchB,drpSwitchB,-- :: Functor col =>
-- col (SF a b)
-- -> SF (a, Event (col (SF a b)->col (SF a b)))
-- (col b)
-- ** With helper routing function
par, -- Functor col =>
-- (forall sf . (a -> col sf -> col (b, sf)))
-- -> col (SF b c)
-- -> SF a (col c)
pSwitch, dpSwitch, -- pSwitch :: Functor col =>
-- (forall sf . (a -> col sf -> col (b, sf)))
-- -> col (SF b c)
-- -> SF (a, col c) (Event d)
-- -> (col (SF b c) -> d -> SF a (col c))
-- -> SF a (col c)
rpSwitch,drpSwitch, -- Functor col =>
-- (forall sf . (a -> col sf -> col (b, sf)))
-- -> col (SF b c)
-- -> SF (a, Event (col (SF b c) -> col (SF b c)))
-- (col c)
--
-- * Parallel composition\/switching (lists)
--
-- ** With "zip" routing
parZ, -- [SF a b] -> SF [a] [b]
pSwitchZ, -- [SF a b] -> SF ([a],[b]) (Event c)
-- -> ([SF a b] -> c -> SF [a] [b]) -> SF [a] [b]
dpSwitchZ, -- [SF a b] -> SF ([a],[b]) (Event c)
-- -> ([SF a b] -> c ->SF [a] [b]) -> SF [a] [b]
rpSwitchZ, -- [SF a b] -> SF ([a], Event ([SF a b]->[SF a b])) [b]
drpSwitchZ, -- [SF a b] -> SF ([a], Event ([SF a b]->[SF a b])) [b]
-- ** With replication
parC, -- SF a b -> SF [a] [b]
) where
import Control.Arrow
import FRP.Yampa.Diagnostics
import FRP.Yampa.InternalCore (SF(..), SF'(..), sfTF', sfConst, fdFun, FunDesc(..), sfArrG, DTime)
import FRP.Yampa.Basic
import FRP.Yampa.Event
------------------------------------------------------------------------------
-- Basic switches
------------------------------------------------------------------------------
-- !!! Interesting case. It seems we need scoped type variables
-- !!! to be able to write down the local type signatures.
-- !!! On the other hand, the scoped type variables seem to
-- !!! prohibit the kind of unification that is needed for GADTs???
-- !!! Maybe this could be made to wok if it actually WAS known
-- !!! that scoped type variables indeed corresponds to universally
-- !!! quantified variables? Or if one were to keep track of those
-- !!! scoped type variables that actually do?
-- !!!
-- !!! Find a simpler case to experiment further. For now, elim.
-- !!! the free variable.
{-
-- Basic switch.
switch :: SF a (b, Event c) -> (c -> SF a b) -> SF a b
switch (SF {sfTF = tf10} :: SF a (b, Event c)) (k :: c -> SF a b) = SF {sfTF = tf0}
where
tf0 a0 =
case tf10 a0 of
(sf1, (b0, NoEvent)) -> (switchAux sf1, b0)
(_, (_, Event c0)) -> sfTF (k c0) a0
-- It would be nice to optimize further here. E.g. if it would be
-- possible to observe the event source only.
switchAux :: SF' a (b, Event c) -> SF' a b
switchAux (SFId _) = switchAuxA1 id -- New
switchAux (SFConst _ (b, NoEvent)) = sfConst b
switchAux (SFArr _ f1) = switchAuxA1 f1
switchAux sf1 = SF' tf
where
tf dt a =
case (sfTF' sf1) dt a of
(sf1', (b, NoEvent)) -> (switchAux sf1', b)
(_, (_, Event c)) -> sfTF (k c) a
-- Could be optimized a little bit further by having a case for
-- identity, switchAuxI1
-- Note: While switch behaves as a stateless arrow at this point, that
-- could change after a switch. Hence, SF' overall.
switchAuxA1 :: (a -> (b, Event c)) -> SF' a b
switchAuxA1 f1 = sf
where
sf = SF' tf
tf _ a =
case f1 a of
(b, NoEvent) -> (sf, b)
(_, Event c) -> sfTF (k c) a
-}
-- | Basic switch.
--
-- By default, the first signal function is applied. Whenever the second value
-- in the pair actually is an event, the value carried by the event is used to
-- obtain a new signal function to be applied *at that time and at future
-- times*. Until that happens, the first value in the pair is produced in the
-- output signal.
--
-- Important note: at the time of switching, the second signal function is
-- applied immediately. If that second SF can also switch at time zero, then a
-- double (nested) switch might take place. If the second SF refers to the
-- first one, the switch might take place infinitely many times and never be
-- resolved.
