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@camilstaps camilstaps/dyn.icl
Last active Feb 18, 2018

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Monomorphic dynamics without language support
module dyn
import StdEnv
import Data.Maybe
:: Type
= Cons String
| App Type Type
instance == Type
where
== (Cons s) (Cons t) = s == t
== (App t u) (App p q) = t == p && u == q
== _ _ = False
:: Dyn = E.v:
{ val :: v
, type :: Type
}
class type a :: a -> Type
instance type Int where type _ = Cons "Int"
instance type Bool where type _ = Cons "Bool"
instance type Char where type _ = Cons "Char"
instance type Real where type _ = Cons "Real"
instance type (a,b) | type a & type b
where
type t = App (App (Cons "_Tuple2") (type x)) (type y)
where [(x,y):_] = [undef,t]
instance type [a] | type a
where
type xs = App (Cons "_List") (type x)
where [x:_] = [undef:xs]
instance type (a -> b) | type a & type b
where
type f = App (App (Cons "->") (type i)) (type r)
where
i = undef
[r:_] = [undef,f i]
pack :: a -> Dyn | type a
pack x = {val=x, type=type x}
unpack :: Dyn -> Maybe a | type a
unpack dyn = unpack` undef dyn
where
unpack` :: a Dyn -> Maybe a | type a
unpack` x dyn
| type x == dyn.type = cast Just dyn.val
| otherwise = Nothing
cast :: !u:a -> u:b
cast _ = code {
no_op
}
Start :: Maybe (Int -> Int)
Start = unpack (pack square)
square :: Int -> Int
square x = x * x
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