RE: Meaning of -fno-foldr-build-on?

| So, the fold/build rule is being applied even if you run GHC with
| -fno-foldr-build-on. I RTFSed, and it appears that the only place in
GHC
| where the -ffoldr-build-on command-line option is looked at is in
| DsListComp.lhs.
| 
| In the flag reference in the manual, the effect of -ffoldr-build-on is
listed
| as "Enable foldr-build optimisation" (presumably suggesting that
| -fno-foldr-build-on disables the optimization). This seems misleading
if the
| only thing that -ffoldr-build-on/-fno-foldr-build-on actually does is
to
| control whether list comprehensions are desugared using foldr/build.

It's definitely misleading.  I've removed it, replacing it with a
-frules-off flag to
switch off all rewrite rules.  There's no way to switch off foldr/build
all by itself.

Simon