-- File: lambdaLplus

-- This file selects the DPTS lambda-omega-L-plus, i.e. the extension of
-- lambda-omega-L with records and existential types.
-- Records are built-in in Yarrow, and are activated below by the System
-- command.
-- Existential types are not built-in in Yarrow, but are introduced with
-- their usual second-order encoding.

Path "../lol"
Load "logic"

-- Existential datatypes will be expressed using Sig.
Def Sig := \I:*s->*s. @Y:*s. (@X:*s. I X -> Y) -> Y  : (*s->*s)->*s
Binder Sig

Def pack := \I:*s->*s. \Rep:*s. \imp: I Rep. \Y:*s. \a:(@X:*s.I X->Y).
                       a Rep imp : 
            @I:*s->*s. @Rep:*s. I Rep -> (Sig X:*s. I X)
LatexVar 3 pack

Def unpack := \I:*s->*s. \T:*s. \adt: Sig X:*s.I X. \m: @Rep:*s. I Rep -> T.
                    adt T m : 
              @I:*s->*s. @T:*s. (Sig X:*s.I X) -> (@Rep:*s.I Rep -> T) -> T
Implicit 2 unpack

Prove beta_Sig : @I:*s->*s. @T:*s. @Rep:*s. @imp: I Rep. 
                 @m:(@Rep:*s. I Rep -> T).
                     unpack (pack I Rep imp) (\R:*s.\ops:I R. m R ops) = 
                     m Rep imp