The dreaded M-R

Sebastian Sylvan sebastian.sylvan at
Mon Jan 30 12:00:14 EST 2006

On 1/30/06, Simon Marlow <simonmar at> wrote:
> I've put a wiki page with a summary of this discussion here:
> ismRestriction
> Hopefully I've captured most of the important points, please let me know
> if there's anything I missed, or misrepresented.  I'll add a ticket
> shortly.
> Given the new evidence that it's actually rather hard to demonstrate any
> performance loss in the absence of the M-R with GHC, I'm attracted to
> the option of removing it in favour of a warning.

Given that the discussion has focused a lot on how beginners would
feel about this, I'll chime in with my two cents. I may not be a
beginner in the strictest sense of the word, but I'm probably a lot
closer to it than the rest of the participants in this discussion :-)

I'm against it. People will want to *understand* the difference
between ":=" and "=", and I don't think beginners will really grok
something like that without significant difficulties. And it does add
a significant extra clutter to the language, IMO. That symbols feels
"heavy", somehow, even if it's meaning is subtle (at least from a
beginners POV).

Also, since it's only a problem very rarely, it could be noted in an
"optimization faq" somewhere. Plus, don't we already tell people to
add type signatures when something is too slow? Isn't that the first
thing you would try when something is surprisingly slow?


Sebastian Sylvan
UIN: 44640862

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