The problem is: how do you tell the difference between a pre- and
post-condition map, and a map you want to return from the function?
The only way to do it is to explicitly return nil.
- James
On 15 February 2016 at 04:48, Laws <smashcompan...@gmail.com> wrote:
> If I write this in a file:
>
> (defn different-order [order]
> {:pre [
> (map? order)
> (:waiter order)
> (:customer order)
> (:menu-item-name order)
> ]
> :post [
> (map? %)
> (:waiter %)
> (:customer %)
> (:menu-item-name %)
> ]}
>
> )
>
> and then I try "lein uberjar" I get:
>
> Exception in thread "main" java.lang.RuntimeException: Unable to resolve
> symbol: % in this context
>
> but if I add a line of code to the function body:
>
> (defn different-order [order]
> {:pre [
> (map? order)
> (:waiter order)
> (:customer order)
> (:menu-item-name order)
> ]
> :post [
> (map? %)
> (:waiter %)
> (:customer %)
> (:menu-item-name %)
> ]}
>
> (println "hi")
>
> )
>
> Then it compiles.
>
> At the very least, we should have a better error message than "Unable to
> resolve symbol: % in this context". Something like "function definition is
> incomplete" would at least communicate what the problem is.
>
> But if this really needs to be treated as an error, I would like to know
> why it needs to be an error. This does not generate an error:
>
> (defn different-order [order] )
>
> So why does adding a :post assertion create a compile time error? I'd
> expect a runtime error, but not a compile time error.
>
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