I need a mini "logic interpreter"

[Baron Samedi]

I want to extend the PHP based blog system which I use.

We have static templates for the various blog pages and I would like to
introduce some logic to them.

That is, I want to have some sort of structure, like

[[if <condition>]]
[[else]]
[[endif]]

or [[for 0, 3]] // do 4 time
[[endfor]]

but I am bogged down at the very first hurdle, which is just evaluating
something like '2 == 2.".

The text from the templates will be seen as a string, of course, but
when I try to evaluate it as a bool,
echo 'Evaluated condition: "' . (bool) $text . '"<br>';

it always evaluates to true, even if my condition is '2 == 3'.

Obviously I am missing something very basic about evaluation and maybe
casting.

Can anyone enlighten me, please?

[Alan Little]

Re: I need a mini &quot;logic interpreter&quo t;

Carved in mystic runes upon the very living rock, the last words of Baron
Samedi of comp.lang.php make plain:
[color=blue]
> I want to extend the PHP based blog system which I use.
>
> We have static templates for the various blog pages and I would like to
> introduce some logic to them.
>
> That is, I want to have some sort of structure, like
>
> [[if <condition>]]
> [[else]]
> [[endif]]
>
> or [[for 0, 3]] // do 4 time
> [[endfor]]
>
> but I am bogged down at the very first hurdle, which is just evaluating
> something like '2 == 2.".
>
> The text from the templates will be seen as a string, of course, but
> when I try to evaluate it as a bool,
> echo 'Evaluated condition: "' . (bool) $text . '"<br>';
>
> it always evaluates to true, even if my condition is '2 == 3'.[/color]

Strings and non-zero numbers evaluate to TRUE. You might consider the
eval() function.

eval('$conditio n = ($text)? true : false;');

if ($condtion) {
}

The usual caveats about not trusting visitor input apply.

I have a template processor I've been developing, that might work for
you. It's kind of a work-in-progress, but I've used it in production
environments. Email me if you'd like a copy.

--
Alan Little
Phorm PHP Form Processor

http://www.phorm.com/

[Baron Samedi]

Re: I need a mini &quot;logic interpreter&quo t;

$text = '2==2';

eval('$conditio n = ($text)? true : false;');

if ($condtion)
echo '<hr>True<hr>' ;
else
echo '<hr>False<hr>' ;


--------------------------------------------------------------------------------
False
--------------------------------------------------------------------------------

[Alan Little]

Re: I need a mini &quot;logic interpreter&quo t;

Carved in mystic runes upon the very living rock, the last words of
Baron Samedi of comp.lang.php make plain:
[color=blue]
> $text = '2==2';
>
> eval('$conditio n = ($text)? true : false;');
>
> if ($condtion)
> echo '<hr>True<hr>' ;
> else
> echo '<hr>False<hr>' ;
>
>
> -----------------------------------------------------------------------
> False
> -----------------------------------------------------------------------[/color]

1) Variables in single quotes do not get evaluated. That expression
needs to be in double quotes, and then you need to escape the $
for $condition

2) You have a typo. You have $condition in your eval, and $condtion
in your if().

--
Alan Little
Phorm PHP Form Processor

http://www.phorm.com/

[Baron Samedi]

Re: I need a mini &quot;logic interpreter&quo t;

1) oops, I didn't know that about the single quotes. Thanks.

What did you mean by "escape the $ for $condition " ?

2) thanks for that.

it is still not working ("2==3" gicves true) , so I guess that I need
to "escape the $ in $condition".

Thanks for your help.

[Rik]

Re: I need a mini &quot;logic interpreter&quo t;

Baron Samedi wrote:[color=blue]
> 1) oops, I didn't know that about the single quotes. Thanks.
>
> What did you mean by "escape the $ for $condition " ?[/color]

In:
eval("$conditio n = ($text)? true : false;");

PHP will try to search for the variable "condition" to put in the eval
statement.

Escaping it like:
eval("\$conditi on = ($text)? true : false;");

will let PHP know it has to treat this part as text, so it will be evalled
as "$condition " and not the value of the (prehaps existing) variable
$condition. If it tries to replace it with the value of the variables
"condition" , there is off course no way $condition gets set in this
statement.

Grtz,
--
Rik Wasmus

[Jerry Stuckle]

Re: I need a mini &quot;logic interpreter&quo t;

Rik wrote:[color=blue]
> Baron Samedi wrote:
>[color=green]
>>1) oops, I didn't know that about the single quotes. Thanks.
>>
>>What did you mean by "escape the $ for $condition " ?[/color]
>
>
> In:
> eval("$conditio n = ($text)? true : false;");
>
> PHP will try to search for the variable "condition" to put in the eval
> statement.
>
> Escaping it like:
> eval("\$conditi on = ($text)? true : false;");
>
> will let PHP know it has to treat this part as text, so it will be evalled
> as "$condition " and not the value of the (prehaps existing) variable
> $condition. If it tries to replace it with the value of the variables
> "condition" , there is off course no way $condition gets set in this
> statement.
>
> Grtz,[/color]

How about:

$condition = (eval ($text)) ? true : false;

--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attgl obal.net
=============== ===

