diff --git a/purescript/reverse-state/.vscode/settings.json b/purescript/reverse-state/.vscode/settings.json new file mode 100644 index 0000000..a90708f --- /dev/null +++ b/purescript/reverse-state/.vscode/settings.json @@ -0,0 +1,5 @@ +{ + "cSpell.words": [ + "purescript" + ] +} \ No newline at end of file diff --git a/purescript/reverse-state/LICENSE b/purescript/reverse-state/LICENSE new file mode 100644 index 0000000..1d258c7 --- /dev/null +++ b/purescript/reverse-state/LICENSE @@ -0,0 +1,339 @@ + GNU GENERAL PUBLIC LICENSE + Version 2, June 1991 + + Copyright (C) 1989, 1991 Free Software Foundation, Inc., + 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + Preamble + + The licenses for most software are designed to take away your +freedom to share and change it. By contrast, the GNU General Public +License is intended to guarantee your freedom to share and change free +software--to make sure the software is free for all its users. This +General Public License applies to most of the Free Software +Foundation's software and to any other program whose authors commit to +using it. (Some other Free Software Foundation software is covered by +the GNU Lesser General Public License instead.) You can apply it to +your programs, too. + + When we speak of free software, we are referring to freedom, not +price. Our General Public Licenses are designed to make sure that you +have the freedom to distribute copies of free software (and charge for +this service if you wish), that you receive source code or can get it +if you want it, that you can change the software or use pieces of it +in new free programs; and that you know you can do these things. + + To protect your rights, we need to make restrictions that forbid +anyone to deny you these rights or to ask you to surrender the rights. +These restrictions translate to certain responsibilities for you if you +distribute copies of the software, or if you modify it. + + For example, if you distribute copies of such a program, whether +gratis or for a fee, you must give the recipients all the rights that +you have. You must make sure that they, too, receive or can get the +source code. And you must show them these terms so they know their +rights. + + We protect your rights with two steps: (1) copyright the software, and +(2) offer you this license which gives you legal permission to copy, +distribute and/or modify the software. + + Also, for each author's protection and ours, we want to make certain +that everyone understands that there is no warranty for this free +software. If the software is modified by someone else and passed on, we +want its recipients to know that what they have is not the original, so +that any problems introduced by others will not reflect on the original +authors' reputations. + + Finally, any free program is threatened constantly by software +patents. We wish to avoid the danger that redistributors of a free +program will individually obtain patent licenses, in effect making the +program proprietary. To prevent this, we have made it clear that any +patent must be licensed for everyone's free use or not licensed at all. + + The precise terms and conditions for copying, distribution and +modification follow. + + GNU GENERAL PUBLIC LICENSE + TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION + + 0. This License applies to any program or other work which contains +a notice placed by the copyright holder saying it may be distributed +under the terms of this General Public License. The "Program", below, +refers to any such program or work, and a "work based on the Program" +means either the Program or any derivative work under copyright law: +that is to say, a work containing the Program or a portion of it, +either verbatim or with modifications and/or translated into another +language. (Hereinafter, translation is included without limitation in +the term "modification".) Each licensee is addressed as "you". + +Activities other than copying, distribution and modification are not +covered by this License; they are outside its scope. The act of +running the Program is not restricted, and the output from the Program +is covered only if its contents constitute a work based on the +Program (independent of having been made by running the Program). +Whether that is true depends on what the Program does. + + 1. You may copy and distribute verbatim copies of the Program's +source code as you receive it, in any medium, provided that you +conspicuously and appropriately publish on each copy an appropriate +copyright notice and disclaimer of warranty; keep intact all the +notices that refer to this License and to the absence of any warranty; +and give any other recipients of the Program a copy of this License +along with the