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26 lines
1.1 KiB
Agda
26 lines
1.1 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; _⇒_; _∪_; _∩_; src)
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open import Properties.Subtyping using (dec-subtyping)
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module Luau.OverloadedFunctions where
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-- resolve F V is the result of applying a function of type F
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-- to an argument of type V. This does function overload resolution,
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-- e.g. `resolve (((number) -> string) & ((string) -> number)) (number)` is `string`.
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resolve : Type → Type → Type
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resolve nil V = never
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resolve (S ⇒ T) V = T
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resolve never V = never
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resolve unknown V = unknown
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resolve boolean V = never
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resolve number V = never
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resolve string V = never
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resolve (F ∪ G) V = (resolve F V) ∪ (resolve G V)
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resolve (F ∩ G) V with dec-subtyping V (src F) | dec-subtyping V (src G)
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resolve (F ∩ G) V | Left p | Left q = resolve F V ∪ resolve G V
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resolve (F ∩ G) V | Right p | Left q = resolve F V
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resolve (F ∩ G) V | Left p | Right q = resolve G V
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resolve (F ∩ G) V | Right p | Right q = resolve F V ∩ resolve G V
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