Re: [Caml-list] recursive modules redux, & interface files

[Fergus Henderson <fjh@cs.mu.OZ.AU>]

On 23-Mar-2001, Brian Rogoff <bpr@best.com> wrote:
> On Sat, 24 Mar 2001, Fergus Henderson wrote:
> > 
> > In the Mercury compiler, we have made significant use of module spanning
> > mutually recursive procedures.  For example, the code generator
> > is split among several modules, roughly for each language construct
> > (e.g. ite_gen handles code generation for if-then-elses,
> > switch_gen handles code generation for switches, etc.),
> > and since if-then-elses can contain switches (and vice versa),
> > the procedures in these modules are mutually recursive.
> 
> Interesting. A similar example occurred in a discussion in comp.lang.ml 
> between Matthias Blume and Greg Morrissett (concerning datatypes not
> functions) where MB argued as an SML/NJ maintainer that such recurrences
> were best placed in the same module and GM thought it best that they be
> split even though recursive. Clearly I lean towards MB's view on this 
> though I take it that there are other schools of thought. 
> 
> What is your criteria for splitting the functions into different modules?

Our criteria are pretty informal: each module should consist of closely
related code, preferably with a single purpose that can be summed up
in a concise title, e.g. "code generation for if-then-elses".

In this case, I think the code was originally in a single module,
but was split into sub-modules when it became too large.
Here's the line counts of the relevant modules:

       768 call_gen.m
      1296 code_gen.m
        67 commit_gen.m
       324 disj_gen.m
       360 ite_gen.m
       283 par_conj_gen.m
      1254 pragma_c_gen.m
       313 switch_gen.m
       897 unify_gen.m
       245 dense_switch.m
       549 lookup_switch.m
       246 string_switch.m
      1100 tag_switch.m
       584 middle_rec.m
      ----
      8286

Generally we prefer to make modules in the range of about 200-2000
lines of code each.  If a module gets much larger than that, then
it tends to get a bit unwieldy, and recompilation times start to become
inconvenient, so we prefer to split up modules that get larger than that.
8000 lines is definitely way too big.

-- 
Fergus Henderson <fjh@cs.mu.oz.au>  |  "I have always known that the pursuit
                                    |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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