[erlang-questions] Bug, feature or limitation of erl_parse?

Robert Virding <>
Tue Aug 24 23:01:16 CEST 2010


Erl_parse does recognise '"test" ++ Else', but it is not a term it is
an expression. It is later inside the compiler that the expression is
converted into it's shortcut form. The parser just parses the
expression. When you did it by hand, so to speak, you got a term which
erl_parse could parse as a term. So:

17> f(S), {ok,S,_} = erl_scan:string("\"test\" ++ Else. ").
{ok,[{string,1,"test"},{'++',1},{var,1,'Else'},{dot,1}],1}
18> erl_parse:parse_exprs(S).
{ok,[{op,1,'++',{string,1,"test"},{var,1,'Else'}}]}

N.B. it it not the string "term" which causes it to be an expression
but the operator '++'.

Robert

On 24 August 2010 22:08, Musumeci, Antonio S
<> wrote:
> It doesn't appear to understand the "test" ++ Else shortcut for [$t,$e,$s,$t|Else]. Reason I noticed was I'm reading in terms as strings and passing them to mnesia:select. erl_parse works fine with [$t|'_'] but not "t" ++ '_'.
>
>> S = "[$t,$e,$s,$t|'_']".
> "[$t,$e,$s,$t|'_']"
>> T = "\"test\" ++ '_'".
> "\"test\" ++ '_'"
>> [$t,$e,$s,$t|'_'] = "test" ++ '_'.
> [116,101,115,116|'_']
>> {ok,S2,_} = erl_scan:string(S).
> {ok,[{'[',1},
>     {char,1,116},
>     {',',1},
>     {char,1,101},
>     {',',1},
>     {char,1,115},
>     {',',1},
>     {char,1,116},
>     {'|',1},
>     {atom,1,'_'},
>     {']',1}],
>    1}
>> {ok,T2,_} = erl_scan:string(T).
> {ok,[{string,1,"test"},{'++',1},{atom,1,'_'}],1}
>> erl_parse:parse_term(S2++[{dot,1}]).
> {ok,[116,101,115,116|'_']}
>> erl_parse:parse_term(T2++[{dot,1}]).
> {error,{1,erl_parse,"bad term"}}
>
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