assignment :: Parser (String, Expression)
assignment = do
  name <- identifier
  equal
  expr <- expression
  return (name, expr)

-- | AssignExpr ::= set Identifier = Expression
assignment :: Parser (String, Expression)
assignment = do
  name <- identifier
  equal
  expr <- expression
  return (name, expr)

-- | AssignExpr ::= set Identifier = Expression
assignment = do
  name <- identifier
  equal
  expr <- expression
  return (name, expr)

-- | AssignExpr ::= set Identifier = Expression