Program. + +You may charge a fee for the physical act of transferring a copy, and +you may at your option offer warranty protection in exchange for a fee. + + 2. You may modify your copy or copies of the Program or any portion +of it, thus forming a work based on the Program, and copy and +distribute such modifications or work under the terms of Section 1 +above, provided that you also meet all of these conditions: + + a) You must cause the modified files to carry prominent notices + stating that you changed the files and the date of any change. + + b) You must cause any work that you distribute or publish, that in + whole or in part contains or is derived from the Program or any + part thereof, to be licensed as a whole at no charge to all third + parties under the terms of this License. + + c) If the modified program normally reads commands interactively + when run, you must cause it, when started running for such + interactive use in the most ordinary way, to print or display an + announcement including an appropriate copyright notice and a + notice that there is no warranty (or else, saying that you provide + a warranty) and that users may redistribute the program under + these conditions, and telling the user how to view a copy of this + License. (Exception: if the Program itself is interactive but + does not normally print such an announcement, your work based on + the Program is not required to print an announcement.) + +These requirements apply to the modified work as a whole. If +identifiable sections of that work are not derived from the Program, +and can be reasonably considered independent and separate works in +themselves, then this License, and its terms, do not apply to those +sections when you distribute them as separate works. But when you +distribute the same sections as part of a whole which is a work based +on the Program, the distribution of the whole must be on the terms of +this License, whose permissions for other licensees extend to the +entire whole, and thus to each and every part regardless of who wrote it. + +Thus, it is not the intent of this section to claim rights or contest +your rights to work written entirely by you; rather, the intent is to +exercise the right to control the distribution of derivative or +collective works based on the Program. + +In addition, mere aggregation of another work not based on the Program +with the Program (or with a work based on the Program) on a volume of +a storage or distribution medium does not bring the other work under +the scope of this License. + + 3. You may copy and distribute the Program (or a work based on it, +under Section 2) in object code or executable form under the terms of +Sections 1 and 2 above provided that you also do one of the following: + + a) Accompany it with the complete corresponding machine-readable + source code, which must be distributed under the terms of Sections + 1 and 2 above on a medium customarily used for software interchange; or, + + b) Accompany it with a written offer, valid for at least three + years, to give any third party, for a charge no more than your + cost of physically performing source distribution, a complete + machine-readable copy of the corresponding source code, to be + distributed under the terms of Sections 1 and 2 above on a medium + customarily used for software interchange; or, + + c) Accompany it with the information you received as to the offer + to distribute corresponding source code. (This alternative is + allowed only for noncommercial distribution and only if you + received the program in object code or executable form with such + an offer, in accord with Subsection b above.) + +The source code for a work means the preferred form of the work for +making modifications to it. For an executable work, complete source +code means all the source code for all modules it contains, plus any +associated interface definition files, plus the scripts used to +control compilation and installation of the executable. However, as a +special exception, the source code distributed need not include +anything that is normally distributed (in either source or binary +form) with the major components (compiler, kernel, and so on) of the +operating system on which the executable runs, unless that component +itself accompanies the executable. + +If distribution of executable or object code is made by offering +access to copy from a designated place, then offering equivalent +access to copy the source code from the same place counts as +distribution of the source code, even though third parties are not +compelled to copy the source along with the object code. + + 4. You may not copy, modify, sublicense, or distribute the Program +except as expressly provided under this License. Any attempt +otherwise to copy, modify, sublicense or distribute the Program is +void, and will automatically terminate your rights under this License. +However, parties who have received copies, or rights, from you under +this License will not have their licenses terminated so long as such +parties remain in full compliance. + + 5. You are not required to accept this License, since you have not +signed it. However, nothing else grants you permission to modify or +distribute the Program or its derivative works. These actions are +prohibited by law if you do not accept this License. Therefore, by +modifying or distributing the Program (or any work based on the +Program), you indicate your acceptance of this License to do so, and +all its terms and conditions for copying, distributing or modifying +the Program or works based on it. + + 6. Each time you redistribute the Program (or any work based on the +Program), the recipient automatically receives a license from the +original licensor to copy, distribute or modify the Program subject to +these terms and conditions. You may not impose any further +restrictions on the recipients' exercise of the rights granted herein. +You are not responsible for enforcing compliance by third parties to +this License. + + 7. If, as a consequence of a court judgment or allegation of patent +infringement or for any other reason (not limited to patent issues), +conditions are imposed on you (whether by court order, agreement or +otherwise) that contradict the conditions of this License, they do not +excuse you from the conditions of this License. If you cannot +distribute so as to satisfy simultaneously your obligations under this +License and any other pertinent obligations, then as a consequence you +may not distribute the Program at all. For example, if a patent +license would not permit royalty-free redistribution of the Program by +all those who receive copies directly or indirectly through you, then +the only way you could satisfy both it and this License would be to +refrain entirely from distribution of the Program. + +If any portion of this section is held invalid or unenforceable under +any particular circumstance, the balance of the section is intended to +apply and the section as a whole is intended to apply in other +circumstances. + +It is not the purpose of this section to induce you to infringe any +patents or other property right claims or to contest validity of any +such claims; this section has the sole purpose of protecting the +integrity of the free software distribution system, which is +implemented by public license practices. Many people have made +generous contributions to the wide range of software distributed +through that system in reliance on consistent application of that +system; it is up to the author/donor to decide if he or she is willing +to distribute software through any other system and a licensee cannot +impose that choice. + +This section is intended to make thoroughly clear what is believed to +be a consequence of the rest of this License. + + 8. If the distribution and/or use of the Program is restricted in +certain countries either by patents or by copyrighted interfaces, the +original copyright holder who places the Program under this License +may add an explicit geographical distribution limitation excluding +those countries, so that distribution is permitted only in or among +countries not thus excluded. In such case, this License incorporates +the limitation as if written in the body of this License. + + 9. The Free Software Foundation may publish revised and/or new versions +of the General Public License from time to time. Such new versions will +be similar in spirit to the present version, but may differ in detail to +address new problems or concerns. + +Each version is given a distinguishing version number. If the Program +specifies a version number of this License which applies to it and "any +later version", you have the option of following the terms and conditions +either of that version or of any later version published by the Free +Software Foundation. If the Program does not specify a version number of +this License, you may choose any version ever published by the Free Software +Foundation. + + 10. If you wish to incorporate parts of the Program into other free +programs whose distribution conditions are different, write to the author +to ask for permission. For software which is copyrighted by the Free +Software Foundation, write to the Free Software Foundation; we sometimes +make exceptions for this. Our decision will be guided by the two goals +of preserving the free status of all derivatives of our free software and +of promoting the sharing and reuse of software generally. + + NO WARRANTY + + 