Your second `foo` call fails in 1.2 as well. If there was ever a time when it
would have succeeded, it would have been a bug. Since `foo` is a macro, it
receives its arguments unevaluated, so `(str "baz" 34)` will always be received
as a list of three values.
The syntax-quote precondition simply expands into a list containing the symbol
'clojure.core/string? and the value of bar; this is a logically-true value, and
so does not trigger any error.
You want something like:
(defmacro foo
[bar & body]
`(let [bar# ~bar]
(when-not (string? bar#) (IllegalArgumentException. "msg"))
...))
- Chas
On Mar 20, 2012, at 8:34 AM, Shantanu Kumar wrote:
> Hi,
>
> The way preconditions are invoked in Clojure 1.3.0 seems to have
> changed since Clojure 1.2:
>
> (defmacro foo
> [bar & body]
> {:pre [(string? bar)]}
> ...)
>
> (foo "bar34" ...) ; doesn't complain, which is OK
> (foo (str "baz" 34) ...) ; Error! (I wanted this to pass)
>
> When I write the precondition like this:
>
> {:pre [`(string? ~bar)]}
>
> It doesn't seem to check the precondition at all in 1.3.0.
>
> Can somebody suggest me what am I missing? I want both the examples
> above to be verified and passed as OK.
>
> Shantanu
>
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