by Davin Church » October 16th, 2018, 3:12 pm
Nope - I mean like the difference between Each and Rho. Rho is a "function" - it takes data on one or both sides and returns data. Each is an "operator" - it takes a function (such as Rho) as an operand and thus creates a "Rho-Each" derived function, which can then be applied monadically or dyadically to (nested) data to return (nested) data. Each, by itself, cannot do anything to data (e.g. can you say "3¨4"?); it only applies to functions to modify them (technically, to be modified BY them).
APL+Win has few true operators. APL2, for example, has a few more and Dyalog has a number of them. Also, APL2 and Dyalog (among other systems) allow you to code your own user-defined operators in much the same way as you code user-defined functions (which I'd really like to be able to do in APL64).
In most other languages, they've taken to calling mathematical symbols "operators" and user-created code "functions", but that's not their correct definitions. APL has it right.