Functional REXX

A set of procedures that implement the basics of functional programming – as in languages like LISP and Haskell – in non-object-oriented REXX.

In particular, it provides the following features:

• Anonymous, first-class functions (called using a special ? procedure)
  • Basically, procedures can be stored in variables
  • This allows for higher-order procedures: procedures whose arguments or return values are themselves procedures
• Simple partial application (currying)
  • This makes it easy to make simple procedures from more complex ones
• car, cdr, and cons from LISP
  • A pair of values can be stored in a single variable
  • This allows for the creation of more complicated data types (especially linked lists)
• Conversion between REXX stem variables and LISP-style linked lists
  • This provides somewhat greater interoperability
• Lexical scope (kind of)

However, attempting to do this in REXX causes several issues:

• Performance will likely be an issue, since the library uses INTERPRET to perform function calls
• REXX's relatively low call stack limit (100) prevents the use of recursion for most tasks
• As REXX lacks true compound data types, all data must be stored in strings (ugh)
• Lexical scope is possible, but it is hardly elegant

In general, this is probably more of a hack than something of great practical value. Still, it is interesting to see how functional programming can be implemented in a language like REXX.

Why REXX?

In the first place, REXX is frequently used to complete the sorts of data processing tasks for which functional programming can be suitable. Secondly, this provides a way of allowing more powerful REXX programs without needing to implement OOP (which is unavailable on some REXX platforms).

In the second place, why not?

Inspiration

• Ramda, a functional programming library for JavaScript
• Scheme, a LISP dialect
• PHP's closure syntax