`declare` should return `nil`

[helins]

Instead of a vector of nil for each declared symbol. It would be best using a loop instead of map for declarations.

[mikera]

Probably should just introduce a Clojure-style for list comprehension macro to do this?

[mikera]

Updated to return nil. Leaving open to consider use of loop in the implementation. for currently uses map under the hood anyway, which perhaps needs changing to loop for more efficiency.