Can we please add predicate functions to Float that test for +Infinity, -Infinity and NaN. Haskell's GHC does it with FFI calls.

Good idea.

I think we can just have Float.Infinity : Float and Float.NegativeInfinity : Float and Float.NaN as builtins, and then the pretty-printer can use the names for these builtins when printing floats.

https://github.com/unisonweb/unison/blob/trunk/docs/adding-builtins.markdown is (I think?) mostly up to date if you feel like having a go at this one. :)

These comments from primFloat.c say how to test for these:

   /* Floating point NaN iff exponent is all ones, mantissa is
      non-zero (but see below.) */

    /* A float is Inf iff exponent is max (all ones),
       and mantissa is min(all zeros.) */

    /* A (single/double/quad) precision floating point number
       is denormalised iff:
        - exponent is zero
	- mantissa is non-zero.
        - (don't care about setting of sign bit.)
    */

    /* sign (bit 31) set (only) => negative zero */

@philderbeast ah that's a good point, if we just have a bitwise cast from Float to Nat then we can just write these in pure unison. I think I like that better.