9. Frequently Asked Questions¶
Joxa is a very small functional language. Its actually designed less to be a language as a tool set in which to build domain specific languages through the use of macros and libraries.
Though it is based on the Erlang VM it is not, and has no intention of being, Erlang.
9.1. What is the difference between Joxa and LFE (both Lisps for the Erlang VM)¶
This is best explained in the following post: http://ericbmerritt.posterous.com/differences-between-joxa-and-lfe
9.2. How Do You Create Mutually Recursive Functions¶
All functions in Joxa have to be declared before they can be used. For recursive functions this works fine, however, for two functions that recurse on each other there doesn’t seem to be much you can do.
9.3. Type Specs are your answer¶
Do a defspec of the function before using it. Specs, aside from providing type information to the compiler, also serve as a pre-declaration. For example, lets say you had this function:
(defn even? (number) (case number (0 :true) (_ (odd? (- (erlang/abs number) 1))))) (defn odd? (number) (case number (0 :false) (_ (even? (- (erlang/abs number) 1)))))
This obviously wont work because odd? will not be declared when even? is defined. You can get around this problem by declaring a defspec for odd?.
(defspec odd? ((erlang/integer)) (erlang/boolean)) (defn even? (number) (case number (0 :true) (_ (odd? (- (erlang/abs number) 1))))) (defn odd? (number) (case number (0 :false) (_ (even? (- (erlang/abs number) 1)))))
With this it works because you have declared your intent to implement odd? on which even? depends.
9.4. Will compiler.jxa ever be able to use macros?¶
Probably not, its a problem in the erts code loading scheme. Macros take iterative compilation that is, each form needs to be available at compile time so you have to compile each form and load it individually. When you load the compiler, it overrides the joxa.compiler module currently loaded and since the new thing is incomplete it breaks.
I think there might be some possibility using of the new/old positions in the code loader but that is a long shot. So for the compiler, and the compiler only, macros are not usable. Thats why the bootstrap flag is there it aborts iterative compilation and just does it all in one fell swoop.