--
-- Remember: The continuation is evaluated strictly at the time
-- of switching!
switch :: SF a (b, Event c) -> (c -> SF a b) -> SF a b
switch (SF {sfTF = tf10}) k = SF {sfTF = tf0}
where
tf0 a0 =
case tf10 a0 of
(sf1, (b0, NoEvent)) -> (switchAux sf1 k, b0)
(_, (_, Event c0)) -> sfTF (k c0) a0
-- It would be nice to optimize further here. E.g. if it would be
-- possible to observe the event source only.
switchAux :: SF' a (b, Event c) -> (c -> SF a b) -> SF' a b
switchAux (SFArr _ (FDC (b, NoEvent))) _ = sfConst b
switchAux (SFArr _ fd1) k = switchAuxA1 (fdFun fd1) k
switchAux sf1 k = SF' tf
{-
if sfIsInv sf1 then
switchInv sf1 k
else
SF' tf False
-}
where
tf dt a =
case (sfTF' sf1) dt a of
(sf1', (b, NoEvent)) -> (switchAux sf1' k, b)
(_, (_, Event c)) -> sfTF (k c) a
{-
-- Note: subordinate signal function being invariant does NOT
-- imply that the overall signal function is.
switchInv :: SF' a (b, Event c) -> (c -> SF a b) -> SF' a b
switchInv sf1 k = SF' tf False
where
tf dt a =
case (sfTF' sf1) dt a of
(sf1', (b, NoEvent)) -> (switchInv sf1' k, b)
(_, (_, Event c)) -> sfTF (k c) a
-}
-- !!! Could be optimized a little bit further by having a case for
-- !!! identity, switchAuxI1. But I'd expect identity is so unlikely
-- !!! that there is no point.
-- Note: While switch behaves as a stateless arrow at this point, that
-- could change after a switch. Hence, SF' overall.
switchAuxA1 :: (a -> (b, Event c)) -> (c -> SF a b) -> SF' a b
switchAuxA1 f1 k = sf
where
sf = SF' tf -- False
tf _ a =
case f1 a of
(b, NoEvent) -> (sf, b)
(_, Event c) -> sfTF (k c) a
-- | Switch with delayed observation.
--
-- By default, the first signal function is applied.
--
-- Whenever the second value in the pair actually is an event,
-- the value carried by the event is used to obtain a new signal
-- function to be applied *at future times*.
--
-- Until that happens, the first value in the pair is produced
-- in the output signal.
--
-- Important note: at the time of switching, the second
-- signal function is used immediately, but the current
-- input is fed by it (even though the actual output signal
-- value at time 0 is discarded).
--
-- If that second SF can also switch at time zero, then a
-- double (nested) -- switch might take place. If the second SF refers to the
-- first one, the switch might take place infinitely many times and never be
-- resolved.
--
-- Remember: The continuation is evaluated strictly at the time
-- of switching!
-- Alternative name: "decoupled switch"?
-- (The SFId optimization is highly unlikley to be of much use, but it
-- does raise an interesting typing issue.)
dSwitch :: SF a (b, Event c) -> (c -> SF a b) -> SF a b
dSwitch (SF {sfTF = tf10}) k = SF {sfTF = tf0}
where
tf0 a0 =
let (sf1, (b0, ec0)) = tf10 a0
in (case ec0 of
NoEvent -> dSwitchAux sf1 k
Event c0 -> fst (sfTF (k c0) a0),
b0)
-- It would be nice to optimize further here. E.g. if it would be
-- possible to observe the event source only.
dSwitchAux :: SF' a (b, Event c) -> (c -> SF a b) -> SF' a b
dSwitchAux (SFArr _ (FDC (b, NoEvent))) _ = sfConst b
dSwitchAux (SFArr _ fd1) k = dSwitchAuxA1 (fdFun fd1) k
dSwitchAux sf1 k = SF' tf
{-
if sfIsInv sf1 then
dSwitchInv sf1 k
else
SF' tf False
-}
where
tf dt a =
let (sf1', (b, ec)) = (sfTF' sf1) dt a
in (case ec of
NoEvent -> dSwitchAux sf1' k
Event c -> fst (sfTF (k c) a),
b)
{-
-- Note: that the subordinate signal function is invariant does NOT
-- imply that the overall signal function is.
dSwitchInv :: SF' a (b, Event c) -> (c -> SF a b) -> SF' a b
dSwitchInv sf1 k = SF' tf False
where
tf dt a =
let (sf1', (b, ec)) = (sfTF' sf1) dt a
in (case ec of
NoEvent -> dSwitchInv sf1' k
Event c -> fst (sfTF (k c) a),
b)
-}
-- !!! Could be optimized a little bit further by having a case for
-- !!! identity, switchAuxI1
-- Note: While dSwitch behaves as a stateless arrow at this point, that
-- could change after a switch. Hence, SF' overall.
dSwitchAuxA1 :: (a -> (b, Event c)) -> (c -> SF a b) -> SF' a b
dSwitchAuxA1 f1 k = sf
where
sf = SF' tf -- False
tf _ a =
let (b, ec) = f1 a
in (case ec of
NoEvent -> sf
Event c -> fst (sfTF (k c) a),
b)
-- | Recurring switch.
