Updated lua basics (markdown)

lua-basics.md

@@ -21,16 +21,16 @@ Look for tutorials. Lua 5.1 to 5.4 all equally apply since the core language has
 - Use **==** to check for equality, **~=** to check for inequality (most other languages use **!=**, which does not exist in Lua)
 - The "table" is the only data structure that exists. They are arrays and hash maps in one.
 - Array indices start at 1 (not 0). This means an array A with N elements goes from A[1] til A[N].
-- A["key"] = 5 is the same as A.key = 5.
-- A[0] can be used normally, but will not be picked up by the # operator or ipairs().
+- A.key = 5 is syntax sugar for A["key"] = 5.
 - You can use any value except nil as a table key.
+- A[0], A[-42], etc. can be used normally, but will not be picked up by the # operator or ipairs(), because indices <= 0 end up in the hash part, not the array part of the table.
 - Table access:
   - Reading an index/key that doesn't exist returns nil
   - Writing an index/key that doesn't exist does an insert
     - `t[#t+1]` is one way to append a value to an array.
     - Alternatively, use `table.insert()`.
     - Write a *nil* value to erase a key
-- Array length (# operator) is defined as (x - 1) for any integer i that satisfies `i >= 0 and A[i+1] == nil`. If multiple such i exist you may get one or the other (Lua does a binary search internally to find a suitable index i)
+- Array length (# operator) is defined as an integer i that satisfies `i >= 0 and A[i] ~= nil and A[i+1] == nil`, ie. the index of some non-nil value followed by a nil. If multiple such i exist you may get one or the other (Lua does a binary search internally to find a suitable index i)
 - The ONLY values that are false-y in an if statement are false and nil. Anything else counts as true. Yes, 0, empty string, empty table all count as true-y. This is different in e.g. Python.
 - The global namespace can be accessed as the table _G (yes this is just a global symbol. Yes you can iterate over all globals and get a list of functions and constants that way.)
 - Any variable that is not marked 'local' is global. Variables not declared are assumed to be globals. That means if you want to call a function but typo the name, Lua will load the script without warnings. When the script is then run, Lua tries to fetch the typo'd symbol from _G, that fails so nil is returned; then it happily proceeds to call the result as a function, untilmately failing with "attempt to call a nil value".