Lua

Lua is a scripting language first released in 1993, and particularly popular as an embedded language. This article compares Lua to MiniScript, and may be useful to people coming to MiniScript with a background in Lua.

For a side-by-side comparison on a collection of short programs, see here.

Similarities

Block Syntax

Both Lua and MiniScript delineate code blocks and control structures with explicit keywords. There are some minor differences in syntax, summarized in the table below.

Lua	MiniScript
function / end	function / end function
if / elseif / end	if / else if / end if
while ... do / end	while / end while
for i = 1, 10, 2 do / end	for i in range(1, 10, 2) / end for
repeat / until	(no direct equivalent)

The most notable difference is that while Lua uses end alone to terminate a function, if, while, or for block, MiniScript uses end function, end if, end while, and end for respectively. MiniScript lacks a repeat-until structure; the standard idiom is to use a while true (infinite) loop, and break out of it when termination conditions are met.

Data Types

Five of the seven basic types in Lua -- nil, number, string, function, and table -- have direct equivalents in MiniScript. nil is called null in MiniScript, and tables are called maps.

Strings in both languages are immutable. MiniScript strings are Unicode, and index by Unicode character; interpretation of Lua strings is implementation-dependent, and index by byte. While Lua has several ways of writing string literals, in MiniScript, string literals are always enclosed in double-quotes (and if you need a double-quote inside a string literal, write it twice, as in SQL).

greeting = "Hello, ""Bob""!  Pleased to meet you."
print greeting   // prints: Hello, "Bob"!  Pleased to meet you.

While MiniScript maps are conceptually quite similar to Lua tables, their syntax and usage is rather different; see the section on Maps under Differences.

Differences

Variable Scope

In Lua, variables are always global by default; you use the local keyword to explicitly declare a local variable. In MiniScript, variables are always local by default (and are never declared; they spring into being when you assign to them). To update a global variable in MiniScript from within a function, you would use the globals or outer prefix.

Lists

Perhaps the biggest difference between Lua and Python is in handling of array-like data. MiniScript has a list data type with no direct Lua equivalent. Readers comfortable with Python should think of it as a Python-style list; others may find the following table helpful.

Task	Lua	MiniScript
Create an array literal	a = {"one", "two", "three"}	a = ["zero", "one", "two"]
Print the first item in an array	print(a[1])	print a[0]
Print the entire array	print(table.concat(a, ", "))	print a
Get the length of an array	print(#a)	print a.len
Append an item to an array	table.insert(a, "foo")	a.push "foo"
Insert item at front of array	table.insert(a, 1, "hey")	a.insert 0, "hey"
Pop the last item off the array	last = table.remove(a)	last = a.pop
Pull the first item off the array	first = table.remove(a, 1)	first = a.pull
Remove item at index i	table.remove(a, i)	a.remove i
Get index of an array item	no standard method	idx = a.indexOf("two")
Get sub-array from i to j	no standard method	print a[i:j]

The key differences to note:

• MiniScript lists are 0-based, rather than 1-based
• MiniScript lists are manipulated by slicing or dot-syntax methods like len, insert, and remove, rather than by functions in the table module.
• MiniScript lists can safely contain null.
• MiniScript lists can be concatenated with the `+` operator.

Maps

Lua tables (when used as associative arrays, not list-style arrays) are similar in purpose to MiniScript maps, but there are a number of differences.

Maps in MiniScript can take any data type as keys. In map literals these keys use the same syntax as in any other context (unlike in Lua, where string keys are specified without quotes if they are valid identifiers, or with square brackets plus quotes otherwise). Instead of =, MiniScript uses : to separate the keys from the values.

Lua	MiniScript
d = {one=1, two=2, three=3, ["forty two"]=42}	d = {"one":1, "two":2, "three":3, "forty two":42}

Accessing items by key is done with square-brackets in both languages. When the keys are valid identifiers, MiniScript also allows dot syntax.

print d["one"]
d["one"] = "uno"
d.two = "dos"

Iterating over the key-value pairs is common in both languages, but the syntax is different. In MiniScript, iterating over a map gives you, on each iteration, a little map containing key and value.

Lua	MiniScript
for k,v in pairs(d) do print(k,v) end	for kv in d print kv.key + " " + kv.value end for

Commonly used map methods include len, remove, hasIndex, indexOf, indexes, and values. Note that len returns the number of key-value pairs in the map, which is different from both getn and # in Lua.

print "This map has " + d.len + " pairs in it."
print "The keys are: " + d.indexes
print "and values are: " + d.values
if d.hasIndex("two") then
   print """two"" is one of the indexes, and its value is " + d["two"]
else
   print "but ""two"" is not one of the indexes."
end if
print "The index that maps to ""uno"" is: " + d.indexOf("uno")

Maps can be combined with the `+` operator.

Strings

Strings in MiniScript and Lua are similar in most ways, though in MiniScript, all strings are composed of Unicode characters and indexing is always by character rather than by byte. The table below shows common operations in both languages.

Task	Lua	MiniScript
Assign a string literal	s = "Hello world!"	s = "Hello world!"
Print the first character of a string	print(string.sub(s,1,1))	print s[0]
Print all but the first 2 characters	print(string.sub(s,3)	print s[2:]
Get the length of a string	print(#s)	print s.len
Combine two strings	s = "Really... " .. s	s = "Really... " + s
Get index of a substring	idx = string.find(s, "world")	idx = s.indexOf("world")
Get substring from i to j	print(string.sub(i,j))	print s[i:j]