--
-- Uses the given SF until an event comes in the input, in which case the SF in
-- the event is turned on, until the next event comes in the input, and so on.
--
-- See for more
-- information on how this switch works.
-- !!! Suboptimal. Overall, the constructor is invarying since rSwitch is
-- !!! being invoked recursively on a switch. In fact, we don't even care
-- !!! whether the subordinate signal function is invarying or not.
-- !!! We could make use of a signal function transformer sfInv to
-- !!! mark the constructor as invarying. Would that make sense?
-- !!! The price would be an extra loop with case analysis.
-- !!! The potential gain is fewer case analyses in superior loops.
rSwitch :: SF a b -> SF (a, Event (SF a b)) b
rSwitch sf = switch (first sf) ((noEventSnd >=-) . rSwitch)
{-
-- Old version. New is more efficient. Which one is clearer?
rSwitch :: SF a b -> SF (a, Event (SF a b)) b
rSwitch sf = switch (first sf) rSwitch'
where
rSwitch' sf = switch (sf *** notYet) rSwitch'
-}
-- | Recurring switch with delayed observation.
--
-- Uses the given SF until an event comes in the input, in which case the SF in
-- the event is turned on, until the next event comes in the input, and so on.
--
-- Uses decoupled switch ('dSwitch').
--
-- See for more
-- information on how this switch works.
drSwitch :: SF a b -> SF (a, Event (SF a b)) b
drSwitch sf = dSwitch (first sf) ((noEventSnd >=-) . drSwitch)
{-
-- Old version. New is more efficient. Which one is clearer?
drSwitch :: SF a b -> SF (a, Event (SF a b)) b
drSwitch sf = dSwitch (first sf) drSwitch'
where
drSwitch' sf = dSwitch (sf *** notYet) drSwitch'
-}
-- | Call-with-current-continuation switch.
--
-- Applies the first SF until the input signal and the output signal, when
-- passed to the second SF, produce an event, in which case the original SF and
-- the event are used to build an new SF to switch into.
--
-- See for more
-- information on how this switch works.
-- !!! Has not been optimized properly.
-- !!! Nor has opts been tested!
-- !!! Don't forget Inv opts!
kSwitch :: SF a b -> SF (a,b) (Event c) -> (SF a b -> c -> SF a b) -> SF a b
kSwitch sf10@(SF {sfTF = tf10}) (SF {sfTF = tfe0}) k = SF {sfTF = tf0}
where
tf0 a0 =
let (sf1, b0) = tf10 a0
in
case tfe0 (a0, b0) of
(sfe, NoEvent) -> (kSwitchAux sf1 sfe, b0)
(_, Event c0) -> sfTF (k sf10 c0) a0
-- Same problem as above: must pass k explicitly???
-- kSwitchAux (SFId _) sfe = kSwitchAuxI1 sfe
kSwitchAux (SFArr _ (FDC b)) sfe = kSwitchAuxC1 b sfe
kSwitchAux (SFArr _ fd1) sfe = kSwitchAuxA1 (fdFun fd1) sfe
-- kSwitchAux (SFArrE _ f1) sfe = kSwitchAuxA1 f1 sfe
-- kSwitchAux (SFArrEE _ f1) sfe = kSwitchAuxA1 f1 sfe
kSwitchAux sf1 (SFArr _ (FDC NoEvent)) = sf1
kSwitchAux sf1 (SFArr _ fde) = kSwitchAuxAE sf1 (fdFun fde)
-- kSwitchAux sf1 (SFArrE _ fe) = kSwitchAuxAE sf1 fe
-- kSwitchAux sf1 (SFArrEE _ fe) = kSwitchAuxAE sf1 fe
kSwitchAux sf1 sfe = SF' tf -- False
where
tf dt a =
let (sf1', b) = (sfTF' sf1) dt a
in
case (sfTF' sfe) dt (a, b) of
(sfe', NoEvent) -> (kSwitchAux sf1' sfe', b)
(_, Event c) -> sfTF (k (freeze sf1 dt) c) a
{-
-- !!! Untested optimization!
kSwitchAuxI1 (SFConst _ NoEvent) = sfId
kSwitchAuxI1 (SFArr _ fe) = kSwitchAuxI1AE fe
kSwitchAuxI1 sfe = SF' tf
where
tf dt a =
case (sfTF' sfe) dt (a, a) of
(sfe', NoEvent) -> (kSwitchAuxI1 sfe', a)
(_, Event c) -> sfTF (k identity c) a
-}
-- !!! Untested optimization!
