_expr :: Parser (AST' Text)
call_expr =
    foldl App
        <$> (Var <$> identifier)
        <*> parens (commaSep expr)

re
call_expr :: Parser (AST' Text)
call_expr =
    foldl App
        <$> (Var <$> identifier)
        <*> parens (commaSep expr)
call_expr =
    foldl App
        <$> (Var <$> identifier)
        <*> parens (commaSep expr)