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY +FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN +OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES +PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED +OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF +MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS +TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE +PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, +REPAIR OR CORRECTION. + + 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING +WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR +REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, +INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING +OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED +TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY +YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER +PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE +POSSIBILITY OF SUCH DAMAGES. + + END OF TERMS AND CONDITIONS + + How to Apply These Terms to Your New Programs + + If you develop a new program, and you want it to be of the greatest +possible use to the public, the best way to achieve this is to make it +free software which everyone can redistribute and change under these terms. + + To do so, attach the following notices to the program. It is safest +to attach them to the start of each source file to most effectively +convey the exclusion of warranty; and each file should have at least +the "copyright" line and a pointer to where the full notice is found. + + + Copyright (C) 2020 Matei Adriel + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 2 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License along + with this program; if not, write to the Free Software Foundation, Inc., + 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. + +Also add information on how to contact you by electronic and paper mail. + +If the program is interactive, make it output a short notice like this +when it starts in an interactive mode: + + Gnomovision version 69, Copyright (C) year name of author + Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. + This is free software, and you are welcome to redistribute it + under certain conditions; type `show c' for details. + +The hypothetical commands `show w' and `show c' should show the appropriate +parts of the General Public License. Of course, the commands you use may +be called something other than `show w' and `show c'; they could even be +mouse-clicks or menu items--whatever suits your program. + +You should also get your employer (if you work as a programmer) or your +school, if any, to sign a "copyright disclaimer" for the program, if +necessary. Here is a sample; alter the names: + + Yoyodyne, Inc., hereby disclaims all copyright interest in the program + `Gnomovision' (which makes passes at compilers) written by James Hacker. + + , 1 April 1989 + Ty Coon, President of Vice + +This General Public License does not permit incorporating your program into +proprietary programs. If your program is a subroutine library, you may +consider it more useful to permit linking proprietary applications with the +library. If this is what you want to do, use the GNU Lesser General +Public License instead of this License. diff --git a/purescript/reverse-state/README.md b/purescript/reverse-state/README.md new file mode 100644 index 0000000..22b5a32 --- /dev/null +++ b/purescript/reverse-state/README.md @@ -0,0 +1,11 @@ +# Reverse state + +My experiments with reverse state in purescript. Here's a short proof of concept + +```purs +do + future <- get -- 4 + modify \a -> a * 2 + future' <- get -- 2 + put 2 +``` diff --git a/purescript/reverse-state/spago.dhall b/purescript/reverse-state/spago.dhall index a46c992..eb577b7 100644 --- a/purescript/reverse-state/spago.dhall +++ b/purescript/reverse-state/spago.dhall @@ -5,12 +5,12 @@ You can edit this file as you like. { name = "my-project" , dependencies = [ "console" + , "debug" , "effect" , "lazy" , "profunctor" , "psci-support" - , "run" - , "undefined" + , "transformers" ] , packages = ./packages.dhall , sources = [ "src/**/*.purs", "test/**/*.purs" ] diff --git a/purescript/reverse-state/src/BackwardsState.purs b/purescript/reverse-state/src/BackwardsState.purs new file mode 100644 index 0000000..cae9d5a --- /dev/null +++ b/purescript/reverse-state/src/BackwardsState.purs @@ -0,0 +1,51 @@ +module BackwardsState where + +import Prelude +import Control.MonadFix (class MonadFix, mfix) +import Data.Lazy (Lazy, force) +import Data.Lazy as Lazy +import Data.Newtype as Newtype +import Data.Profunctor.Strong (first) +import Data.Tuple (Tuple(..)) + +newtype BackwardsState s m a + = BackwardsState (Lazy s -> m (Tuple a (Lazy s))) + +runBackwardsState :: forall s m