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To do

  • Many modules depend on ConCat.Circuit for AbsTy. Find another solution, perhaps via default methods with default signatures.
  • Define utility functions to do most of the work of various plugin transformations, including application, abstraction, pairing, etc.
  • Move (some?) todo items to github repo.
  • Look for a better solution to the problem of GHC eagerly inlining methods. My current workaround is ConCat.Category vs ConCat.AltCat. Inconvenient for adding classes (like ChoiceCat in ConCat.Choice). Could I instead recognize the dictionary selectors?
  • Mystery with RBin N3 vs expanded form. The former terminates, while the latter doesn't. See "fft_fc_octet" example in hardware/test/Examples.hs.
  • Failure with unboxed let bindings. See notes from 2017-07-15.
  • Principled replacement for the delay hack (defined in ConCat.Misc).
  • SMT depends on z3, which takes some work to install. Maybe disable SMT by default in concat-examples.cabal, with a flag to enable it.
  • I think the ghc-typelits-knownnat plugin works in GHCi. What's stopping concat-plugin from doing the same?
  • Automated testing.
  • Associated types for product, coproduct, exponential, Bool, Int, etc. The type of ccc will have to change, moving closer to the categorical notion of functor (and cartesian functor, closed cartesian functor, etc)
  • Users' guide / misc notes.
  • Document and begin fixing robustness issues.
  • Study performance, and begin improving:
    • AD seems rather slow. Perhaps due to lots of inlining and simplification.
  • Clean up & simplify implementation (once automated testing is in place), particularly ConCat.Plugin.
  • Translate case to DistribCat.
  • Categories/back-ends:
    • Verilog back-end, starting with the circuit graph category in ConCat.Circuit from concat and Circat.Netlist from circat. We'll need Float and Double literals, not currently supported by the KU netlist libraries.
    • Linear maps with native target representations rather than inlining.
    • GPU via CUDA or OpenCL, perhaps starting with the graph/circuit category (as with dot, Verilog, and GLSL)
    • Interval analysis (ConCat.Interval): more operations.
    • Polynomials
    • Probabilistic computation
    • Other Kleisli categories
    • JavaScript generation
    • Circuit graphs: rework with statically typed primitives.
      • Cleaner optimization
      • How to hash-cons?
    • GLSL: optimizations to introduce SIMD
    • Optimization, e.g., along the lines of z3cat.
    • Automatic differentiation:
      • Back-ends with explicit tensor representations. Experiment with associating composition.
      • ClosedCat instance?
    • A GUI category, along the lines of Tangible Functional Programming.
  • Improve treatment of coercions, replacing CoerceCat with composed uses of RepCat. (I've not managed to do so.)
  • CoproductCat instance in ConCat.Circuit.
  • Better use of GHC optimizations so that need less (ideally none) in ConCat.Circuit.
  • Recursion. Would help make a compelling case for compiling-to-categories vs deep DSLs.
  • Get rewrite rules to work better. Coercions and let bindings sometimes interfere.
  • Use dump-core (GitHub) to view generated Core.
  • Representation/levity polymorphism, so that we can used unboxed primitives, rather than having to reverse GHC unboxing work.

