Quoting Malcolm Wallace
lennart@augustsson.net writes:
Nhc didn't use to implement the M-R (maybe it does now). When porting code to nhc this caused a few code changes. Perhaps 10 lines out of 10000 when I tried the Bluespec compiler. So my gut feeling is that the M-R is a rare beast in practise.
I can confirm that nhc98 (and hence yhc) still does not implement the M-R. I haven't noticed any particular performance problems in code compiled by nhc98 that were down to a consequent loss of sharing. (But I can't claim to have explicitly looked.) But as Lennart says, you do get occasional type errors which mean you need to restructure your code. Almost always, these are local bindings, e.g.:
Context required in LHS pattern
is an error emitted for code like:
do (x,y) <- something complicated and numeric ...
and the fix is
do xy <- something complicated and numeric let x = fst xy y = snd xy ...
As I recall, there were about 4-5 of these I needed to fix in the entire nofib suite.
The changes I had to make were almost all simpler than that. I just had to add a few type signatures. (And thanks for supporting evidence from nhc. :) -- Lennart