kSwitchAuxC1 b (SFArr _ (FDC NoEvent)) = sfConst b
kSwitchAuxC1 b (SFArr _ fde) = kSwitchAuxC1AE b (fdFun fde)
-- kSwitchAuxC1 b (SFArrE _ fe) = kSwitchAuxC1AE b fe
-- kSwitchAuxC1 b (SFArrEE _ fe) = kSwitchAuxC1AE b fe
kSwitchAuxC1 b sfe = SF' tf -- False
where
tf dt a =
case (sfTF' sfe) dt (a, b) of
(sfe', NoEvent) -> (kSwitchAuxC1 b sfe', b)
(_, Event c) -> sfTF (k (constant b) c) a
-- !!! Untested optimization!
kSwitchAuxA1 f1 (SFArr _ (FDC NoEvent)) = sfArrG f1
kSwitchAuxA1 f1 (SFArr _ fde) = kSwitchAuxA1AE f1 (fdFun fde)
-- kSwitchAuxA1 f1 (SFArrE _ fe) = kSwitchAuxA1AE f1 fe
-- kSwitchAuxA1 f1 (SFArrEE _ fe) = kSwitchAuxA1AE f1 fe
kSwitchAuxA1 f1 sfe = SF' tf -- False
where
tf dt a =
let b = f1 a
in
case (sfTF' sfe) dt (a, b) of
(sfe', NoEvent) -> (kSwitchAuxA1 f1 sfe', b)
(_, Event c) -> sfTF (k (arr f1) c) a
-- !!! Untested optimization!
-- kSwitchAuxAE (SFId _) fe = kSwitchAuxI1AE fe
kSwitchAuxAE (SFArr _ (FDC b)) fe = kSwitchAuxC1AE b fe
kSwitchAuxAE (SFArr _ fd1) fe = kSwitchAuxA1AE (fdFun fd1) fe
-- kSwitchAuxAE (SFArrE _ f1) fe = kSwitchAuxA1AE f1 fe
-- kSwitchAuxAE (SFArrEE _ f1) fe = kSwitchAuxA1AE f1 fe
kSwitchAuxAE sf1 fe = SF' tf -- False
where
tf dt a =
let (sf1', b) = (sfTF' sf1) dt a
in
case fe (a, b) of
NoEvent -> (kSwitchAuxAE sf1' fe, b)
Event c -> sfTF (k (freeze sf1 dt) c) a
{-
-- !!! Untested optimization!
kSwitchAuxI1AE fe = SF' tf -- False
where
tf dt a =
case fe (a, a) of
NoEvent -> (kSwitchAuxI1AE fe, a)
Event c -> sfTF (k identity c) a
-}
-- !!! Untested optimization!
kSwitchAuxC1AE b fe = SF' tf -- False
where
tf _ a =
case fe (a, b) of
NoEvent -> (kSwitchAuxC1AE b fe, b)
Event c -> sfTF (k (constant b) c) a
-- !!! Untested optimization!
kSwitchAuxA1AE f1 fe = SF' tf -- False
where
tf _ a =
let b = f1 a
in
case fe (a, b) of
NoEvent -> (kSwitchAuxA1AE f1 fe, b)
Event c -> sfTF (k (arr f1) c) a
-- | 'kSwitch' with delayed observation.
--
-- Applies the first SF until the input signal and the output signal, when
-- passed to the second SF, produce an event, in which case the original SF and
-- the event are used to build an new SF to switch into.
--
-- The switch is decoupled ('dSwitch').
--
-- See for more
-- information on how this switch works.
-- !!! Has not been optimized properly. Should be like kSwitch.
dkSwitch :: SF a b -> SF (a,b) (Event c) -> (SF a b -> c -> SF a b) -> SF a b
dkSwitch sf10@(SF {sfTF = tf10}) (SF {sfTF = tfe0}) k = SF {sfTF = tf0}
where
tf0 a0 =
let (sf1, b0) = tf10 a0
in (case tfe0 (a0, b0) of
(sfe, NoEvent) -> dkSwitchAux sf1 sfe
(_, Event c0) -> fst (sfTF (k sf10 c0) a0),
b0)
dkSwitchAux sf1 (SFArr _ (FDC NoEvent)) = sf1
dkSwitchAux sf1 sfe = SF' tf -- False
where
tf dt a =
let (sf1', b) = (sfTF' sf1) dt a
in (case (sfTF' sfe) dt (a, b) of
(sfe', NoEvent) -> dkSwitchAux sf1' sfe'
(_, Event c) -> fst (sfTF (k (freeze sf1 dt) c) a),
b)
------------------------------------------------------------------------------
-- Parallel composition and switching over collections with broadcasting
------------------------------------------------------------------------------
-- | Tuple a value up with every element of a collection of signal
-- functions.
broadcast :: Functor col => a -> col sf -> col (a, sf)
broadcast a = fmap (\sf -> (a, sf))
-- !!! Hmm. We should really optimize here.
