Using Emoji in Haskell

Question

I've recently come across a bot on Twitter named EmojiHaskell, that claims to tweet 'interpretable Haskell code with emoji variable names'. A particular Tweet caught my attention, as it looked like malformed syntax to me, so I decided to take a closer look. So far I've produced the following code:

module Main where

🙏 :: [🍳] -> Maybe 🍳
🙏 [] = Nothing
🙏 (👽:as) = Just 👽

main = print $ 🙏 "♥"

Since I've used λ on occasion in my Haskell code, I expected this code to work, but it appears that GHC doesn't like the emoji at all.

With $ runhaskell Main.hs I get:

Main.hs:4:1: parse error on input ‘🙏’

I've already had a look at the UnicodeSyntax extension, and tried to only use some or single emoji instead of all of them to see if a certain one provokes the problem.

Now my question is this: Is there currently a Haskell compiler that would accept the code? Can I get GHC to work with this code somehow?

Answer 1

That code is not valid haskell. The reason is that 🙏 (like, probably, all Emojis) is a symbol character:

Prelude> import Data.Char
Prelude Data.Char> generalCategory '🙏'
OtherSymbol

But you can still use them like any other symbol, namely as an operator:

Prelude Data.Char> let (🙏) = (+)
Prelude Data.Char> 32 🙏 42
74

Furthermore, as user3237465 pointed out, if you use the prefix syntax for operators, i.e. put it in parentheses, you can even use it like any other symbol:

(🙏) :: [a] -> Maybe a
(🙏) [] = Nothing
(🙏) ((👽):as) = Just (👽)

main = print $ (🙏) "♥"

This is almost the example in the original post. Unfortunately, this trick does not work for the type variable. The the documentation is worded a bit unfortunately, but in fact symbols are never type variables and always type constructors