[erlang-questions] Variable bindings

Anthony Ramine <>
Sat Jan 26 20:51:24 CET 2013


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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