S-Expr: Parameter bindings created multiple times from unknown variable

[ashiven]

The following term gets translated to slotted-sexpr incorrectly:

fun extern binding(n1 n2: Nat, arg: «%core.nat.mul (n1, n2); Nat»): «%core.nat.mul (n1, n2); Nat» =
    let mapper = %rise.map @(%core.nat.mul (n1, n2)) f;
    return (mapper arg);

The resulting sexpr creates two invalid bindings for n1 and n2 that extract from some variable that was never bound:

(root extern binding
    (fun
        $_41120
        (scope
            (lit ff Bool)
            (let
                $n1_41093
                (scope
                    (extract
                        (var $_41092)          <-------------- never bound
                        (lit 0 (idx (lit 3 Nat))))
            (let
                $n2_41094
                (scope
                    (extract
                        (var $_41092)          <-------------- never bound
                        (lit 1 (idx (lit 3 Nat))))
            (let
                $return_41139
                (scope
                    (extract
                        (var $_41120)
                        (lit tt Bool))
            (let
                $n1_41132
                (scope
                    (extract
                        (extract
                            (var $_41120)
                            (lit ff Bool))
                        (lit 0 (idx (lit 3 Nat))))
            (let
                $n2_41133
                (scope
                    (extract
                        (extract
                            (var $_41120)
                            (lit ff Bool))
                        (lit 1 (idx (lit 3 Nat))))
...