| > * There is provision in C-- for primops that (a) may have more
| > than one result, (b) have effects. This is done by the %% syntax,
| > described at the end of Section 6.3 of the C-- spec.
| > * However this feature is ill-specified by the C-- spec; indeed
| > no %% operators are described at all
|
| I did not understand that reference when I read it the first time.
| Section 6.8.1 mentions 'foreign "C--"', which until now did not make
| sense to me. Now I realise that C-- has a basic runtime system so
| primitive operators must leave the runtime system in order to produce
| side effects. Interesting workaround--reminiscent of mutable
| variables in Haskell. The big question is whether all those extra
| foreign calls may be reduced to the proper assembler mnemonics
| instead of creating special procedures.
Now you've confused me! The form
x = %%op( p, q, r )
has the *form* of a call, and it *may* generate a call, but it also fine for
the C-- compiler to generate a single, inline machine instruction. Indeed that
is what GHC does for the memory-barrier op, I think.
I don't understand your reference to the C-- runtime; it doesn't seem relevant
here.
Simon
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