Difference between Operator and Function in APL?

[firesofmay]

Hi,

I've been reading Mastering Dyalog APL book and I am still not getting the difference between operator and function in APL.

When do you say something is an operator and something is a function in APL?

Thanks!

[Roger|Dyalog]

A function takes array argument(s) and produces an array result; an operator takes array or function argument(s) and usually produces a function, which can then be applied to arrays to produce array results. (Primitive operators always produce a function result.)

Operators are a powerful and useful concept and efficiently connect related concepts. They are closely related to the idea of adverbs in natural languages (and functions related to verbs): run quickly, think quickly, type quickly; run slowly, run efficiently, run haphazardly. If you have n symbols you can use them to define n functions, or n÷2 functions and n÷2 operators and thereby getting (n÷2)+(n*2)÷4 functions. (Even more if the operators are dyadic.)

An operator induces a family of functions: +/, ⌈/, ×/, ∧/, ∨/, etc. Once you've understood how / works on one function (e.g. +/ is summation), you'd have a pretty good handle on how it works on other functions (×/ is product, ⌈/ is maximum, and so on).

[firesofmay]

Thanks Roger for the wonderful explanation.
That helped me in getting the basic difference between the two.