[erlang-questions] The Core Erlang AST via cerl.erl and Sequence returns from functions

[Eric B Merritt]

Robert,

  Thats the same conclusion I came to. I assumed though that an
expression that returned a #c_values would work as well as a direct
#c_values. I actually don't see much use in only supporting only a
direct mapping unless the purpose is solely to allow binding multiple
variables in a single expression. Actually, that may be exactly it. 

Eric

On Mon, 2011-12-26 at 14:14 +0000, Robert Virding wrote:
> I do the same in LFE, compile LFE code down to Core as it is a much simpler language to work with than Erlang. However, I do not use the cerl module but instead use the Core record definitions in core_parse.hrl directly. The code becomes more compact and easier to read. I think. I only have some wrapper functions for very common cases.
> 
> Your example does not work because you have a list of variables in the let which requires that you have a corresponding #c_values{} record as a "value".
> 
> Robert
> 
> ----- Original Message -----
> > Richard,
> > 
> >  Thanks, Its good to know that its not me misunderstanding things. I
> > will see if I can dig into the compiler here in the next couple of
> > days
> > and submit a patch to the patches list.
> > 
> > Eric
> > 
> > On Wed, 2011-12-21 at 21:45 +0100, Richard Carlsson wrote:
> > > On 2011-12-21 17:36, Eric Merritt wrote:
> > > > Guys,
> > > >
> > > > I am currently targeting the Erlang VM for a custom language via
> > > > core
> > > > erlang as defined in cerl.erl on R15B. I have run into an
> > > > interesting
> > > > issue. In a Let form (cerl:c_let) if I have a sequence of c_vars
> > > > on
> > > > the Variable arguement and c_apply (on a function that returns a
> > > > c_values) in the Argument argument then the erlang compiler exits
> > > > with
> > > > an 'error'. However, if I have a c_values directly as the
> > > > Argument
> > > > argument the compiler will compile the form. Either I am
> > > > understanding
> > > > something incorrectly or this is a bug in the cerl compiler. I am
> > > > hoping one of the folks that is knowledgeable on the subject can
> > > > help
> > > > out. In short the following works:
> > > >
> > > >      cerl:c_let([cerl:c_var(x0), cerl:c_var(x1)],
> > > > cerl:c_values([cerl:c_int(0), cerl:c_int(1)]), cerl:c_atom(foo))
> > > >
> > > > while this does not:
> > > >
> > > >      <define a function that returns
> > > >      cerl:c_values([cerl:c_int(0),
> > > > cerl:c_int(1)])>
> > > >
> > > >      cerl:c_let([cerl:c_var(x0), cerl:c_var(x1)],
> > > > cerl:c_apply(cerl:c_fname(my_fun, 0), []), cerl:c_atom(foo)).
> > > 
> > > Intuitively (and without consulting the source code or my old
> > > papers on
> > > Core Erlang), I'd say that the latter should work. However, the OTP
> > > compiler doesn't try to be complete with respect to all possible
> > > Core
> > > Erlang programs - it only bothers to implement what's needed to
> > > handle
> > > code that's first been translated from (full) Erlang. So if you
> > > start
> > > generating arbitrary but legal Core Erlang, you may run into corner
> > > cases (in this case, it seems that multiple return values aren't
> > > handled
> > > as they ought to be). See if you can find the problem in the
> > > compiler -
> > > as Calvin's dad used to say, "it builds character". :-)
> > > 
> > >      /Richard
> > > _______________________________________________
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> > 
> > 
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