Breaking Changes w/ Lua

While Erde attempts to keep most core behaviors consistent w/ Lua, there are a couple of minor breaking changes.

NEQ Operator: ~= vs !=

In Erde, the NEQ operator uses != instead of Lua's ~=. This is mainly because Erde keeps Lua's bit operators and allows for operator assignments w/ these operators. This means that ~= is already taken by the bitwise exclusive OR operator assignment:

local x = 5 -- 0b101
x ~= 3 -- 0b011
print(x) -- 6 (0b110)

Additionally, if we try to keep ~= from Lua, the most natural token for the logical unary NOT (that would replace the not keyword in Lua) would be ~. However, Lua already reserves the unary ~ operator token for the bitwise unary NOT operator:

local x = 5 -- 0b101
print(~x) -- 2 (0b010)

If Erde finds a ~= token being used as a binary operator, it will throw an error, suggesting the != operator instead:

if x ~= nil {
  ...
}

unexpected token '~=', did you mean '!='?

Function Call Parentheses

In Lua, function call parentheses are optional when there is only one argument and it is either a string literal or table constructor:

print "my message"
print { message = "my table" }

Erde does not support this syntax, that is, function calls always require parentheses. This forces consistency not only across the Erde projects, but also with many other programming languages:

print("my message")
print({ message = "my table" })

Significant Whitespace for Ambiguous Syntax

In Lua, there is an infamous ambiguous syntax involving immediately invoked function expressions (IIFE):

local x = y
(function() print('hello world') end)()

-- can be interpreted as either:
local x = y;
(function() print('hello world') end)()

-- or:
local x = y(function() print('hello world') end)()

Lua requires semicolons to differentiate these statements. You can still use semicolons in Erde, but Erde will also infer the user's intention based on the presence of newlines. If there is a newline before the IIFE, it is parsed as a separate statement. Otherwise, it is parsed as a chained function call.

-- parsed as two separate statements
local x = y
(() -> print('hello world'))()

-- parsed as one statement (chained function calls)
local x = y(() -> print('hello world'))()

Semicolons in Table Constructors

Lua allows for semicolons in table constructors, which, according to the docs, is usually used to delimit different sections in a constructor:

local x = { x = 10, y = 45; 'one', 'two', 'three' }

Erde does not support this syntax, as it not only causes inconsistencies in table constructor delimiters, but is also quite unreadable, since many are not even aware that such syntax is valid Lua.