[erlang-questions] Variable bindings

Steve Vinoski <>
Sat Jan 26 21:06:41 CET 2013


Hi Anthony, thanks for letting me know -- I'll need to try that. I've never
played with erl_syntax_lib before.

I also realized the current version doesn't handle nested anonymous
functions, so I'll need to fix that too.

--steve

On Sat, Jan 26, 2013 at 2:51 PM, Anthony Ramine <> wrote:

> Hi,
>
> An easier way to write this parse transform would be to populate the AST
> with its bindings with erl_syntax_lib:annotate_bindings/2 and then to
> fold through the tree with erl_syntax_lib:fold/3 to replace local calls
> to get_all_bindings/1.
>
> Regards,
>
> --
> Anthony Ramine
>
> Le 26 janv. 2013 à 19:45, Steve Vinoski a écrit :
>
> >
> >
> > On Sat, Jan 26, 2013 at 9:32 AM, Tyron Zerafa <>
> wrote:
> > Does there exist any particular function which would give me all
> variable bindings (including their values) at that point. For instance,
> something similar to get_all_bindings (example below) should result in
> [{X=3},{Y=4}] when called with X=2.
> >
> > my_fun(X) ->
> >     Y = X+1,
> >      get_all_bindings().
> >
> > I don't think anything like that exists, but here's a parse transform
> that might work for you:
> >
> > https://gist.github.com/4643721
> >
> > The parse transform looks for a call to get_all_bindings/1 in each
> function body and replaces its argument with a list of variable names and
> their bindings used in the function up to that point. The argument to
> get_all_bindings can be anything because the parse transform replaces it.
> Example:
> >
> > -module(foo).
> > -export([my_fun/1]).
> > -compile([{parse_transform,get_all_bindings}]).
> >
> > -record(rec, {f1, f2, f3}).
> >
> > my_fun(X) ->
> >     Y = X+1,
> >     Z = [a,b,c,d,e,{X,Y}],
> >     #rec{f1=F1, f2=F2, f3=F3} = #rec{f1=42, f2=[X,Y], f3=Z},
> >     get_all_bindings([]),
> >     Q = 32,
> >     Q.
> >
> > get_all_bindings(Bindings) ->
> >     io:format("~p~n", [Bindings]).
> >
> > The code produced for my_fun/1 by the parse transform looks like this:
> >
> > my_fun(X) ->
> >     Y = X + 1,
> >     Z = [a, b, c, d, e, {X, Y}],
> >     #rec{f1 = F1, f2 = F2, f3 = F3} = #rec{f1 = 42,
> >                                            f2 = [X, Y], f3 = Z},
> >     get_all_bindings([{'Z', Z}, {'Y', Y}, {'X', X},
> >                       {'F3', F3}, {'F2', F2}, {'F1', F1}]),
> >     Q = 32,
> >     Q.
> >
> > Note that Q isn't included in the list because it occurs after the call
> to get_all_bindings/1.
> >
> > --steve
> >
> >
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> > 
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>
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