rve_expr :: Parser (AST' Text)
observe_expr =
    reserved "observe"
    *> (Observe
        <$> expr
        <*> expr
        )

ar
observe_expr :: Parser (AST' Text)
observe_expr =
    reserved "observe"
    *> (Observe
        <$> expr
        <*> expr
        )
observe_expr =
    reserved "observe"
    *> (Observe
        <$> expr
        <*> expr
        )