pAssign :: Parser (Statement :~ SrcPos)
pAssign = withAnnotation $ do
  lv <- pLValue
  symbol ":="
  expr <- pExpression
  return $ Assign lv expr
pAssign :: Parser (Statement :~ SrcPos)
pAssign = withAnnotation $ do
  lv <- pLValue
  symbol ":="
  expr <- pExpression
  return $ Assign lv expr
pAssign = withAnnotation $ do
  lv <- pLValue
  symbol ":="
  expr <- pExpression
  return $ Assign lv expr