Haskell timeit Module - SystemTimeIT not found - haskell

Question

This must be very simple; but why this error:
PS C:\Users\guthrie\Desktop> cabal install --lib timeit
Resolving dependencies...
Up to date
PS C:\Users\guthrie\Desktop> ghci
GHCi, version 8.10.2: https://www.haskell.org/ghc/ :? for help
Prelude> :m System.TimeIt
<no location info>: error:
Could not find module `System.TimeIt'
Perhaps you meant System.Timeout (from base-4.14.1.0)
Prelude>
Leaving GHCi.
Hackage shows System.TimeIt as being defined in timeit-2.0, which is what cabal installed.
PS C:\Users\guthrie\Desktop> cabal install timeit
Resolving dependencies...
Build profile: -w ghc-8.10.2 -O1
In order, the following will be built (use -v for more details):
- timeit-2.0 (lib) (requires download & build)
Downloading timeit-2.0
Downloaded timeit-2.0
Starting timeit-2.0 (lib)
Building timeit-2.0 (lib)
Installing timeit-2.0 (lib)
Completed timeit-2.0 (lib)
Checking again:
PS C:\Users\guthrie\Desktop> cabal install --lib timeit
Resolving dependencies...
Up to date
But trying to check on it from cabal info::
PS C:\Users\guthrie\Desktop> cabal info timeit
* timeit (library)
Synopsis: Time monadic computations with an IO base.
Versions available: 0.9.0.0, 1.0.0.0, 2.0
Versions installed: [ Not installed ]
Homepage: https://github.com/merijn/timeit
Bug reports: https://github.com/merijn/timeit/issues
Description: A simple wrapper to show the used CPU time of monadic
computation with an IO base.
Category: System
License: BSD3
Author: Lennart Augustsson
Maintainer: Merijn Verstraaten <merijn#inconsistent.nl>, Lennart Augustsson
Source repo: ssh://github.com:merijn/timeit.git
Dependencies: base >=3 && <5, transformers >=0.2 && <0.6
Cached: Yes
Modules:
System.TimeIt
So it reports: "Not installed".
Same problem with criterion (Criterion.Main).
I see a note from 2/2020; that if a package is installed without the --lib option,
It does add the library to the package db in this case but does not
add it to the default environment.
(*https://github.com/haskell/cabal/issues/6262#issuecomment-589843722)
So I repeated the install with this option, no effect - just reported "Up to date".
That same link gave a solution (work-around?) to use instead cabal v1-install, which does work. But what would be the recommended simple solution to be able just to use ghci for testing small codes? Forced migration to stack, with local sandboxed and copies of everything for every small test?
Since I am only doing very simple short tests of examples, I was not creating a sandbox for each, and do not have a .cabal file, are those now necessary?!
(cabal 3.2.0.o, ghc 8.10.2, Windows 10)

Answer 1

I strongly recommend that you don't try to use ghc and ghci directly but instead use cabal. If you want to quickly play around with timeit in the REPL then use
cabal v2-repl --build-depends timeit
If you want to do anything more complicated then create a (perhaps temporary) project and add timeit as a dependency:
$ mkdir my-temporary-package
$ cd my-temporary-package
$ cabal init
Edit my-temporary-package.cabal to change
build-depends: base >=... && <...
to
build-depends: base, timeit
(The constraints on base are going to cause you more harm than good for a quick exploratory project. You can add them back later if it becomes necessary.) Then
$ cabal v2-repl
will get you a REPL with timeit available.