symantic/symantic.cabal

   1 author: Julien Moutinho <julm+symantic@autogeree.net>
   2 bug-reports: Julien Moutinho <julm+symantic@autogeree.net>
   3 build-type: Simple
   4 cabal-version: >= 1.24
   5 category: Language
   6 description:
   7  __Description__
   8  .
   9  This is an experimental library for composing, parsing, typing, compiling, transforming and interpreting
  10  a custom DSL (Domain-Specific Language) expressing
  11  a subset of GHC's Haskell type system:
  12  .
  13  * /first class functions/ (aka. /lambdas/),
  14  * chosen /monomorphic types/ (like 'Bool' or 'Maybe'),
  15  * chosen /rank-1 polymorphic types/ (like @(@'Maybe'@ a)@),
  16  * chosen /type class instances/,
  17  * chosen /type family instances/,
  18  * and chosen /type constraints/;
  19  .
  20  where "chosen X" means declared in Haskell
  21  and selected when composing the DSL.
  22  .
  23  In particular, this library is currently not able to:
  24  .
  25  * do /type inferencing/ for the argument of /lambdas/
  26    (they must all be explicitely annotated, aka. /Church-style/),
  27  * do /pattern matching/ (aka. /case/) (but /Church-encoding/ functions are often enough),
  28  * do /rank-N polymorphic types/ (aka. /non-prenex forall/, like @(forall s. ST s a) -> a@).
  29  .
  30  And by itself, the DSL is only able to define new terms to be interpreted,
  31  no new types, or other type-level structures.
  32  .
  33  __Warning__
  34  .
  35  Please be aware that despite its using of powerful ideas from clever people,
  36  this remains a FUND-LESS SINGLE-PERSON EXPERIMENTAL LIBRARY.
  37  Meaning that it IS NOT heavily tested and documented,
  38  DOES NOT have a strong commitment to preserving backward compatibility,
  39  MAY FAIL to comply with the <http://www.haskell.org/haskellwiki/Package_versioning_policy PVP>,
  40  and CAN die without notice.
  41  You've been warned.
  42  .
  43  __Use cases__
  44  .
  45  The main goal of this library is to enable the runtime interpretation of terms,
  46  type-checked according to some types defined at composing-time (ie. GHC's compile-time).
  47  .
  48  Using a DSL enables to limit expressiveness in order to ease analysis.
  49  Here the idea is that the more complex logic shall remain written in Haskell,
  50  and then this library used to project an interface into a DSL
  51  (using GHC's Haskell as a FFI (Foreign Function Interface)).
  52  This in order to give runtime users the flexibility
  53  to write programs not requiring a full-blown Haskell compiler,
  54  yet enabling enough flexibility to let them express complex needs
  55  with a reasonably advanced type-safe way
  56  and a controlled environment of primitives.
  57  .
  58  Typical use cases:
  59  .
  60  * Enabling runtime users to enter some Haskell-like expressions
  61    (maybe with a more convenient syntax wrt. the domain problem)
  62    without using at runtime all the heavy machinery and ecosystem of GHC
  63    (eg. by using <https://hackage.haskell.org/package/hint hint>),
  64    but still leaning on primitive functions coded in GHC's Haskell.
  65  * Limiting those expressions to be built from well-controlled expressions only.
  66  * Run some analyzes/optimizations on those well-controlled expressions.
  67  .
  68  __Usage__
  69  .
  70  Please pick in <https://hackage.haskell.org/package/symantic-lib symantic-lib>
  71  a few specific @Lib/*.hs@ files near what you want to do
  72  and the corresponding @Lib\/*/Test.hs@ file,
  73  if any in the <git://git.autogeree.net/symantic Git repository>,
  74  to learn by examples how to use this library.
  75  .
  76  Those @Lib\/*/Test.hs@ files use <https://hackage.haskell.org/package/megaparsec megaparsec> as parser
  77  (see @Grammar/Megaparsec.hs@) and a default grammar somehow sticking to Haskell's,
  78  but staying context-free (so in particular: insensitive to the indentation),
  79  and supporting prefix and postfix operators.
  80  This grammar — itself written as a symantic embedded DSL
  81  with <https://hackage.haskell.org/package/symantic-grammar symantic-grammar> —
  82  can be reused to build other ones, is not bound to a specific parser,
  83  and can produce its own EBNF rendition.
  84  .
  85  __Acknowledgements__
  86  .
  87  This library would probably be much worse than it is
  88  without the following seminal works:
  89  .
  90  * <http://okmij.org/ftp/tagless-final/ Finally Tagless> by Jacques Carette, Oleg Kiselyov, and Chung-chieh Shan.
  91  * <http://cs.brynmawr.edu/~rae/papers/2016/thesis/eisenberg-thesis.pdf Dependent Types in Haskell> by Richard A. Eisenberg.
  92  .
  93  __Main ideas__
  94  .
