No abstract

Though J shares many concepts with APL, in many respects it is radically different, and almost all APL constructions that are in J differ in some way. These differences can be a stumbling block to the newcomer who thinks that J is simply an ASCII version of APL, prompting questions such as:• How do I save my workspace?• Why do J functions work along the columns and not the rows?• Can I have a version of J with □ io ←1?• Can I have a version of J with real APL characters?

No abstract

Gerunds, verbal forms that can be used as nouns, are recognized as having utility in the realm of programming languages. We show that gerunds can be viewed as arrays of atomic repmentations of verbs (functions), in a way which is consistent with the syntax and semantics of APL, and which allows verbs to be first class objects in the language. We define derivations of verbs from gerunds in the J dialect of APL, and show how these derivations provide control structures for sequencing, selection (in the senseof generalized forms of CASE or SWITCH statements and IF/IYIEN/ELSE), iteration (DO UNTIL), recursion, and parallel computation (MIMD, or Multiple Instruction, NMtiple Data) . We conclude with alternative representations of verbs which are useful in other contexts.

Rank is elucidated through an executable model. Integrated rank support for specific functions can be vastly more efficient than the general algorithm in computing v" r, and uniform verbs provide a way to extend the more efficient implementation to a large class of verbs.