ucsd-progsys/liquidhaskell

Question about Dependent Sums

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#1,615 opened on Feb 14, 2020

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Description

Hi, I'm trying to represent a function that returns a dependent sum like below

{-@ measure isLeft :: Either a b -> Bool @-}
isLeft (Left _) = True
isLeft (Right _) = False

{-@ example :: x:Int -> {v : Either Int String | (isLeft v && x > 0) || (not (isLeft v) && x <= 0)} @-}
example x =
    if x <= 0 then Right "hello" else Left 1

but am running into issues with liquid. Am I representing this correctly? Even without generics, this still doesn't seem to work in the way I might expect.

Contributor guide

Research direction
Investigate how liquidhaskell processes dependent sum types and the measure isLeft. Trace the type checking path for the given example and identify where the error occurs.
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3
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