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Parse error in measure definition #2408

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amigalemming opened this issue Oct 24, 2024 · 0 comments

amigalemming commented Oct 24, 2024

I try to replicate measure definitions as in https://github.com/ucsd-progsys/liquidhaskell/blob/develop/tests/pos/Class2.hs .

{-@ class measure sz :: forall a. a -> Int  @-}
{-@ instance measure sz :: () -> Int
        sz () = 1
  @-}
{-@ instance measure sz :: Int -> Int
        sz n = n
  @-}

LiquidHaskell says:

src/Example/Size.hs:5:13: error:
    Cannot parse specification:
    unexpected ')'
    expecting '[', '_', dataConNameP, or lowercase letter
  |
5 |         sz () = 1
  |             ^

src/Example/Size.hs:8:12: error:
    Cannot parse specification:
    unexpected 'n'
    expecting measurePatP
  |
8 |         sz n = n
  |            ^

The examples define measures on user defined ADTs only. Are measures restricted to those?

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