1.4.3 not backwards-compatible with code using 1.4.2

[david-christiansen]

Building Idris (both the Hackage release and master) with Trifecta 1.4.3 yields the following error:

[68 of 87] Compiling Idris.ParseHelpers ( src/Idris/ParseHelpers.hs, dist/build/Idris/ParseHelpers.o )

src/Idris/ParseHelpers.hs:370:47:
    No instance for (Show IState) arising from a use of ‘position’
    In the second argument of ‘liftM’, namely ‘position’
    In the expression: liftM ((+ 1) . fromIntegral . column) position
    In an equation for ‘indent’:
        indent = liftM ((+ 1) . fromIntegral . column) position

With Trifecta 1.4.2, this error does not occur.

The change seems to be a result of commit 16cd121. It seems odd that we should be required to have a Show instance for the internal state.

[david-christiansen]

Ah, this seems to be due to ekmett/parsers@fbbac6e

I'll update things accordingly in Idris. But shouldn't extra class constraints give a version bump to at least 1.5, according to the PVP?

[ekmett]

You are correct.

[ekmett]

1.5 shipped. The fact that it needs Show on the state is quite strange I agree. I'll dig into that.

[ekmett]

I've fixed the Show constraints in parsers 0.12.1.

They should no longer be required.