-- !!! Check for Arr in parallel!
-- !!! Check for Arr FDE in parallel!!!
-- !!! Check for EP in parallel!!!!!
-- !!! Cf &&&.
-- !!! But how??? All we know is that the collection is a functor ...
-- !!! Maybe that kind of generality does not make much sense for
-- !!! par and parB? (Although it is niceto be able to switch into a
-- !!! par or parB from within a pSwitch[B].)
-- !!! If we had a parBList, that could be defined in terms of &&&, surely?
-- !!! E.g.
-- !!! parBList [] = constant []
-- !!! parBList (sf:sfs) = sf &&& parBList sfs >>> arr (\(x,xs) -> x:xs)
-- !!!
-- !!! This ought to optimize quite well. E.g.
-- !!! parBList [arr1,arr2,arr3]
-- !!! = arr1 &&& parBList [arr2,arr3] >>> arrX
-- !!! = arr1 &&& (arr2 &&& parBList [arr3] >>> arrX) >>> arrX
-- !!! = arr1 &&& (arr2 &&& (arr3 &&& parBList [] >>> arrX) >>> arrX) >>> arrX
-- !!! = arr1 &&& (arr2 &&& (arr3C >>> arrX) >>> arrX) >>> arrX
-- !!! = arr1 &&& (arr2 &&& (arr3CcpX) >>> arrX) >>> arrX
-- !!! = arr1 &&& (arr23CcpX >>> arrX) >>> arrX
-- !!! = arr1 &&& (arr23CcpXcpX) >>> arrX
-- !!! = arr123CcpXcpXcpX
-- | Spatial parallel composition of a signal function collection.
-- Given a collection of signal functions, it returns a signal
-- function that broadcasts its input signal to every element
-- of the collection, to return a signal carrying a collection
-- of outputs. See 'par'.
--
-- For more information on how parallel composition works, check
--
parB :: Functor col => col (SF a b) -> SF a (col b)
parB = par broadcast
-- | Parallel switch (dynamic collection of signal functions spatially composed
-- in parallel) with broadcasting. See 'pSwitch'.
--
-- For more information on how parallel composition works, check
--
pSwitchB :: Functor col =>
col (SF a b) -> SF (a,col b) (Event c) -> (col (SF a b)->c-> SF a (col b))
-> SF a (col b)
pSwitchB = pSwitch broadcast
-- | Decoupled parallel switch with broadcasting (dynamic collection of
-- signal functions spatially composed in parallel). See 'dpSwitch'.
--
-- For more information on how parallel composition works, check
--
dpSwitchB :: Functor col =>
col (SF a b) -> SF (a,col b) (Event c) -> (col (SF a b)->c->SF a (col b))
-> SF a (col b)
dpSwitchB = dpSwitch broadcast
-- | Recurring parallel switch with broadcasting.
--
-- Uses the given collection of SFs, until an event comes in the input, in
-- which case the function in the 'Event' is used to transform the collections
-- of SF to be used with 'rpSwitch' again, until the next event comes in the
-- input, and so on.
--
-- Broadcasting is used to decide which subpart of the input goes to each SF in
-- the collection.
--
-- See 'rpSwitch'.
--
-- For more information on how parallel composition works, check
--
rpSwitchB :: Functor col =>
col (SF a b) -> SF (a, Event (col (SF a b) -> col (SF a b))) (col b)
rpSwitchB = rpSwitch broadcast
-- | Decoupled recurring parallel switch with broadcasting.
--
-- Uses the given collection of SFs, until an event comes in the input, in
-- which case the function in the 'Event' is used to transform the collections
-- of SF to be used with 'rpSwitch' again, until the next event comes in the
-- input, and so on.
--
-- Broadcasting is used to decide which subpart of the input goes to each SF in
-- the collection.
--
-- This is the decoupled version of 'rpSwitchB'.
--
-- For more information on how parallel composition works, check
--
drpSwitchB :: Functor col =>
col (SF a b) -> SF (a, Event (col (SF a b) -> col (SF a b))) (col b)
drpSwitchB = drpSwitch broadcast
------------------------------------------------------------------------------
-- Parallel composition and switching over collections with general routing
------------------------------------------------------------------------------
-- | Spatial parallel composition of a signal function collection parameterized
-- on the routing function.
--
par :: Functor col =>
(forall sf . (a -> col sf -> col (b, sf))) -- ^ Determines the input to each signal function
-- in the collection. IMPORTANT! The routing function MUST
-- preserve the structure of the signal function collection.
-> col (SF b c) -- ^ Signal function collection.
