add INLINEABLE to maybe, either, bool

Austin Seipp austin at
Mon Sep 16 22:12:37 CEST 2013

I'm strongly opposed to this.

Being INLINE happy is not a good thing, it is a bad thing. More often
than not, I see people stuffing INLINE all over the place for things
that would trivially be unfolded and put in the interface file anyway.
This is bad, and it teaches people to just use the INLINE hammer
everywhere instead of understanding the actual implications of what
the inliner does. It also makes it impossible to actually observe how
the inliner behaves and see where it needs tuning: if we just mark
everything INLINE, we might as well not have it and make it

There are some particular cases where GHC is hesitant to inline small
things if it would lead to work duplication, or where the inliner
behavior is tweaked and you may want to force it across multiple
versions to be sure (lens is a good example of this.) But this is far
more rare, and this case is not that. In particular, Joachim checked
the 'bool' commit. As expected, the unfolding for bool was put into
the interface file for Data.Bool, meaning if you use -O (or just -O0
-fno-ignore-interface-pragmas,) it should be inlined at call sites
appropriately when it is used.

If we're going to INLINE things, we need to make sure it actually has
an empirical benefit, by looking at the core, and seeing where the
inliner is failing. Not just attach it to things because it seems like
a good idea. This also helps drive feedback into the inliner so we can
see where it fails.

On Mon, Sep 16, 2013 at 2:59 PM, Carter Schonwald
<carter.schonwald at> wrote:
> Its come to my attention that maybe, either, and its new sibling bool, all
> lack the
> INLINEABLE attribute, or its more aggressive sibling INLINE
> this seems like one of those operations where inlining in client use sites
> is a good option to have, and currently not possible!
> theres probably other stuff that would benefit from an INLINEABLE pragma in
> base,
> but this is an obvious, simple, "easy win" that I noticed when Oliver's
> patch got merged into base.
> Thoughts?
> Time scale: sometime this week? (ghc 7.8 merge window is landing!)
> cheers
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> Libraries at

Austin Seipp, Haskell Consultant
Well-Typed LLP,

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