  95  * __Symantic DSL__.
  96    Terms are encoded in the <http://okmij.org/ftp/tagless-final/ Tagless-Final> way (aka. the /symantic/ way)
  97    which leverages the /type class/ system of Haskell — instead of using /data types/ — to form an embedded DSL.
  98    More specifically, a /class/ encodes the /syntax/ of terms (eg. 'Sym_Bool')
  99    and its /class instances/ on a dedicated type encodes their /semantics/
 100    (eg. @(Sym_Bool Eval)@ interprets a term as a value of its type
 101    in the host language ('Bool' in Haskell here),
 102    or @(Sym_Bool View)@ interprets a term as a textual rendition, etc.).
 103
 104    DSL are then composed/extended by selecting those symantic /classes/
 105    (and in an embedded DSL those could even be automatically inferred,
 106    when @NoMonomorphismRestriction@ is on).
 107    Otherwise, when using symantics for a non-embedded DSL
 108    — the whole point of this library — the /classes/ composing the DSL
 109    are selected manually at GHC's compile-time,
 110    through the /type-level list/ @ss@ given to 'readTerm'.
 111
 112    Moreover, those symantic @term@s are parameterized by the type of the value they encode,
 113    in order to get the same type safety as with plain Haskell values.
 114    Hence the symantic /classes/ have the higher kind: @((* -> *) -> Constraint)@
 115    instead of just @(* -> Constraint)@.
 116
 117    Amongst those symantics, 'Sym_Lambda' introduces /lambda abstractions/ by an higher-order approach,
 118    meaning that they directly reuse GHC's internal machinery
 119    to abstract or instantiate variables,
 120    which I think is by far the most efficient and simplest way of doing it
 121    (no (generalized or not) DeBruijn encoding
 122    like in <https://hackage.haskell.org/package/bound bound>'s @Monad@s).
 123
 124  * __Singleton for any type__.
 125    To typecheck terms using a @(@'Type'@ src vs t)@ which acts as a /singleton type/
 126    for any Haskell /type index/ @t@ of any kind,
 127    which is made possible with the dependant Haskell extensions:
 128    especially @TypeFamilies@, @GADTs@ and @TypeInType@.
 129
 130  * __Type constants using 'Typeable'__.
 131    /Type constant/ could be introduced by indexing them amongst a /type-level list/,
 132    but since they are /monomorphic types/, using 'Typeable' simplifies
 133    the machinery, and is likely more space/time efficient, including at GHC-compile-time.
 134
 135  * __Type variables using a type-level list__.
 136    Handling /type variables/ is done by indexing them amongst a @vs@ /type-level list/,
 137    where each /type variable/ is wrapped inside a @Proxy@ to handle different kinds.
 138    Performing a substitution (in 'substVar') preserves the /type index/ @t@,
 139    which is key for preserving any associated 'Term'.
 140    Unifying /type variables/ is done with 'unsafeCoerce' (in 'unifyType'),
 141    which I think is necessary and likely safe.
 142
 143  -- NOTE: no longer used.
 144  -- * __Extensible data type__.
 145  --   To inject a type into a /type-level list/
 146  --   or project a /type-level list/ onto a type,
 147  --   to compose an /extensible data type/
 148  --   (eg. the 'Token' @GADT@ gathering the 'TokenT' /data instances/,
 149  --   that a parser can build and then give to 'compile').
 150  --   This type-level programming requires @UndecidableInstances@,
 151  --   but not @OverlappingInstances@.
 152  --
 153  --   There is a similarity with
 154  --   <http://dx.doi.org/10.1017/S0956796808006758 Data types à la carte>
 155  --   (see for instance <https://hackage.haskell.org/package/compdata compdata>
 156  --   or <https://hackage.haskell.org/package/syntactic syntactic>).
 157  --   Those also enable to compose a DSL using some machinery
 158  --   based upon (co)free(r) (co)monads and (cata|ana)morphisms.
 159  --   Which library fits best your problem domain and brain is for you to judge :)
 160  --   On that topic, see also:
 161  --   <https://www.youtube.com/watch?v=qaAKRxO21fU Stop Paying for Free Monads>.
 162  --
 163  -- Here, I just came up using /type-level lists/ by hacking
 164  -- <https://hackage.haskell.org/package/glambda glambda>'s @Elem@.
 165  .
 166  __Main extensions__
 167  .
 168  * @ConstraintKinds@ for /type lists/ to contain 'Constraint's,
 169    or reifying any 'Constraint' as an explicit dictionary 'Dict',
 170    or defining /type synonym/ of /type classes/,
 171    or merging /type constraints/.
 172  * @DataKinds@ for type-level data structures (eg. /type-level lists/).
 173  * @DefaultSignatures@ for providing identity transformations of terms,
 174    and thus avoid boilerplate code when a transformation
 175    does not need to alter all semantics.