-> SF a (col c)
par rf sfs0 = SF {sfTF = tf0}
where
tf0 a0 =
let bsfs0 = rf a0 sfs0
sfcs0 = fmap (\(b0, sf0) -> (sfTF sf0) b0) bsfs0
sfs = fmap fst sfcs0
cs0 = fmap snd sfcs0
in
(parAux rf sfs, cs0)
-- Internal definition. Also used in parallel switchers.
parAux :: Functor col =>
(forall sf . (a -> col sf -> col (b, sf)))
-> col (SF' b c)
-> SF' a (col c)
parAux rf sfs = SF' tf -- True
where
tf dt a =
let bsfs = rf a sfs
sfcs' = fmap (\(b, sf) -> (sfTF' sf) dt b) bsfs
sfs' = fmap fst sfcs'
cs = fmap snd sfcs'
in
(parAux rf sfs', cs)
-- | Parallel switch parameterized on the routing function. This is the most
-- general switch from which all other (non-delayed) switches in principle
-- can be derived. The signal function collection is spatially composed in
-- parallel and run until the event signal function has an occurrence. Once
-- the switching event occurs, all signal function are "frozen" and their
-- continuations are passed to the continuation function, along with the
-- event value.
--
-- !!! Could be optimized on the event source being SFArr, SFArrE, SFArrEE
pSwitch :: Functor col
=> (forall sf . (a -> col sf -> col (b, sf))) -- ^ Routing function: determines the input to each signal function
-- in the collection. IMPORTANT! The routing function has an
-- obligation to preserve the structure of the signal function
-- collection.
-> col (SF b c) -- ^ Signal function collection.
-> SF (a, col c) (Event d) -- ^ Signal function generating the switching event.
-> (col (SF b c) -> d -> SF a (col c)) -- ^ Continuation to be invoked once event occurs.
-> SF a (col c)
pSwitch rf sfs0 sfe0 k = SF {sfTF = tf0}
where
tf0 a0 =
let bsfs0 = rf a0 sfs0
sfcs0 = fmap (\(b0, sf0) -> (sfTF sf0) b0) bsfs0
sfs = fmap fst sfcs0
cs0 = fmap snd sfcs0
in
case (sfTF sfe0) (a0, cs0) of
(sfe, NoEvent) -> (pSwitchAux sfs sfe, cs0)
(_, Event d0) -> sfTF (k sfs0 d0) a0
pSwitchAux sfs (SFArr _ (FDC NoEvent)) = parAux rf sfs
pSwitchAux sfs sfe = SF' tf -- False
where
tf dt a =
let bsfs = rf a sfs
sfcs' = fmap (\(b, sf) -> (sfTF' sf) dt b) bsfs
sfs' = fmap fst sfcs'
cs = fmap snd sfcs'
in
case (sfTF' sfe) dt (a, cs) of
(sfe', NoEvent) -> (pSwitchAux sfs' sfe', cs)
(_, Event d) -> sfTF (k (freezeCol sfs dt) d) a
-- | Parallel switch with delayed observation parameterized on the routing
-- function.
--
-- The collection argument to the function invoked on the
-- switching event is of particular interest: it captures the
-- continuations of the signal functions running in the collection
-- maintained by 'dpSwitch' at the time of the switching event,
-- thus making it possible to preserve their state across a switch.
-- Since the continuations are plain, ordinary signal functions,
-- they can be resumed, discarded, stored, or combined with
-- other signal functions.
-- !!! Could be optimized on the event source being SFArr, SFArrE, SFArrEE.
--
dpSwitch :: Functor col =>
(forall sf . (a -> col sf -> col (b, sf))) -- ^ Routing function. Its purpose is
-- to pair up each running signal function in the collection
-- maintained by 'dpSwitch' with the input it is going to see
-- at each point in time. All the routing function can do is specify
-- how the input is distributed.
-> col (SF b c) -- ^ Initial collection of signal functions.
-> SF (a, col c) (Event d) -- ^ Signal function that observes the external
-- input signal and the output signals from the collection in order
-- to produce a switching event.
-> (col (SF b c) -> d -> SF a (col c)) -- ^ The fourth argument is a function that is invoked when the
-- switching event occurs, yielding a new signal function to switch
-- into based on the collection of signal functions previously
-- running and the value carried by the switching event. This
-- allows the collection to be updated and then switched back
-- in, typically by employing 'dpSwitch' again.
