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Php and macros (lisp style)?

Hi I was learning LISP and well, all day I was programming php for life, so I fiddled with php.net and found the eval function ... so I started playing!

I would love to know more about how to use eval to do crazy things, I know you can do functions with this and all ... but I wanted to ask why the following code won't work:

$var = "echo \"FOZZ\";";
for($i = 0; $i < 100; $i++)
    $var  = "eval(\"".$var."\");";
print $var;   
eval($var);

And what's even more interesting with eval!

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3 answers


Your statement goes out to "eval (" eval "(" echo "FOZZ"; ");"). Your double quotes interfere with each other and cause an error.

You can try changing the first line to $ var = "echo \" FOZZ \ '; ";



Note. Be careful with using eval.

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For the common web programming case, Ive developed a library called xilla_tags that makes it easier to write lisp-flavored PHP code that can be much more readable than the traditional approach.

For xilla_tags see the xilla tag sample .



Regarding the lisp style in PHP, Jacob Hannsen has a great article on his bitch website for a more general case.

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It won't work because you need to escape the quotes inside the quoted string. Since it $var

contains quotes, you need to escape the quotes on each iteration by stuffing it in a different eval layer.

Despite this, I do not tolerate overuse eval()

. Using it even once should be rare and only done when absolutely necessary. eval()

in any programming language there is an accident waiting to exist.

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