a. Functor m => BackwardsState s m a -> Lazy s -> m (Tuple a s) +runBackwardsState (BackwardsState run) s = run s <#> map force + +put :: forall s m. Monad m => s -> BackwardsState s m Unit +put s = BackwardsState \old -> pure $ Tuple unit (pure s) + +putLazy :: forall s m. Monad m => Lazy s -> BackwardsState s m Unit +putLazy s = BackwardsState \old -> pure $ Tuple unit s + +get :: forall m s. Monad m => BackwardsState s m (Lazy s) +get = BackwardsState \s -> pure $ Tuple s s + +modify :: forall m s. Monad m => (s -> s) -> BackwardsState s m Unit +modify f = BackwardsState \s -> pure $ Tuple unit (f <$> s) + +derive instance newtypeBackwardsState :: Newtype.Newtype (BackwardsState s m a) _ + +instance functorBS ∷ Functor m => Functor (BackwardsState s m) where + map = first >>> map >>> compose >>> Newtype.over BackwardsState + +instance applicativeBackwardsState :: MonadFix m => Applicative (BackwardsState s m) where + pure a = BackwardsState (\s -> pure $ Tuple a s) + +instance applyBackwardsState :: MonadFix m => Apply (BackwardsState s m) where + apply = ap + +instance bindBackwardsState :: MonadFix m => Bind (BackwardsState s m) where + bind (BackwardsState run) f = + BackwardsState \state -> + _.results + <$> mfix \lazy -> do + (Tuple presentValue presentState) <- + run + $ Lazy.defer \_ -> force $ _.future $ lazy unit + (Tuple futureValue futureState) <- Newtype.unwrap (f presentValue) state + pure { results: Tuple futureValue presentState, future: futureState } + +instance monadBackwardsState :: MonadFix m => Monad (BackwardsState s m) diff --git a/purescript/reverse-state/src/Control/MonadFix.js b/purescript/reverse-state/src/Control/MonadFix.js new file mode 100644 index 0000000..4573ee5 --- /dev/null +++ b/purescript/reverse-state/src/Control/MonadFix.js @@ -0,0 +1,33 @@ +/* global exports, require */ +"use strict"; + +////////////////////////////////////////////////////////////////// +// ATTRIBUTION +// monad-fix package is not on pursuit, so copied this file from - +// https://github.com/zrho/purescript-monad-fix/ +////////////////////////////////////////////////////////////////// + +// module Control.MonadFix + +var message = "Control.MonadFix: Premature access to result of fixpoint computation." + +// fixEffect :: forall eff a. ((Unit -> a) -> Eff eff a) -> Eff eff a +exports.fixEffect = function(f) { + return function() { + var result = null; + var ready = false; + + result = f(function(u) { + if (!ready) throw new Error(message); + return result; + })(); + + ready = true; + return result; + } +} + +// fixPure :: forall a. ((Unit -> a) -> a) -> a +exports.fixPure = function(f) { + return exports.fixEffect(function(a) { return function () { return f(a); }})(); +} diff --git a/purescript/reverse-state/src/Control/MonadFix.purs b/purescript/reverse-state/src/Control/MonadFix.purs new file mode 100644 index 0000000..6c6c21f --- /dev/null +++ b/purescript/reverse-state/src/Control/MonadFix.purs @@ -0,0 +1,50 @@ +module Control.MonadFix where + +------------------------------------------------------------------ +-- ATTRIBUTION +-- monad-fix package is not on pursuit, so copied this file from - +-- https://github.com/zrho/purescript-monad-fix/ +------------------------------------------------------------------ + +import Prelude + +import Control.Monad.RWS.Trans (RWST(..), RWSResult(..), runRWST) +import Control.Monad.Reader.Trans (ReaderT(..), runReaderT) +import Control.Monad.State.Trans (StateT(..), runStateT) +import Control.Monad.Writer.Trans (WriterT(..), runWriterT) +import Data.Identity (Identity(..)) +import Data.Newtype (unwrap) +import Data.Tuple (fst) +import Effect (Effect) + +foreign import fixEffect :: forall a. ((Unit -> a) -> Effect a) -> Effect a +foreign import fixPure :: forall a. ((Unit -> a) -> a) -> a + +-- | Type class for monads that support fixpoints. +-- | +-- | `mfix f` runs `f` once with the eventual result of `f` as input. Make sure +-- | not to apply the supplied function until the computation returned; else +-- | a dynamic error will be thrown. +class (Monad m) <= MonadFix m where + mfix :: forall a. ((Unit -> a) -> m a) -> m a + +instance monadFixRWST :: (Monoid w, MonadFix m) => MonadFix (RWST r w s m) where + mfix f = RWST \r s -> mfix \t -> runRWST (f \u -> case t u of RWSResult _ a _ -> a) r s + +instance monadFixIdentity :: MonadFix Identity where + mfix = Identity <<< fixPure <<< (unwrap <<< _) + +instance monadFixEff :: MonadFix Effect where + mfix = fixEffect + +instance monadFixFunction :: MonadFix (Function r) where + mfix f r = fixPure (flip f r) + +instance monadFixReaderT :: (MonadFix m) => MonadFix (ReaderT r m) where + mfix f = ReaderT \r -> mfix (flip runReaderT r <<< f) + +instance monadFixStateT :: (MonadFix m) => MonadFix (StateT s