 176    Almost as explained in <https://ro-che.info/articles/2016-02-03-finally-tagless-boilerplate Reducing boilerplate in finally tagless style>.
 177  * @GADTs@ for knowing types by pattern-matching terms,
 178    or building terms by using type classes.
 179  * @PolyKinds@ for avoiding a lot of uses of 'Proxy'.
 180  * @Rank2Types@ or @ExistentialQuantification@ for parsing @GADT@s.
 181  * @TypeApplications@ for having a more concise syntax
 182    to build 'Type' (eg. 'tyConst'@ @\@Bool).
 183  * @TypeFamilies@ for type-level programming.
 184  * @TypeInType@ (introduced in GHC 8.0.1)
 185    for 'Type' to also bind a kind equality for the type @t@ it encodes.
 186    Which makes the /type application/ ('TyApp')
 187    give us an /arrow kind/ for the Haskell /type constructor/
 188    it applies an Haskell type to, releaving me from tricky workarounds.
 189  * @UndecidableInstances@ for type-level programming that may never terminate.
 190  .
 191  __Bugs__
 192  .
 193  There are some of them hidding in there,
 194  and the whole thing is far from being perfect…
 195  Your comments, problem reports, or questions, are welcome!
 196  You have my email address, so… just send me some emails :]
 197  .
 198  __To do__
 199  .
 200  * Study to which point /type inferencing/ is doable,
 201    now that 'Type' is powerful enough to contain 'TyVar's.
 202  * Study to which point error messages can be improved,
 203    now that there is a 'Source' carried through all 'Kind's or 'Type's,
 204    it should enable some nice reports.
 205    Still, a lot of work and testing remain to be done,
 206    and likely some ideas to find too…
 207  * Add more terms in <https://hackage.haskell.org/package/symantic-lib symantic-lib>.
 208  * Add more transformations.
 209  * Study how to integrate types into the module system.
 210  * Study where to put @INLINE@, @INLINEABLE@ or @SPECIALIZE@ pragmas.
 211  * Study how to support /rank-N polymorphic types/,
 212    special cases can likely use the /boxed polymorphism/ workaround,
 213    but even if GHC were supporting /impredicative types/,
 214    I'm currently clueless about how to do this.
 215 extra-source-files:
 216 extra-tmp-files:
 217 -- homepage:
 218 license: GPL-3
 219 license-file: COPYING
 220 maintainer: Julien Moutinho <julm+symantic@autogeree.net>
 221 name: symantic
 222 stability: experimental
 223 synopsis: Library for Typed Tagless-Final Higher-Order Composable DSL
 224 tested-with: GHC==8.0.2
 225 -- PVP:  +-+------- breaking API changes
 226 --       | | +----- non-breaking API additions
 227 --       | | | +--- code changes with no API change
 228 version: 6.0.0.20170618
 229
 230 Source-Repository head
 231   location: git://git.autogeree.net/symantic
 232   type:     git
 233
 234 Library
 235   default-extensions:
 236     DataKinds
 237     DefaultSignatures
 238     FlexibleContexts
 239     FlexibleInstances
 240     LambdaCase
 241     MultiParamTypeClasses
 242     NamedFieldPuns
 243     OverloadedStrings
 244     Rank2Types
 245     ScopedTypeVariables
 246     StandaloneDeriving
 247     TupleSections
 248     TypeApplications
 249     TypeFamilies
 250     TypeOperators
 251   ghc-options: -Wall
 252                -fno-warn-tabs
 253   default-language: Haskell2010
 254   exposed-modules:
 255     Language.Symantic
 256     Language.Symantic.Compiling
 257     Language.Symantic.Compiling.Beta
 258     Language.Symantic.Compiling.Grammar
 259     Language.Symantic.Compiling.Module
 260     Language.Symantic.Compiling.Read
 261     Language.Symantic.Compiling.Term
 262     Language.Symantic.Interpreting
 263     Language.Symantic.Interpreting.Dup
 264     Language.Symantic.Interpreting.Eval
 265     Language.Symantic.Interpreting.View
 266     Language.Symantic.Transforming
 267     Language.Symantic.Transforming.Beta
 268     Language.Symantic.Transforming.Trans
 269     Language.Symantic.Typing
 270     Language.Symantic.Typing.Document
 271     Language.Symantic.Typing.Grammar
 272     Language.Symantic.Typing.Kind
 273     Language.Symantic.Typing.List
 274     Language.Symantic.Typing.Peano
 275     Language.Symantic.Typing.Read
 276     Language.Symantic.Typing.Show
 277     Language.Symantic.Typing.Type
 278     Language.Symantic.Typing.Unify
 279     Language.Symantic.Typing.Variable
 280   build-depends:
 281     base >= 4.6 && < 5
 282     , containers
 283     , ghc-prim
 284     , mono-traversable
 285     , symantic-grammar
 286     , symantic-document
 287     , transformers
 288     , text