Add function(s) for converting Numbers to Strings

[sharkdp]

As suggested by @natefaubion here. /cc @hdgarrood

It would be interesting to have a few basic functions for converting Numbers to a String.

There are several packages dealing with (pretty) printing of numbers already:

• purescript-number-format (@Jonplussed) - exports some available methods from JavaScript (toExponential, toFixed, toPrecision) and defines a few convenient helper functions (toString, toHexString, ..).
• purescript-format (@sharkdp) - pretty printing of integers and numbers, Monoid-based interface for defining the style.
• purescript-formatters (@slamdata) - more ambitious project, also does date/time formatting.

In my opinion, merging purescript-number-format into this package or implementing a similar functionality would be the best option. The API of purescript-format is probably "too opinionated" for a low-level module like this.

What do you think?

[hdgarrood]

Yep, sounds sensible to me.

[hdgarrood]

One suggestion I'd have is to have newtypes for the scale or radix arguments in functions like toExponential so that actually formatting the number gives you a String and not a Maybe String.

[hdgarrood]

Newtypes where the constructor is not exported, that is, so that you can guarantee the value is within the range it needs to be in.

[sharkdp]

I went with a slightly different approach now, but it goes in a very similar direction to what you proposed.

https://github.com/sharkdp/purescript-numbers/blob/21cf05da5727969bb3e9ea08b45c30de68cafc14/src/Data/Number/Format.purs#L37-L62

It can be used like this:

> let x = 1234.56789

> toStringWith (precision 6) x
"1234.57"

> toStringWith (fixed 3) x
"1234.568"

> toStringWith (exponential 2) x
"1.23e+3"

[hdgarrood]

Looks really nice, great work :)