Syntax Addition

wiki

After the changes bellow in the Lua source we can write:

if !b then a = c end
if a != c then a = c end

and it still works with the originals

if not b then a = c end
if a ~= c then a = c end

Comments

I agree with !=, especially as ~= is not widely used elsewhere and could be confused with Perl's =~. However, ! for not is bad, as it goes against Lua's rule of using words rather than symbols (compare with and and or). -- ReubenThomas

~ is a valid mathematical symbol for logical negation [1]. In programming languages, it is less common. However, even in languages like C, ~ is used for the closely related bitwise negation, while ! is used for logical negation, and != is used for inequality (i.e. !(a==b)). So, Lua's ~= has a small resemblance. However, C is inconsistent between bitwise and logical operations: & and &&, | and ||, and ~ and ! -- why not ~~ for logical negation to avoid a different character? In Lua, you might alternately do not(a==b). -- DavidManura

Or perhaps instead use <> as per Basic... thus requiring only the three comparison characters <, >, = for all tests. The ~ character is currently unique in Lua as being the only one that starts a multi-character lexical item while not being one itself! Also, <> matches the <= usage, so that x<=y means x<y or x=y while x<>y means x<y or x>y. Consistent. -- PeterHill

IMO, <> for inequality is a bad idea. The are data for which < and > may make no sense at all. For points in space, e.g., you may define equality and inequality, but there is no linear ordering. Yet you may still want to have a test for (in)equality of points, and <> might be misleading. -- Hgr

It is only consistent if you have complete [2] ordering. Otherwise it is possible for all three of <, > and == to be false. Even though ~ is annoyingly difficult to type on a Spanish Windows keyboard, which I am currently using to write this message, I have gotten used to it -- and I certainly wouldn't want to have to change all of the code I've got kicking around. Someday we will all have Unicode and be able to use &U+2260; which refuses to render itself on this Wiki. -- RiciLake

Using ! as negation would certainly make picking up Lua somewhat less annoying for programmers of most other languages. Which other languages even use ~ as negation? It's just odd, especially when ~ is used in other languages for things other than negation. Nobody said anything about replacing ~ as negation, simply adding ! as an alternative. So all your existing code continues to work perfectly and doesn't have to be touched at all. --DanHollis?

For what it's worth: Smalltalk, Dylan, and Matlab all use ~= for some kind of inequality according to the [Syntax Across Languages] page. (They also use ~ as the prefix for logical not.) As I understand, it's fairly common to write logical negation (in the mathematical sense) with a ~ prefix, so the use of ~= to mean not equivalent seems like a perfectly natural extension. --TaylorVenable

Supporting both symbols, as suggested above, complicates an otherwise simple language. -- DavidManura

On some keyboards, the ~ is difficult to find and to use. For instance, on azerty, you have to do [alt gr]+[3]+[anykey] to type one. -- anonymous

Wiki Note: The name of this page (SyntaxAddition) is not very descriptive. Perhaps NegationSyntax? would be better.