Matthew Pickering authored May 04, 2017 and Ben Gamari committed May 04, 2017

Previously we would run all the monadic actions and then
combine their results. This caused problems if later actions
raised errors but earlier lookups suceeded. We only want to run later
lookups if the earlier ones fail.

Fixes #13622

Reviewers: RyanGlScott, austin, bgamari, simonpj

Reviewed By: simonpj

Subscribers: simonpj, rwbarton, thomie

GHC Trac Issues: #13622

Differential Revision: https://phabricator.haskell.org/D3515