]> Git — Sourcephile - haskell/symantic.git/blob - symantic/Language/Symantic/Transforming/Beta.hs
Massive rewrite to better support rank-1 polymorphic types.
[haskell/symantic.git] / symantic / Language / Symantic / Transforming / Beta.hs
1 {-# LANGUAGE GADTs #-}
2 -- | Interpreter to beta-reduce static lambdas
3 -- introduced only because of the compiling machinery
4 -- (hence preserving lambdas put by the user).
5 module Language.Symantic.Transforming.Beta where
6
7 import Language.Symantic.Transforming.Trans
8 import Language.Symantic.Compiling.Term
9
10 -- * Type 'BetaT'
11 -- | The annotation here is if a lambda is known statically,
12 -- and so can be applied if given an argument,
13 -- Moreover, it only does this beta-reduction if the lambda
14 -- has been introduced by the compiling phase
15 -- (which happens when a symantic method is a function
16 -- between 'term's instead of being only a 'term')
17 -- (i.e. 'lam1' is used, not 'lam')
18 data BetaT term a where
19 BetaT_Unk :: term a -> BetaT term a
20 BetaT_Lam1 :: (BetaT term a -> BetaT term b) -> BetaT term (a -> b)
21
22 instance Sym_Lambda term => Trans (BetaT term) where
23 type UnT (BetaT term) = term
24 trans = BetaT_Unk
25 unTrans (BetaT_Unk t) = t
26 unTrans (BetaT_Lam1 f) = lam1 $ unTrans . f . trans
27
28 -- | 'lam1' adds annotations, 'app' uses it
29 instance Sym_Lambda term => Sym_Lambda (BetaT term) where
30 lam1 = BetaT_Lam1 -- NOTE: only 'lam1' introduces 'BetaT_Lam1', not 'lam'.
31 app (BetaT_Lam1 f) = f
32 app f = trans2 app f
33 let_ x f = trans $ let_ (unTrans x) (unTrans . f . trans)
34
35 -- | Transformer
36 betaT :: Trans (BetaT term) => BetaT term a -> term a
37 betaT = unTrans