Initial commit + basic Expr impl

src/Language/Bergamot/Syntax.purs

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+module Language.Bergamot.Syntax where
+
+import Data.List (List)
+import Data.Functor (class Functor, (<$>))
+import Data.Eq (class Eq)
+import Data.Traversable (class Traversable, sequence)
+import Data.Foldable (class Foldable, foldr, foldl, foldMap)
+import Data.Monoid ((<>), mempty)
+
+data Expr v
+    = Var v
+    | Atom String (List (Expr v))
+
+derive instance Eq v => Eq (Expr v)
+derive instance Functor Expr
+
+instance Foldable Expr where
+    foldr f b (Var x) = f x b
+    foldr f b (Atom _ xs) = foldr (\x b' -> foldr f b' x) b xs
+
+    foldl f b (Var x) = f b x
+    foldl f b (Atom _ xs) = foldl (foldl f) b xs
+
+    foldMap f (Var x) = f x
+    foldMap f (Atom _ xs) = foldl (<>) mempty (foldMap f <$> xs)
+
+instance Traversable Expr where
+    sequence (Var f) = Var <$> f
+    sequence (Atom name fs) = Atom name <$> sequence (sequence <$> fs)
+
+    traverse f e = sequence (f <$> e)

src/Main.purs

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+module Main where
+
+import Prelude
+
+main :: Unit
+main = unit