[Alan Little]

Re: I need a mini &quot;logic interpreter&quo t;

Carved in mystic runes upon the very living rock, the last words of
Jerry Stuckle of comp.lang.php make plain:
[color=blue]
> Rik wrote:[color=green]
>> Baron Samedi wrote:
>>[color=darkred]
>>>1) oops, I didn't know that about the single quotes. Thanks.
>>>
>>>What did you mean by "escape the $ for $condition " ?[/color]
>>
>> In:
>> eval("$conditio n = ($text)? true : false;");
>>
>> PHP will try to search for the variable "condition" to put in the
>> eval statement.
>>
>> Escaping it like:
>> eval("\$conditi on = ($text)? true : false;");
>>
>> will let PHP know it has to treat this part as text[/color]
>
> How about:
>
> $condition = (eval ($text)) ? true : false;[/color]

That gives a parse error in the eval, as 2==3 is not a syntactically
valid PHP statement.

--
Alan Little
Phorm PHP Form Processor

http://www.phorm.com/

[Baron Samedi]

Re: I need a mini &quot;logic interpreter&quo t;

Isn't it a condition? Do I have to wrap it in brackets? Nope, taht
doesn't work.

Of course "(2==3")" is just an example. The problem is taht I don't
knwo what users will code ther. Could be anything, so long as it is a
condition.

Can you help me out with a code example? I would be very grateful.

[Baron Samedi]

Re: I need a mini &quot;logic interpreter&quo t;

$text = "(2==3)";

eval('\$conditi on = ($text)? true : false;');


Warning: Unexpected character in input: '\' (ASCII=92) state=1 in
C:\graham\blog\ extensions\_sni ppet_dev\~scp.p hp(127) : eval()'d code on
line 1

Sorry, I still don't get it to work.

[Alan Little]

Re: I need a mini &quot;logic interpreter&quo t;

Carved in mystic runes upon the very living rock, the last words of Baron
Samedi of comp.lang.php make plain:
[color=blue]
> $text = "(2==3)";[/color]

No parentheses.
[color=blue]
> eval('\$conditi on = ($text)? true : false;');[/color]

Double qoutes, man. Double quotes.
[color=blue]
> Warning: Unexpected character in input: '\' (ASCII=92) state=1 in
> C:\graham\blog\ extensions\_sni ppet_dev\~scp.p hp(127) : eval()'d code on
> line 1
>
> Sorry, I still don't get it to work.[/color]


--
Alan Little
Phorm PHP Form Processor

http://www.phorm.com/

[Rik]

Re: I need a mini &quot;logic interpreter&quo t;

Baron Samedi wrote:[color=blue]
> $text = "(2==3)";
>
> eval('\$conditi on = ($text)? true : false;');
>
>
> Warning: Unexpected character in input: '\' (ASCII=92) state=1 in
> C:\graham\blog\ extensions\_sni ppet_dev\~scp.p hp(127) : eval()'d code
> on line 1[/color]

eval("\$conditi on = ($text)? true : false;"); or
eval('$conditio n = ('.$text.')? true : false;');

Grtz,
--
Rik Wasmus

[Rik]

Re: I need a mini &quot;logic interpreter&quo t;

Alan Little wrote:[color=blue]
> Carved in mystic runes upon the very living rock, the last words of
> Baron Samedi of comp.lang.php make plain:
>[color=green]
>> $text = "(2==3)";[/color]
>
> No parentheses.
>[color=green]
>> eval('\$conditi on = ($text)? true : false;');[/color]
>
> Double qoutes, man. Double quotes.[/color]

Yup,
eval("\$conditi on = ($text)? true : false;");
or
eval('$conditio n = ('.$text.')? true : false;');

For quoting-education:

http://nl2.php.net/manual/en/language.types.string.php

Grtz,
--
Rik Wasmus

[the DtTvB]

Re: I need a mini &quot;logic interpreter&quo t;

I made one

Source file: http://dttvb.yi.org/tparser.phps
There are still some problems about nesting. But it works quite well.

-- TESTS --
echo dtsparse('[[if 2==2]]this condition is true[[else]]this condition
is false[[endif]]');
// Outputs this condition is true
echo dtsparse('[[if 3==2]]this condition is true[[else]]this condition
is false[[endif]]');
// Outputs this condition is false
echo dtsparse('[[if 3>2]]this condition is true[[else]]this condition
is false[[endif]]');
// Outputs this condition is true
echo dtsparse('befor e if[[if 3==3]], this condition is true[[endif]],
after if');
// Outputs before if, this condition is true, after if
echo dtsparse('befor e if[[if 3==2]], this condition is true[[endif]],
after if');
// Outputs before if, after if
echo dtsparse('[[for 5,10]]aa [[endfor]]');
// Outputs aa aa aa aa aa aa
echo dtsparse('[[for 5 to 10]][[index]],[[endfor]]finish');
// Outputs 5,6,7,8,9,10,fi nish

Is that what you want? Sorry if it's not.

[Baron Samedi]

Re: I need a mini &quot;logic interpreter&quo t;

This looks ecxcellent!! Is it GPL? If s, can you please mail me the
code & test script?

Thank you very much for your help!