Misc to be reviewed

  • Compilation with AD is slow. Diagnose, and improve.
  • Maybe I should replace pin numbers by component numbers and output index (usually 0). I could perhaps identify components by a sequence of component indices within the ancestor chain, like stack frames.
  • Figure out how not to need orphan instances in AD and Incremental.
  • Better way to select orphan modules in runTcMUnsafe in BuildDictionary.
  • General TerminalCat default via ConstCat in Category. Revisit all TerminalCat instances.
  • Maybe I don't need ConstCat (:>) for anything but scalars, since the compiler will keep breaking down constant terms until it gets to a type for which the target category has a ConstCat instance.
  • Demand analysis at category.
  • Comment out PseudoFun annotations to see if anything breaks.
  • Use typeR from Misc to replace uses of typeRep. I don't think I'm still using typeRep.
  • In Plugin, refactor common functionality between "top" & "lam" transformations.
  • Name possibilities:
  • Maybe have buildDictionary accumulate error messages rather than selecting among them.
  • Sort out the problem with solving Coercible constraints as needed for CoerceCat (->). Came up with second derivatives. See 2017-01-01 notes, including note to Richard Eisenberg.
  • Larger tests, using shaped-types.
  • Remove old code from Plugin.
  • Add a test for derivatives without circuits, running the generated Haskell AD code.
  • Circuit: try making nodes for abst, repr, and coerce.
  • Restore the Coercible constraint in ConCat.Circuit, and figure out why the CoerceCat constraint isn't getting satisfied.
  • Does ConvertB work with constant propagation in ConCat.Circuit?
  • Why does the Coercible constraint suffice for CoerceCat in LinearRow but not in LinearCol?
  • Explore eliminating abstReprCase (and perhaps abstReprCon). Does unfolding suffice as an alternative? Not quite, since lambda-bound variables can appear as scrutinees. Maybe we could eliminate that possibility with another transformation.
  • After various optimizations, retry ADFun again for comparison.
  • Converting to the Trivial category leads to run-time error: "Impossible case alternative".
  • Rewrite rule loop involving "foo2" and "uncurry id" in AltCat.
  • In LinearRow and LinearCol, retry my old scaleL definition via Keyed and Adjustable, comparing for robustness and speed.
  • SPECIALIZE vector space and linear map operations for some common functors, particularly Par1, e.g., scaleL as used for numeric primitives.
  • In Plugin, factor out return (mkCcc (Lam x ...)) (for lam) and maybe also return (mkCcc ...) (for top).
  • Maybe switch from INLINE to INLINABLE.
  • Eliminate the hack of first cccing to (->), letting simplifications happen, and then cccing to another category, say without Closed. I think I'd have to improve my ability to do without Closed, including floating or substituting more let bindings.
  • I think I'll want to rename ProductCat, CoproductCat, and ClosedCat to "Cartesian", "Cocartesian", and "Closed". What about other Category subclasses?
  • There are case and let expressions in the middle of categorical compositions, where they can thwart CCC simplifications. Inlining those let expressions may be exactly what's needed to enable the simplifier's other transformations to eliminate the case expressions.
  • Simple, general treatment of ccc (\ _ -> U) as constFun (ccc u). Oops! Take care. If I have to $\eta$-expand U, I'll then get apply . (constFun (ccc U) &&& id). Needs more thought.
  • Look into work replication. See 2016-11-30 notes.
  • Better CCC optimization.
  • Why aren't the syntactic BoolCat, NumCat etc methods inlining, while the Category, and ProductCat ones are?
  • Other CCCs:
    • All CCCs (universally quantified)
    • Automatic differentiation
  • Fancier data types via HasRep or Control.Newtype.
  • More rule-based optimization.

Add more here as I encounter them.

Done

  • Add INLINE pragmas for the method defaults in ConCat.Category. So far, I've added them for just a few (***), subC, recipC, divideC. See personal notes for 2017-08-25.

  • Experiment with -fexpose-all-unfoldings as an alternative to explicit INLINE declarations. Also consider INLINABLE.

  • Add a plugin flag for showing the Core resulting of the plugin's pass.

  • Split concat into a few packages/repos:

    • Constrained categories ("concat")
    • The compiler plugin
    • Example categories and uses

    Make sure that it's easy & quick to build and run examples after the other packages change, without having to check in. For instance, use a stack.yaml with local package references.

  • Matches on Int literals lead to an error: "lam Case of boxer: bare unboxed var".

  • Fix the problem with finding numeric and show instances for Float & Double, and then simplify Circuit again to use 0 instead of Eql(fromIntegerZ 0), negate instead of negateZ, etc.

  • Remove ConCat.Float.

  • Reboxing of divideFloat# and divideDouble#. The rules in ConCat.Rebox (commented out) don't work, perhaps because those operations can fail. Simplest solution may be to rebox those primitives programmatically in another simple BuiltinRule.

  • Re-organize GAD and Incremental. Leave only general support in GAD, and move specific to AD and Incremental.

