On 2010 Apr 22, at 8:17 AM, Base wrote:
say i have a string that contains a form:
"(+ 1 1)"
I want to actually execute this. How do you do this? I thought that
eval would be able to handle this but apparently am misunderstanding
what eval does.
Well, eval is the second half of what you want.
eval evaluates a form.
user=> (read-string "(+ 1 1)")
(+ 1 1)
user=> (eval (read-string "(+ 1 1)"))
2
eval can be a dangerous thing to use, you have to be very careful
about where the source has come from, in terms of trusting that the
code your programs 'eval's will not be malicious or dangerous in some
way. There are no absolute rules for this, it depends on your
application.
read can also be a dangerous thing to use, as per the doc on *read-
eval* quoted here:
clojure.core/*read-eval*
nil
When set to logical false, the EvalReader (#=(...)) is disabled in
the
read/load in the thread-local binding.
Example: (binding [*read-eval* false] (read-string "#=(eval (def x
3))"))
Defaults to true
(Note to doc folks, #= does not seem to be described on: http://clojure.org/reader
with the other # reader macros.)
-Doug
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