m) where + mfix f = StateT \s -> mfix (flip runStateT s <<< f <<< (fst <<< _)) + +instance monadFixWriterT :: (MonadFix m, Monoid w) => MonadFix (WriterT w m) where + mfix f = WriterT $ mfix (runWriterT <<< f <<< (fst <<< _)) diff --git a/purescript/reverse-state/src/Fix.purs b/purescript/reverse-state/src/Fix.purs deleted file mode 100644 index 92e7b0f..0000000 --- a/purescript/reverse-state/src/Fix.purs +++ /dev/null @@ -1,120 +0,0 @@ -module Fix where - -import Prelude -import Control.Lazy (fix) -import Data.Either (Either(..)) -import Data.Lazy (defer) -import Data.Lazy as Lazy -import Data.Symbol (class IsSymbol) -import Data.Traversable (sequence) -import Data.Tuple (Tuple) -import Prim.Row as Row -import Run (FProxy, Run, SProxy(..), VariantF) -import Run as Run -import Undefined (undefined) - -data BackwardsState s a - = BackwardsState (s -> s) (s -> a) - -derive instance functorBS ∷ Functor (BackwardsState s) - -type BACKWARDS_STATE s - = FProxy (BackwardsState s) - -_backwardsState ∷ SProxy "backwardsState" -_backwardsState = SProxy - -liftBackwardsState ∷ forall s a r. BackwardsState s a → Run ( backwardsState ∷ BACKWARDS_STATE s | r ) a -liftBackwardsState = liftBackwardsStateAt _backwardsState - -liftBackwardsStateAt ∷ - forall t state a r label. - IsSymbol label ⇒ - Row.Cons label (BACKWARDS_STATE state) t r ⇒ - SProxy label → - BackwardsState state a → - Run r a -liftBackwardsStateAt = Run.lift - -runBackwardsStateAt :: - forall label state rowWithState row a. - IsSymbol label ⇒ - Row.Cons label (BACKWARDS_STATE state) row rowWithState ⇒ - SProxy label → - state → - Run rowWithState a → - Run row (Tuple state a) -runBackwardsStateAt sym = undefined - where - handle :: - forall b. - VariantF rowWithState - (Run rowWithState b) -> - Either (BackwardsState state (Run rowWithState b)) (VariantF row (Run rowWithState b)) - handle = Run.on sym Left Right - - mkLoop :: - forall result acc b. - ( acc -> - (BackwardsState state (Run rowWithState b)) -> - Run row result - ) -> - (acc -> b -> result) -> acc -> Run rowWithState b -> Run row result - mkLoop handleState handleResult accumulated r = case Run.peel r of - Left peeled → case handle peeled of - Left bs → handleState accumulated bs - Right a' → Run.send a' >>= mkLoop handleState handleResult accumulated - Right result → pure $ handleResult accumulated result - - loopState :: Lazy.Lazy state -> Run rowWithState Unit -> Run row (Lazy.Lazy state) - loopState = mkLoop handleState handleResult - where - {- - past = ... - present <- mkState future - future <- mkState past - -} - handleState :: state -> BackwardsState state (Run rowWithState Unit) -> Run row (Lazy.Lazy state) - handleState state (BackwardsState mkState mkValue) = - sequence do - (futureState :: Run _ _) <- - fix \m -> do - (futureState :: Run _ _) <- m - let - value :: Run _ _ - value = mkValue <$> futureState - - state' :: Run _ (Lazy.Lazy state) - state' = value >>= loopState state - pure - state' - pure (mkState <$> futureState) - - handleResult = const - - -- case Run.peel r of - -- Left a → case handle a of - -- Left (BackwardsState mkState _) → do - -- resultState <- loopState state - -- pure (mkState futureState) - -- Right a' → b >>= f - -- where - -- f = runBackwardsStateAt sym s - -- b = Run.send a' - -- Right a → pure (Tuple s a) - -- loop :: state -> Run rowWithState a -> Run row (Tuple state a) - -- loop s r = case Run.peel r of - -- Left a → case handle a of - -- Left (BackwardsState mkState mkValue) → do - -- let - -- value = mkValue resultState - -- (Tuple resultState resultValue) <- loop s value - -- pure $ Tuple (mkState futureState) resultValue - -- Right a' → b >>= f - -- where - -- f :: Run rowWithState a -> Run row (Tuple state a) - -- f = runBackwardsStateAt sym s - -- b :: Run row (Run rowWithState a) - -- b = Run.send a' - -- Right a → pure (Tuple s a) - a = 3 diff --git a/purescript/reverse-state/src/Main.purs b/purescript/reverse-state/src/Main.purs index 5c18dca..4ef5c3d 100644 --- a/purescript/reverse-state/src/Main.purs +++ b/purescript/reverse-state/src/Main.purs @@ -1,10 +1,30 @@ module Main where import Prelude - +import BackwardsState (BackwardsState, get, modify, put, runBackwardsState) +import Control.Monad.Reader (Reader, runReader) +import Data.Lazy (Lazy, force) +import Data.Tuple (fst, snd) import Effect (Effect) +import Effect.Class.Console (logShow) import Effect.Console (log) +type LabM a + = BackwardsState Int (Reader String) (Lazy a) + +state :: LabM Int +state = do + future <- get -- 4 + modify \a -> a * 2 + future' <- get -- 2 + put 2 + pure future + main :: Effect Unit main = do - log "🍝" + let + r = flip runReader "env" $ runBackwardsState state $ pure 0 + log "State:" + logShow (snd r) + log "Result:" + logShow (force $ fst r)