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Erlang tries to evaluate a string

I am trying to dynamically evalutate Erlang members

Erlang launch

basho-catah% erl
Erlang R16B03 (erts-5.10.4) [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]

Eshell V5.10.4  (abort with ^G)

Create a term

1> {a,[b,c,d]}.
{a,[b,c,d]}

Try scanning in the same vein

2> {ok, Tokens, _ } = erl_scan:string("{a,[b,c,d]}").
{ok,[{'{',1},
     {atom,1,a},
     {',',1},
     {'[',1},
     {atom,1,b},
     {',',1},
     {atom,1,c},
     {',',1},
     {atom,1,d},
     {']',1},
     {'}',1}],
    1}


3> Tokens.
[{'{',1},
 {atom,1,a},
 {',',1},
 {'[',1},
 {atom,1,b},
 {',',1},
 {atom,1,c},
 {',',1},
 {atom,1,d},
 {']',1},
 {'}',1}]

But it cannot parse this tokenized string.

4> Foo = erl_parse:parse(Tokens).
{error,{1,erl_parse,["syntax error before: ","'{'"]}}

Any ideas what I am doing wrong?

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1 answer


You are using the wrong function, as well as a caveat you did not encounter.

First, the function you should be using is erl_parse:parse_term/1

. I can't find any documentation for erl_parse:parse/1

, so I suspect it's out of date (and most likely used to parse syntax trees, not tokens).

Second, to work, erl_parse:parse_term/1

you must include the line terminator in your term. erl_scan:string/1

will happily convert whatever you give to tokens, but without a terminator it erl_parse:parse_term/1

expects to get more.



So try this in a shell:

{ok, Tokens, _} = erl_scan:string("{a,[b,c,d]}.").
erl_parse:parse_term(Tokens).
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