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<  Erlang  ~  Extracting Erlang datatypes from strings
anderst
Posted: Sun Jul 29, 2007 2:41 pm Reply with quote
User Joined: 21 Nov 2006 Posts: 37
Hi,

I using jabber as a protocol to push information to (potentially) 100,000+ users. The clients send back information on their environment as Erlang datatypes. These datatypes are received as a binary. eg:
Code:
<<"[foo,{bar,baz, [1,2,3,4]}]">>


I want to transform this binary to an Erlang datatype with as little code as possible. Performance is not an issue. What I would be inclined to do is

Code:
8> B = binary_to_list( <<"[foo,{bar,baz, [1,2,3,4]}]">>).
"[foo,{bar,baz, [1,2,3,4]}]"
9> erl_scan:string(B).                                   
{ok,[{'[',1},
     {atom,1,foo},
     {',',1},
     {'{',1},
     {atom,1,bar},
     {',',1},
     {atom,1,baz},
     {',',1},
     {'[',1},
     {integer,1,1},
     {',',1},
     {integer,1,2},
     {',',1},
     {integer,1,3},
     {',',1},
     {integer,1,4},
     {']',1},
     {'}',1},
     {']',1}],
    1}


What next? Is there a function I could use to create the Erlang datastructure? I could not find one in the documentation.

Hilsen,
Anders[/code]
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arcatan
Posted: Sun Jul 29, 2007 6:54 pm Reply with quote
Joined: 19 Jul 2007 Posts: 2 Location: Finland
I don't know if this is the simplest way, but to continue, you could use erl_parse:parse_term. Note that you have to add a dot to the end of the term to make it complete:

Code:

2> B = binary_to_list( <<"[foo,{bar,baz, [1,2,3,4]}].">>).   
"[foo,{bar,baz, [1,2,3,4]}]."
3> {ok, Tokens, _} = erl_scan:string(B).
{ok,[{'[',1},
     {atom,1,foo},
     {',',1},
     {'{',1},
     {atom,1,bar},
     {',',1},
     {atom,1,baz},
     {',',1},
     {'[',1},
     {integer,1,1},
     {',',1},
     {integer,1,2},
     {',',1},
     {integer,1,3},
     {',',1},
     {integer,1,4},
     {']',1},
     {'}',1},
     {']',1},
     {dot,1}],
    1}
4> erl_parse:parse_term(Tokens).
{ok,[foo,{bar,baz,[1,2,3,4]}]}
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alexaandru
Posted: Mon Jul 30, 2007 7:56 am Reply with quote
Benchmarking Hobbist Joined: 19 Jun 2007 Posts: 18 Location: Oradea, Romania
Hi all,

Here's a page from the CookBook -> StringRecipes that may also help you: http://www.trapexit.org/index.php/String_Eval

Good luck,
Alex
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anderst
Posted: Mon Jul 30, 2007 9:05 am Reply with quote
User Joined: 21 Nov 2006 Posts: 37
Under my very nose on trapexit! Thank you all for the quick reply.

Hilsen,
Anders
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datacompboy
Posted: Thu Aug 30, 2007 5:00 am Reply with quote
User Joined: 21 Sep 2006 Posts: 69 Location: Novosibirsk, Russia
may be better use term_to_binary(X) on sending side, you got binary represention of any term.
on receiver side just do binary_to_term :)

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anderst
Posted: Sun Sep 09, 2007 6:16 pm Reply with quote
User Joined: 21 Nov 2006 Posts: 37
Good idea. Unfortunately, the client is lightweight and written in something more appropriate (J**a).

Hilsen,
Anders
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