haampie / ranges.jl Goto Github PK

Some ideas about ranges of integers in Julia. The package provides half-open ranges:

RightOpen(a, b)          # [a → b)
Reverse(RightOpen(a, b)) # [a ← b)
LeftOpen(a, b)           # (a → b]
Reverse(LeftOpen(a, b))  # (a ← b]

and some helper functions a : until : b and b : downuntil : a.

For example:

> using Ranges
> for i = 0 : until : 5
    print(i, ' ')
  end
0 1 2 3 4
> for i = LeftOpen(0, 5)
    print(i, ' ')
  end
1 2 3 4 5

> for i = rev(RightOpen(0, 5))
    print(i, ' ')
  end
4 3 2 1 0
> for i = 5 : downuntil : 0
    print(i, ' ')
  end
5 4 3 2 1

It solves a couple problems in the native range a:b-1 of Julia:

1. No overflow of length(a : until : b) by using UInts.

   > length(-10:typemax(Int))
   ERROR: OverflowError()

   vs

   > length(-10 : until : typemax(Int))
   0x8000000000000009

2. Iterate over unsigned integers in reverse order.

   > for i = 0x03:-1:0x00
       print(i, ' ')
     end
   ERROR: InexactError()

   vs

   > for i = rev(0x00 : until : 0x04)
       print(i, ' ')
     end
   3 2 1 0

3. Ability to construct an empty range 0x00 : until : 0x00.

At the moment one cannot iterate all the way from typemin(IntT) to typemax(IntT) inclusive; but this issue is best fixed with the new iterator protocol in Julia 1.0 combined which makes implementing a ClosedRange type a breeze.