Float

Floats are 64-bit IEEE-754 arithmetic, with what I hope are improvements. Dark's floats were designed to not support infinity or overflow. Those are sentinel values which can sneak into logic, and continue to propagate. Instead, we want to use results to handle these errors.

Dark v1 problems

Operators

Problem: Dark's operators (+, -, *, etc) work on integers. In Dark v1, we use Float::+ instead, which doesn't suck but isn't great

**Non-solution: **We speculated that we could use the editor to simply hide the Float:: part. However, that doesn't allow polymorphism, you can't have a library that takes numbers of any kind and (for example) sums them.

Solution: use traits to support reuse of common operators for different types

Status: Not spec'ed

Float entry problems that convert to 0

TODO

Status: Problem not understood

Inf and NaN

Problem: In Dark v1, it's possible to accidentally create Inf and NaN, but it was not really possible to use them.

Solution: prevent creating Inf or NaN. Any functions which (internally) create invalid floats will return Results instead.

Status: Spec'ed, not implemented

Negative 0.0

Problem: it's possible to have negative 0.0. This is a confusing part of floats.

Solution: TODO

Status: problem not understood, solution unknown

Support other representations

Problem: v1 only supports decimalized floats, like 5.6. It should also support exponent style like 6.02e23

Solution: Also support exponent format

Status: Representation is spec'ed. Interaction model not spec'ed.

Floats don't support negatives

Problem: same as ints

Solution: copy the proposed interaction model from ints

Status: not spec'ed

v2 spec

v2 language definition

Same as V1, except we represent a float better.

type Sign =
  | Plus
  | Minus

type floatRep = {
      wholeNumberPart : Int64,
      fractionalPart : Int64
      exponentExists : Bool
      exponentSign : Sign
      exponentPower : Int64
    }

type Expr =
  | EFloat of floatRep
  | ...

type Pattern =
  | PFloat of floatRep
  | ...

type Dval =
  | DFloat of double
  | ...

type DType =
  | TFloat
  | ...

Examples

• 5.
• .6
• 0.6
• -678.234
• -6.436E-567

Float stdlib functions

type Error =
  | FloatOverflowError

// same as v1
Float::absoluteValue(Float: a) -> Float
Float::ceiling(Float: a) -> Int
Float::clamp(Float: value, Float: limitA, Float: limitB) -> Float
Float::floor(Float: a) -> Int
Float::greaterThan(Float: a, Float: b) -> Bool
Float::greaterThanOrEqualTo(Float: a, Float: b) -> Bool
Float::lessThan(Float: a, Float: b) -> Bool
Float::lessThanOrEqualTo(Float: a, Float: b) -> Bool
Float::max(Float: a, Float: b) -> Float
Float::min(Float: a, Float: b) -> Float
Float::negate(Float: a) -> Float
Float::round(Float: a) -> Int
Float::roundDown(Float: a) -> Int
Float::roundTowardsZero(Float: a) -> Int
Float::roundUp(Float: a) -> Int
Float::sqrt(Float: a) -> Float
Float::subtract(Float: a, Float: b) -> Float
Float::truncate(Float: a) -> Int
Float::sum(List Float: a) -> Float

// different from v1
Float::add(Float: a, Float: b) -> Result (Float, Error)
Float::subtract(Float: a, Float: b) -> Result (Float, Error)
Float::divide(Float a, Float b) -> Result (Float, Error)
Float::power(Float base, Float exponent) -> Result (Float, Error)
Float::multiply(Float: a, Float: b) -> Result (Float, Error)