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

Robert Virding <>
Mon Dec 26 15:14:16 CET 2011


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
> > _______________________________________________
> > erlang-questions mailing list
> > 
> > http://erlang.org/mailman/listinfo/erlang-questions
> 
> 
> _______________________________________________
> erlang-questions mailing list
> 
> http://erlang.org/mailman/listinfo/erlang-questions
> 



More information about the erlang-questions mailing list