-> SF a (col c)
dpSwitch rf sfs0 sfe0 k = SF {sfTF = tf0}
where
tf0 a0 =
let bsfs0 = rf a0 sfs0
sfcs0 = fmap (\(b0, sf0) -> (sfTF sf0) b0) bsfs0
cs0 = fmap snd sfcs0
in
(case (sfTF sfe0) (a0, cs0) of
(sfe, NoEvent) -> dpSwitchAux (fmap fst sfcs0) sfe
(_, Event d0) -> fst (sfTF (k sfs0 d0) a0),
cs0)
dpSwitchAux sfs (SFArr _ (FDC NoEvent)) = parAux rf sfs
dpSwitchAux sfs sfe = SF' tf -- False
where
tf dt a =
let bsfs = rf a sfs
sfcs' = fmap (\(b, sf) -> (sfTF' sf) dt b) bsfs
cs = fmap snd sfcs'
in
(case (sfTF' sfe) dt (a, cs) of
(sfe', NoEvent) -> dpSwitchAux (fmap fst sfcs')
sfe'
(_, Event d) -> fst (sfTF (k (freezeCol sfs dt)
d)
a),
cs)
-- | Recurring parallel switch parameterized on the routing function.
--
-- Uses the given collection of SFs, until an event comes in the input, in
-- which case the function in the 'Event' is used to transform the collections
-- of SF to be used with 'rpSwitch' again, until the next event comes in the
-- input, and so on.
--
-- The routing function is used to decide which subpart of the input
-- goes to each SF in the collection.
--
-- This is the parallel version of 'rSwitch'.
rpSwitch :: Functor col
=> (forall sf . (a -> col sf -> col (b, sf))) -- ^ Routing function: determines the input to each signal function
-- in the collection. IMPORTANT! The routing function has an
-- obligation to preserve the structure of the signal function
-- collection.
-> col (SF b c) -- ^ Initial signal function collection.
-> SF (a, Event (col (SF b c) -> col (SF b c))) (col c)
rpSwitch rf sfs =
pSwitch (rf . fst) sfs (arr (snd . fst)) $ \sfs' f ->
noEventSnd >=- rpSwitch rf (f sfs')
{-
rpSwitch rf sfs = pSwitch (rf . fst) sfs (arr (snd . fst)) k
where
k sfs f = rpSwitch' (f sfs)
rpSwitch' sfs = pSwitch (rf . fst) sfs (NoEvent --> arr (snd . fst)) k
-}
-- | Recurring parallel switch with delayed observation parameterized on the
-- routing function.
--
-- Uses the given collection of SFs, until an event comes in the input, in
-- which case the function in the 'Event' is used to transform the collections
-- of SF to be used with 'rpSwitch' again, until the next event comes in the
-- input, and so on.
--
-- The routing function is used to decide which subpart of the input
-- goes to each SF in the collection.
--
-- This is the parallel version of 'drSwitch'.
drpSwitch :: Functor col
=> (forall sf . (a -> col sf -> col (b, sf))) -- ^ Routing function: determines the input to each signal function
-- in the collection. IMPORTANT! The routing function has an
-- obligation to preserve the structure of the signal function
-- collection.
-> col (SF b c) -- ^ Initial signal function collection.
-> SF (a, Event (col (SF b c) -> col (SF b c))) (col c)
drpSwitch rf sfs =
dpSwitch (rf . fst) sfs (arr (snd . fst)) $ \sfs' f ->
noEventSnd >=- drpSwitch rf (f sfs')
{-
drpSwitch rf sfs = dpSwitch (rf . fst) sfs (arr (snd . fst)) k
where
k sfs f = drpSwitch' (f sfs)
drpSwitch' sfs = dpSwitch (rf . fst) sfs (NoEvent-->arr (snd . fst)) k
-}
------------------------------------------------------------------------------
-- * Parallel composition/switchers with "zip" routing
------------------------------------------------------------------------------
-- | Parallel composition of a list of SFs.
--
-- Given a list of SFs, returns an SF that takes a list of inputs, applies
-- each SF to each input in order, and returns the SFs' outputs.
--
-- >>> embed (parZ [arr (+1), arr (+2)]) (deltaEncode 0.1 [[0, 0], [1, 1]])
-- [[1,2],[2,3]]
--
-- If there are more SFs than inputs, an exception is thrown.
--
-- >>> embed (parZ [arr (+1), arr (+1), arr (+2)]) (deltaEncode 0.1 [[0, 0], [1, 1]])
-- [[1,1,*** Exception: FRP.Yampa.Switches.parZ: Input list too short.
--
-- If there are more inputs than SFs, the unused inputs are ignored.
--
-- >>> embed (parZ [arr (+1)]) (deltaEncode 0.1 [[0, 0], [1, 1]])
-- [[1],[2]]
parZ :: [SF a b] -> SF [a] [b]
parZ = par (safeZip "parZ")
-- | Parallel switch (dynamic collection of signal functions spatially composed
-- in parallel). See 'pSwitch'.
--
-- For more information on how parallel composition works, check
--
pSwitchZ :: [SF a b] -> SF ([a],[b]) (Event c) -> ([SF a b] -> c -> SF [a] [b])
-> SF [a] [b]
pSwitchZ = pSwitch (safeZip "pSwitchZ")
-- | Decoupled parallel switch with broadcasting (dynamic collection of
-- signal functions spatially composed in parallel). See 'dpSwitch'.
