Lua for REXX developers

If you are a REXX developer, you might find the following tips useful.

Data types

Data in REXX is untyped; or rather, there is only one data type: string.

Lua has several types.

From Programming in Lua:

Lua is a dynamically typed language. There are no type definitions in the language; each value carries its own type.

Logical expressions

In REXX, logical expressions return 0 or 1.

From the Lua Reference Manual:

The operator and returns its first argument if it is false; otherwise, it returns its second argument. The operator or returns its first argument if it is not false; otherwise, it returns its second argument.

For example:

nil or "a" --> "a"

This behavior is useful for specifying default values for function arguments:

function f(x)
  x = x or 1 -- Default value is 1
  --- Do something with x
end

Parsing

If you're looking for a Lua equivalent to the REXX PARSE statement, see:

The Simple Input Patterns (SIP) functions supplied by the Penlight extension.
The Lpeg extension.

Tables, not stem variables

Where you would use a stem variable in REXX you would likely use a table in Lua.

Modular programming

If you develop a Lua function that you want to use in more than one Lua program, you can store the function code in a Lua program, and then use the require function in other Lua programs to refer to that Lua program.

For example, suppose that you have developed a function named hello that you want to reuse. You store that function in a Lua program:

-- common.lua
local M = {}

-- Locally scoped ("private") function:
-- not available outside this chunk (file)
local function greeting(s)
  print(M.who .. " says, " .. "\"" .. s .. "\"")
end

M.who = "Lua"

function M.hello()
  greeting("Hello, World!")
end

-- Returns a table that contains
-- the hello function and the who variable
return M

then use the hello function in a Lua program like this:

local cmn = require("common")
cmn.hello() --> Lua says, "Hello, World!"
cmn.who = "Simon"
cmn.hello() --> Simon says, "Hello, World!"

The common.lua program must be stored in a path that is referred to by the Lua package.path property.

Manual