I've a database which returns vaild CL expressions within double quotes.
Is it possible to convert these strings to expressions.
For example, I make a query from this DB via CLSQL and as a result it returns me:
"(foo a b)"
How should I convert this expression to:
(foo a b)
and further evaluate it?
> (read-from-string "(foo a b)")
(FOO A B) ;
9
The 9 is the second of multiple values produced by read-from-string; you can ignore it:
(eval (read-from-string "(foo a b)"))
will do what you want given the proper definitions.
* (read-from-string "(+ 1 2)")
(+ 1 2)
7
There is a security problem. See the variable *read-eval*.
* (read-from-string "#.(+ 1 2)")
3
9
You really need to make sure that *read-eval* is NIL, so that reading will not evaluate code.
* (let ((*read-eval* nil)) (read-from-string "#.(+ 1 2)"))
debugger invoked on a SB-INT:SIMPLE-READER-ERROR:
can't read #. while *READ-EVAL* is NIL
Additionally calling EVAL on arbitrary input from a database is not a good idea.
Usually you want to make sure that the code does only call allowed functions.