--
-- For more information on how parallel composition works, check
--
dpSwitchZ :: [SF a b] -> SF ([a],[b]) (Event c) -> ([SF a b] -> c ->SF [a] [b])
-> SF [a] [b]
dpSwitchZ = dpSwitch (safeZip "dpSwitchZ")
-- | Recurring parallel switch with "zip" routing.
--
-- Uses the given list of SFs, until an event comes in the input, in which case
-- the function in the 'Event' is used to transform the list of SF to be used
-- with 'rpSwitchZ' again, until the next event comes in the input, and so on.
--
-- Zip routing is used to decide which subpart of the input goes to each SF in
-- the list.
--
-- See 'rpSwitch'.
--
-- For more information on how parallel composition works, check
--
rpSwitchZ :: [SF a b] -> SF ([a], Event ([SF a b] -> [SF a b])) [b]
rpSwitchZ = rpSwitch (safeZip "rpSwitchZ")
-- | Decoupled recurring parallel switch with "zip" routing.
--
-- Uses the given list of SFs, until an event comes in the input, in which case
-- the function in the 'Event' is used to transform the list of SF to be used
-- with 'rpSwitchZ' again, until the next event comes in the input, and so on.
--
-- Zip routing is used to decide which subpart of the input goes to each SF in
-- the list.
--
-- See 'rpSwitchZ' and 'drpSwitch'.
--
-- For more information on how parallel composition works, check
--
drpSwitchZ :: [SF a b] -> SF ([a], Event ([SF a b] -> [SF a b])) [b]
drpSwitchZ = drpSwitch (safeZip "drpSwitchZ")
-- IPerez: This is actually unsafezip. Zip is actually safe. It works
-- regardless of which list is smallest. This version of zip is right-biased:
-- the second list determines the size of the final list.
safeZip :: String -> [a] -> [b] -> [(a,b)]
safeZip fn l1 l2 = safeZip' l1 l2
where
safeZip' :: [a] -> [b] -> [(a, b)]
safeZip' _ [] = []
safeZip' as (b:bs) = (head' as, b) : safeZip' (tail' as) bs
head' :: [a] -> a
head' [] = err
head' (a:_) = a
tail' :: [a] -> [a]
tail' [] = err
tail' (_:as) = as
err :: a
err = usrErr "FRP.Yampa.Switches" fn "Input list too short."
-- Freezes a "running" signal function, i.e., turns it into a continuation in
-- the form of a plain signal function.
freeze :: SF' a b -> DTime -> SF a b
freeze sf dt = SF {sfTF = (sfTF' sf) dt}
freezeCol :: Functor col => col (SF' a b) -> DTime -> col (SF a b)
freezeCol sfs dt = fmap (`freeze` dt) sfs
-- | Apply an SF to every element of a list.
--
-- Example:
--
-- >>> embed (parC integral) (deltaEncode 0.1 [[1, 2], [2, 4], [3, 6], [4.0, 8.0 :: Float]])
-- [[0.0,0.0],[0.1,0.2],[0.3,0.6],[0.6,1.2]]
--
-- The number of SFs or expected inputs is determined by the first input
-- list, and not expected to vary over time.
--
-- If more inputs come in a subsequent list, they are ignored.
--
-- >>> embed (parC (arr (+1))) (deltaEncode 0.1 [[0], [1, 1], [3, 4], [6, 7, 8], [1, 1], [0, 0], [1, 9, 8]])
-- [[1],[2],[4],[7],[2],[1],[2]]
--
-- If less inputs come in a subsequent list, an exception is thrown.
--
-- >>> embed (parC (arr (+1))) (deltaEncode 0.1 [[0, 0], [1, 1], [3, 4], [6, 7, 8], [1, 1], [0, 0], [1, 9, 8]])
-- [[1,1],[2,2],[4,5],[7,8],[2,2],[1,1],[2,10]]
parC :: SF a b -> SF [a] [b]
parC sf = SF $ \as -> let os = map (sfTF sf) as
bs = map snd os
sfs = map fst os
in (parCAux sfs, bs)
-- Internal definition. Also used in parallel switchers.
parCAux :: [SF' a b] -> SF' [a] [b]
parCAux sfs = SF' tf
where
tf dt as =
let os = map (\(a,sf) -> sfTF' sf dt a) $ safeZip "parC" as sfs
bs = map snd os
sfcs = map fst os
in
(listSeq sfcs `seq` parCAux sfcs, listSeq bs)
listSeq :: [a] -> [a]
listSeq x = x `seq` (listSeq' x)
listSeq' :: [a] -> [a]
listSeq' [] = []
listSeq' rs@(a:as) = a `seq` listSeq' as `seq` rs
-- Vim modeline
-- vim:set tabstop=8 expandtab: