cabal install does not upgrade cabal

问题

I have upgraded cabal install (using a capital C for Cabal)

$cabal install Cabal cabal-install

[...]

Configuring cabal-install-1.24.0.2...
Building cabal-install-1.24.0.2...
Installed cabal-install-1.24.0.2

after a lengthy output in terminal, then I check that cabal has been updated, it hasn't changed

$ cabal --version
cabal-install version 1.22.6.0
using version 1.22.5.0 of the Cabal library

I am looking for where the new installation of cabal might be

$ which cabal
/usr/local/bin/cabal

$ /usr/local/bin/cabal --version
cabal-install version 1.24.0.2
compiled using version 1.24.2.0 of the Cabal library 

Not entirely sure what I have found.

来源：https://stackoverflow.com/questions/42321540/cabal-install-does-not-upgrade-cabal