My wish list

[Egor Skriptunoff <egor.skriptunoff@...>]

Hello, Lua people!


I have some suggestions.
Please, take a look.

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1)
This function will be useful:
bit32.weight(n) == Hamming weight of n 
(also known as population count, 
binary digit sum, count of set bits)

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2)
Frequently both quotient and remainder are needed.
Let % operator returns pair of values:
a % b == a-floor(a/b)*b, floor(a/b)

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3)
Lua lacks fast function to build initialized
array.  A function like this will be useful
if implemented in C:

function table.new(size, value)
  value = value or 0
  local t = {}
  for i = 1, size do
    t[i] = (type(value)=='function')
           and value(i) or value
  end
  return t
end

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4)
Why table.concat() works only with tables of 
strings and numbers?
table.concat() may use tostring() to work with 
arrays of any objects.

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5)
Syntactic sugar needed for primitive equality.
Let a===b denotes rawequal(a,b)
Inspired by Smalltalk :)

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6)
Why equality operator is so special in Lua?
Any string or any number is always not equal 
to any table despite of __eq field in metatable.
Example: it is impossible to implement rational
numbers in nice manner:
  local r = rationalNumber '1/12'
  r = '2/3' - 2*r            -- ok
  assert(r >  '1/3')         -- ok
  assert(r >= '1/2')         -- ok
  assert(r <= '1/2')         -- ok
  assert(r == '1/2')         -- never
  -- a blot on the landscape  :(
Please let __eq metamethod to decide 
whether values of different types are equal.
It will be useful for DSL Lua scripts,
where comparison of object and string is handy.

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7)
Here is my suggestion about comparison operators.

Comparison operators should return:
**) nil, if values are not comparable
      (3 > 'Hello') == nil
      (3 == 'Hello') == nil
**) false, if opposite comparison holds
      (3 > 5) == false  -- because (3<=5)==true
      (3 == 5) == false -- because (3~=5)==true
**) any true value (i.e., except nil and false),
    if comparison holds
      (3 < 5) == true
      (3 ~= 5) == true


How to calculate undefined operators:

Opposite operators should preserve nil values:
*) a ~= b should be calculated as
        if (a==b)==nil then return nil
        else return not(a==b) end

If only __lt is defined in metatable, then:
*) a <= b should be calculated as 
        if (a>b)==nil then return nil 
        else return not(a>b) end
*) a == b should be calculated as 
        if (a>b)==nil then return nil 
        else return not((a>b)or(a<b)) end

If only __le is defined, then:
*) a < b should be calculated as
        if (a>=b)==nil then return nil
        else return not(a>=b) end
*) a == b should be calculated as 
        if (a>=b)==nil then return nil
        else return (a>=b)and(a<=b) end

If only __eq is defined, then:
*) a < b should be calculated as
        return nil
*) a <= b should be calculated as 
        return nil

If both __lt and __le are defined:
*) a == b should be calculated as 
        if (a>=b)==nil then return nil
        else return (a>=b)and(a<=b) end

If both __lt and __eq are defined:
*) a <= b should be calculated as 
        if (a==b)==nil then return nil
        else return (a==b)or(a<b) end

If both __le and __eq are defined:
*) a < b should be calculated as 
        if (a==b)==nil then return nil
        else return (not(a==b))and(a<=b) end

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And some questions:

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8)
PiL book says, "The generic loop shares 
two properties with the numeric loop: 
the loop variables are local to the loop body 
and you should never assign any value to them."

Question: does generic loop variables indeed 
sensitive to assigning values to them?

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9)
Who are the author of bright idea about _ENV upvalue?
Sandboxing in Lua is perfect now.
I just want to say thank you.

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10)
Did anybody make attempt to write a specializer
for implementing Futamura-Turchin projections
in Lua (or in subset of Lua)?
(see "Partial evaluation" on Wikipedia for
brief description of the subject)

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-- Egor