What makes Lua a cool programming language?

Why-is-Lua-So-Cool.txt

What makes Lua a cool programming language?

* You can mix imperative, OOP, or functional programming styles.
* Can execute as a file, interactively in a REPL[1], or be embedded.
* Highly portable, extensible, and has an excellent C API[2].
* Compact and headless; you add packages to extend capabilities.
* Supports packages and modules[3]; package manager is 'LuaRocks'.

* Dynamic typing[4] & dynamic structures; easily polymorphic.
* Lua has only 8 data types[5]; all are first-class values.
* Strings are 8-bit clean, conv to/from byte arrays, support unicode.
* Strings have pattern-matching with captures (very regex-like).

* Multiple return values!  Allows constructs such as x,y = y,x.
* Variadic parameters/return values, easily defaulted & looped over.
* Tables! Can be created as maps, arrays[6], or both simultaneously.
* Metatables! Can define default values & behaviors for tables[7].
* Lua OOP is prototype-based; syntactic sugar includes 'self'.
* Reflective global environment; can be manipulated at run-time.

* All functions are unnamed full lexical closures (lambdas).
* Loops can be controlled via user-defined iterator functions.
* Proper tail call elimination; allows deep recursion.
* Coroutines (co-operative multitasking); can be used for iterators.

* Automatic memory management (GC), 'weak' tables, finalizers.
* Block comments can encapsulate code that includes comments.
* You can have apps in other languages call out to Lua code.
* You can have Lua apps call out to code in other languages.
* 'luajit' (based on Lua 5.1) is 10x faster than the interpreter.
 
[1] REPL = "Read, Evaluate, Print, Loop" (a fancy acronym alternative to 'CLI').

[2] Lua's C API is based on a stack used to exchange parameters & return values.

[3] Packages were introduced to Lua in version 5.1 (the current version is 5.4).

[4] Variables aren't typed; variable values are. The 'type()' function will 
    reflect the type of an expression or the value that a variable holds.

[5] Lua's built-in data types are nil, boolean, number, string, table, function, 
    thread, userdata.  All numbers in Lua are IEEE-754 doubles, which can hold 
    exact integers up to 2^53. (There is a library for I32 bit manipulation.)

[6] Arrays in Lua (as with Julia, R, Smalltalk, Fortran, et al) are 1-based. 
    Tables allow construction of matrices, linked lists, sets & bags, etc.

[7] Metatables unlock all sorts of capabilities, such as table typing, defaulted 
    field values, read-only tables, reference logging/tracing, type-specific 
    methods, single- and multiple-inheritance, etc.  Each data type can have a 
    metatable; a metatable for 'string' is pre-defined.  Individual tables and 
    userdata items can have their own metatables.