Main.hs

{-# LANGUAGE GADTs #-}
{-# LANGUAGE TypeOperators #-}

module Main where

data a :=: b where
  Refl :: a :=: a

symmetric :: a :=: b -> b :=: a
symmetric ab = case ab of
  Refl -> Refl

main :: IO ()
main = do
  putStrLn "ほげほげ"

makefile

all: 
        rm -f Main.js
        hastec Main.hs
        rm -f *.hi; rm -f *.jsmod; rm -f *.o