1 files changed, 26 insertions, 0 deletions
diff --git a/src/Helper.hs b/src/Helper.hs
new file mode 100644
index 0000000..a8e393e
--- /dev/null
+++ b/src/Helper.hs
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+module Helper where
+
+import           Control.Monad.State
+import           Text.Parsec             hiding ( State )
+
+data Error = SyntaxError ParseError | UndeclaredFunction String | DuplicateFunction String | InvalidIndex Int | FatalError String
+instance Show Error where
+  show (SyntaxError        err) = show err
+  show (UndeclaredFunction err) = "ERROR: undeclared function " <> show err
+  show (DuplicateFunction  err) = "ERROR: duplicate function " <> show err
+  show (InvalidIndex       err) = "ERROR: invalid index " <> show err
+  show (FatalError         err) = show err
+type Failable = Either Error
+
+data Expression = Bruijn Int | Variable String | Abstraction Expression | Application Expression Expression
+  deriving (Ord, Eq)
+data Instruction = Define String Expression | Evaluate Expression | Comment String | Load String
+  deriving (Show)
+instance Show Expression where
+  show (Bruijn      x        ) = show x
+  show (Variable    var      ) = show var
+  show (Abstraction exp      ) = "[" <> show exp <> "]"
+  show (Application exp1 exp2) = "(" <> show exp1 <> " " <> show exp2 <> ")"
+
+type Environment = [(String, Expression)]
+type Program = State Environment