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38 lines
1 KiB
Agda
38 lines
1 KiB
Agda
{-# OPTIONS --rewriting #-}
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open import FFI.Data.Either using (Either; Left; Right)
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open import Luau.Type using (Type; nil; number; string; boolean; never; unknown; _⇒_; _∪_; _∩_)
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open import Luau.TypeNormalization using (normalize)
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module Luau.FunctionTypes where
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-- The domain of a normalized type
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srcⁿ : Type → Type
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srcⁿ (S ⇒ T) = S
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srcⁿ (S ∩ T) = srcⁿ S ∪ srcⁿ T
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srcⁿ never = unknown
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srcⁿ T = never
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-- To get the domain of a type, we normalize it first We need to do
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-- this, since if we try to use it on non-normalized types, we get
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--
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-- src(number ∩ string) = src(number) ∪ src(string) = never ∪ never
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-- src(never) = unknown
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--
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-- so src doesn't respect type equivalence.
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src : Type → Type
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src (S ⇒ T) = S
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src T = srcⁿ(normalize T)
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-- The codomain of a type
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tgt : Type → Type
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tgt nil = never
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tgt (S ⇒ T) = T
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tgt never = never
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tgt unknown = unknown
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tgt number = never
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tgt boolean = never
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tgt string = never
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tgt (S ∪ T) = (tgt S) ∪ (tgt T)
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tgt (S ∩ T) = (tgt S) ∩ (tgt T)
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