purescript-neon

Neon is a practical standard library for PureScript.

-- Find the sum of all the multiples of 3 or 5 below 1000.
-- <https://projecteuler.net/problem=1>
import Neon
main :: Eff (console :: CONSOLE) Unit
main = 1
  :upTo 999
  :filter (divisibleBy 3 || divisibleBy 5)
  :sum
  :print

Neon is written from the ground up to be useful and coherent. It has some guiding principles:

• If something is possible in JavaScript (and not a terrible idea), it should be possible in Neon. This means you can do "ab" + "cd", but you can't do "ab" + 3.

• Functions should take their subject last. This means add x y is really y + x. Consider calling functions with :, like y :add x.

• Everything should be documented with examples. Type signatures are not a substitute for documentation.

• Laws should not prohibit useful instances. This means you can use or on booleans and arrays.

• There should be no type class hierarchy. This means HasZero does not imply HasAdd. If you need both, add both to your type signature.

• There should be as few operators as possible. This means <$> does not exist. Use map instead.

• There should be one obvious way to do things. This means return is not an alias for pure. In fact, it doesn't exist at all.

• Functions should be defined in type classes. This means add can be used for both numbers and strings.

• Type classes should be as small as possible. This means the Bounded type class is split into HasBottom and HasTop.

• Type classes should be designed for programmers, not mathematicians. This means HasAdd is a semigroup, but it's not called Semigroup.

• Neon should not define its own data types. That means you can use Maybe from Data.Maybe without translation.

• Pure functions should not throw exceptions. This means fromInt returns a Maybe value. Pure functions that throw exceptions should be marked unsafe.

• Qualified imports are annoying, and fewer imports are better. This mean import Neon is enough. No need for tens of lines of imports.