module Hajspy where

data Expr = Var String
          | Expr :@: Expr       -- function application
          | Neg Expr            -- unary prefix -
          | Expr :*: Expr       -- infix *
          | Expr :/: Expr       -- infix /
          | Expr :+: Expr       -- infix +
          | Expr :-: Expr       -- infix -
          | Cond Expr Expr Expr -- "x if c else y" -> Cond c x y, note order change
          | Lambda String Expr
    deriving (Eq, Show)

{-
What does "Expr :@: Expr" mean? Answer:

If you understand "App Expr Expr" as saying that App is a data constructor with
two fields, then "Expr :@: Expr" means the same thing, except that the data
constructor is :@: and uses infix syntax. This is in hope that

    f :@: x :@: y

looks nicer than

    App (App f x) y

Similarly for the others.  See testParser.hs for usage examples.

And below specifies their precedence and associativity.
-}

infixl 9 :@:
infixl 7 :*:, :/:
infixl 6 :+:, :-: