Reallow float ranges in random module

[mratsim]

Fix #11198 while preserving #10998 fix for #7698

[krux02]

And here the tail of pull requests of regarding float ranges begins. I see 19 more issues and pull requests related to float ranges.

Anyway, maybe you should mention in a comment that for float ranges the upper bound is exclusive.

[kaushalmodi]

@mratsim While you are working on this PR, can you add the spaces around dotdot in the above 3 doAsserts too?

PS: I am wondering how the doAsserts on rands always pass .. How is it predicted that the first two rands will always give 4, and the third will always give 6?! Seems like one or more of those doasserts is bound to fail some time.

[mratsim]

It's not float range as in range[0.0..1.0] but float slices HSlice[float, float] that were disabled though.

[krux02]

I always get confused about ranges and slices. In my opinion they should be ranamed to range and RangeType or something. It will open up the Identifier Slice for other use cases (I could use it). But that is another topic.

Try this in your code and tell me what you think about it:

import random

var a : 0 .. 10

var bins: array[0..10, int]

for i in 0 .. 100:
  let x = rand(a.type)
  bins[x] += 1

echo bins

bins = default(typeof(bins))

var b : 0.0 .. 10.0

for i in 0 .. 100:
  let x = rand(b.type)
  bins[int(floor(x))] += 1

echo bins

I can't test it right now, but I know what will happen. I think you can't do anything about it, but I think this pitfall is something that could be mentioned int he documentation.

[mratsim]

Array ranges are transformed into slices by type but range types are not

binning.nim(18, 15) Error: type mismatch: got <type range 0.0..10.0(float64)>
but expected one of: 
proc rand(max: int): int
proc rand[T: Ordinal or SomeFloat](x: HSlice[T, T]): T
proc rand(r: var Rand; max: Natural): int
proc rand[T](r: var Rand; a: openArray[T]): T
proc rand(max: float): float
proc rand[T: SomeInteger](t: typedesc[T]): T
proc rand(r: var Rand; max: range[0.0 .. high(float)]): float
proc rand[T](a: openArray[T]): T
proc rand[T: Ordinal or SomeFloat](r: var Rand; x: HSlice[T, T]): T

expression: rand(type(b))

Reworked:

import random, math

var a : 0 .. 10

var bins: array[0..10, int]

for i in 0 .. 100:
  let x = rand(a.type)
  bins[x] += 1

echo "int:", bins

bins = default(typeof(bins))

var b : 0.0 .. 10.0

for i in 0 .. 100:
  let x = rand(0.0 .. 10.0)
  bins[int(floor(x))] += 1

echo "float:", bins

Result

int:[6, 14, 8, 7, 4, 18, 5, 11, 10, 8, 10]
float:[12, 9, 8, 10, 13, 10, 11, 3, 16, 9, 0]

So yeah the 11th bin is empty but it's the integer ranges being inclusive that is unusual and ..< is good enough for me. Other languages struggle when inclusive integer bounds are needed. I never needed inclusive floats though.