Proposal: NoImplicitPreludeImport

Bryan O'Sullivan bos at
Tue May 28 18:07:57 CEST 2013

On Tue, May 28, 2013 at 8:23 AM, Ian Lynagh <ian at> wrote:

> I have made a wiki page describing a new proposal,
> NoImplicitPreludeImport, which I intend to propose for Haskell 2014:
> What do you think?

This is a truly terrible idea.

It purports to be a step towards fixing the backwards compatibility
problem, but of course it breaks every module ever written along the way,
and it means that packages that try to be compatible across multiple
versions of GHC will need mandatory CPP #ifdefs for years to come.

The current model that we have, of opting out of the Prelude explicitly,
provides the same capability without damning the entire Haskell world to a
months-long edit-recompile cycle.

Of course being able to evolve the language and its libraries is important,
but experience from other languages (e.g. Python, Ruby) offer the lesson
that ignoring the "if it ain't broke, don't fix it" rule is very perilous:
it risks hobbling language growth and development for years. This proposal
takes that rule and maximally flouts it, while offering scant payoff in
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