Revive `boolean` type

[snoopcatt]

Hello! I'm here to resurrect the boolean type. Looks like it was dead a long time ago and buried in source code.

As for current Ravi version, there is zombie boolean type. Look:

local function bool(b: boolean)
        print(b, ravitype(b))
end

bool(true)

ravi: /home/ann/bool.ravi:0: type mismatch: expected boolean

Literally, boolean type exists, but it just does not work -- nor true nor false are "not boolean".

---

After some necromancy, boolean shows signs of life.

local function bool(b: boolean)
    print(b, ravitype(b))
end

bool(true)
bool('world')

true boolean src/ravi: /home/ann/bool.ravi:0: boolean expected

That works too:

local b: boolean = true
b = 123

src/ravi: b.ravi:4: Invalid assignment: boolean expected near <eof>

But I could forget to add it somewhere, please, double check it.

[XmiliaH]

It should be discussed if

local x:boolean
x = (function() return 1 end)()
print(x)

should error, since 1 is no boolean or convert 1 to a boolean. As

local x:number
x = (function() return "1" end)()
print(x)

does for strings.

[snoopcatt]

I think it shouldn't. Because in Lua representation, anything that is not nil or false considered as true.

It means that both 0 (number) and "0" (string) are true (boolean) in Lua world. Besides 0 and "1" we have also "true" and "false" strings.

---

But we may discuss implementation of explicit cast to @boolean(var). It should return:

• true if var == 1 (number) or "1" (string) or "true" (string)
• false if var == 0 (number) or "0" (string) or "false" (string)
• nil otherwise

function toboolean(v)
  if (v == 1 or v == '1' or v == 'true' ) then return true elseif (v == 0 or v == '0' or v == 'false') then return false end
end

[snoopcatt]

It should be discussed if

I implemented it in second commit. Seems to be working.

function test(i: integer) -- boolean
    return @boolean(i)
end

local x:boolean
x = (function() return 1 end)()
print(x)

print(test(1))

true true

But now I don't know, good it or bad, that string/number converting to boolean sometimes lol

[dibyendumajumdar]

In general - boolean is a dubious type in Lua. It was added just to allow something like NIL value in a table. Roberto has said many times he regrets adding this type. I want to understand what is the benefit of adding this type? Is there a good use case?