Question

While trying to install Reactive with cabal, I get this:

src/FRP/Reactive/PrimReactive.hs:79:8:
    Could not find module `Control.Comonad'
    It is a member of the hidden package `comonad-1.1.1.6'.
    Perhaps you need to add `comonad' to the build-depends in your .cabal file.
    It is a member of the hidden package `comonad-3.0.0.1'.
    Perhaps you need to add `comonad' to the build-depends in your .cabal file.

According to this, it indeed has no comonad dependency. However, it uses Control.Comonad in PrimReactive.hs.

Answer 1

The problem is that it depends on category-extras >=0.53.5, but has no upper bound. The category-extras package was recently deprecated (in favor of a less monolithic collection of packages), and a meta-package with information about where modules and functionality ended up was uploaded in its place.

Either give an upper bound like this:

cabal install reactive --constraint "category-extras < 0.54"

or change the cabal file to depend on the appropriate split-up packages instead. The latter is likely to be much more work (especially since many interfaces significantly changed in the split).