  • Try Coercion (from Data.Type.Coercion) as an example of constrained categories. Note that Coercion a b =~ Dict (Coercible a b). Similarly for (:~:) in Data.Type.Equality.

  • Track down problem with double example and deriv. Error message: "unFunB got unexpected bus ConvertB (<function>)". Happens when I use newtype instead of data for D in AD and drop HasL from OkLM in LinearRow. Fixed with a reveal added to dfun in AD.

  • Now that I'm unfolding more effectively (even with value args), maybe I no longer need the reveal hack. My first test in AD failed, but I may need to tweak unD' also. Update: I added reveal in dfun after ccc and before unD. Greatly improved simplification, and sped up compilation.

  • Pretty instances for GHC.Generics in Orphans.

  • Have buildDictionary yield an error message when it fails, replacing the Maybe return type with a sum. Then have Plugin display that message and terminate when appropriate.

  • In ConCat.Category, move Trivial and (:**:) to before Category, and move their class instances to just after each class definition, alongside (->).

  • Circuit: perhaps add a ReprB, and don't worry about canceling AbstB and ReprB.

  • Another idea about casts. Maybe I can operate not on the coercions but on their domain and range types as yielded by coercionKind. Then I wouldn't have to concoct sketchy coercions.

    • When domain and range agree, yield id.
    • If both are function types, use (<~) as now.
    • If the domain type has a HasRep instance, pre-compose repr, recursively "solving" for the other factor.
    • If the range type has a HasRep instance, post-compose abst, solving for other factor.

    I think this algorithm is the essence of what I'm doing now.

  • Move bottom-hiding unsafeCoerce hack from AltCat to a more general definition in Misc. Then use in AltCat for ccc.

  • Circuit: Eq and ConvertB. I'll probably have to switch to heterogeneous equality, perhaps via TestEquality in Data.Type.Equality. I'm not using Eq for now, so I've commented out the instance. Oh! Now that ConvertB requires Typeable, I can implement Eq via eqT.

  • Circuit: Try to unify AbstB and ConvertB. Might require changing abstC and reprC to be like abstC' and reprC', which would probably be fine.

  • Remove HERMIT dependency! I copied over HERMIT.GHC.Typechecker.

  • In recast, when handing AxiomInstCo and Sym variant, check for HasRep instances.

  • In Syn, use the pretty-printing class.

  • Undo the NOINLINE hack for numeric category operations, which is there for reboxing.

  • Find a way to localize the reboxing transformations (performing them only under ccc), so that they don't cause general slow-down. Then restore late inlining to AltCat ops.

  • Change the ConstCat Syn instance to pretty-print instead of showing, so that the layout logic works.

  • Move my transformations earlier, before stage zero, and make AltCat operations inline at stage zero.

  • Experiment with running the plugin much later. Try second to last. Use newtype-wrapped Int as well as Float and Double, scheduled to inline just after the plugin, i.e., phase 0. Hm. Given the deriving specification, can I delay inlining?

  • Add functions like sinFloat to monoInfo in Plugin.

  • Better solution for numeric operations on Float and Double, which don't work, perhaps due to orphan instances. My temporary workaround is Float.

  • In Plugin, try going directly from AxiomInstCo and SymCo AxiomInstCo to reprC and abstC. Failed.

  • Handle newtype better, and change some data uses back to newtype.

  • Fix transCatOp in Plugin to fail gracefully if the target category doesn't inhabit the needed Category subclass. Fall back to unfolding. Then fix the ConstCat (->) instance in Category, and replace P.const by const in Circuit and Lambda.

  • In Plugin, maybe float/subst when an expression is only used once. I think this one change would save a lot of work and lead to smaller CCC expressions.

  • Other CCCs:

    • A syntactic CCC for showing.
      • Use to test rule-based optimization.
      • I have a start in src/ConCat/Unused/.
      • Keep primitives simple, say as a string naming the primitive.
      • Try to do all optimization via GHC rules.
      • Would be nice to pretty-print rather than show.

  • Inspect categorical code, and start optimizing.

  • Work around problem with numeric operations on Float and Double. I added a module Float with Float and Double types that newtype-wrap the standard versions.

  • AD with non-scalar domains.