Selecting Help from !rlua's iconbar menu will open the front page of its manual. Click the right margin and the INDEX page will open. If you select standard lua reference manual from the Language Reference box on the right you will reach the official Lua 5.4 Reference Manual. This is useful not only as a reference to the functions built in to Lua's standard libraries, but as a summary of the language in general. RiscLua is 99.9% standard Lua with 0.1% extra functionality for use in RISC OS, about which the official Reference Manual cannot tell you.
A summary of features in RiscLua that are not in standard Lua.
The name of a variable in Lua must consist of letters, digits or underscores, but may not start with a digit. However, in RiscLua, variable-names can also contain the symbols !, ?, $ and @. Lua has a convention that names starting with an underscore are unofficially reserved. It is probably best for you to stick with lowercase letters and digits for the variable-names in your own programs.
If you accidentally enter a hard space character (ASCII 160) into the text of a RiscLua program it will be treated as a plain space (ASCII 32). This avoids the problem of invisible typographic errors.
RiscLua lets you use the backslash symbol \ as an abbreviation for the word function , and => as an abbreviation for the word return .
double = \ (x) => 2*x end print (double (7)) --> 14RiscLua lets you use operators followed by = as updaters, so that
x + = 7is equivalent to
x = x + 7RiscLua lets you unpack tables into local variables, so that
local x, y in tis equivalent to
local x, y = t.x, t.y
Beside the documentation that comes with !rlua there is a mass of material about Lua on the internet: videos, blogs, tutorials and books. I recommend in particular Programming in Lua (Fourth edition), by Roberto Ierusalimschy, as a work that should be of interest to programmers whatever the programming language they use.