Re: Escapes in Backquoted Strings

Hi

Thank you, this explains a lot. So we have here
a feature (atom_no_escape) and a bug (X = `\`
not accepted).

Bye

Daniel Diaz schrieb:
>   Hello Jan,
>
> sorry for the late reply...
>
> There is a flag to control the meaning of backquoted strings. By default
> it is an atom without interpreting escape sequences.
> But this can be changed (for more info see
> http://gprolog.org/manual/html_node/gprolog045.html#toc178).
>
> Here is an example:
>
> | ?- current_prolog_flag(back_quotes,X).
>
> X = atom_no_escape
>
> yes
> | ?- X=`\x61\`.
>
> X = '\\x61\\'
>
> yes
> | ?- set_prolog_flag(back_quotes,atom).
>
> yes
> | ?- X=`\x61\`.
>
> X = a
>
>
> Hope this helps
>
> Daniel
>
>
> Le 19/03/2011 18:32, Jan Burse a écrit :
>> Dear All
>>
>> I am working with
>>     GNU Prolog 1.3.1
>>     By Daniel Diaz
>>     Copyright (C) 1999-2009 Daniel Diaz
>>
>> It seems that escapes in backquoted strings are
>> detected, but not converted.
>>
>> Normal single quotes:
>>
>>   ?- X = 'abc'.
>>   X = abc
>>   | ?- X = '\''.
>>   X = ''''
>>   ?- X = '\x61\'.
>>   X = a
>>
>> Back quotes:
>>
>>   ?- X = `abc`.
>>   X = abc
>>   ?- X = `\'`.
>>   X = '\\'''
>>   ?- X = `\x61\`.
>>   X = '\\x61\\'
>>
>> It seems that the escapes are not converted. But
>> they are detected during parsing of backquoted
>> strings, at least the first escaped character is
>> always expected:
>>
>>   ?- X = `\`.
>>   .
>>   uncaught exception: error(syntax_error('user_input:10 (char:8)
>>   expression expected or previous operator needs brackets'),read_term/3)
>>
>> But the closing escape character of a noctal or
>> hexadecimal constant seems not to be not expected:
>>
>>   ?- X = `\x61`.
>>   X = '\\x61'.
>>   ?- X = `\0`.
>>   X = '\\0'
>>
>> From my understanding of ISO standard for back quoted strings,
>> the same escaping rules should hold as for single quoted
>> strings. I am referening to non quote char (* 6.4.2.1 *).
>>
>> Is this a bug or a feature?
>>
>> Bye
>>
>>
>>
>>
>>
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