#### §4.5.(d) Typing rules

A parameter mapping (implicit by parameter position or explicit by a `with` clause) is well typed if the right hand side conforms to the left hand side, either by

- type equality
- implicit primitive type conversion
- subtype polymorphism
- translation polymorphism, here: lifting;
  however, within `replace` bindings step 1 of the smart lifting algorithm (§2.3.3.(a)) is not applicable
- or by a combination of the above.

A result mapping (implicit or explicit by a `with` clause) is well typed, if the value at the left hand conforms to the right hand side according to the rules given above, except that translation polymorphism here applies lowering instead of lifting.

These rules define translation polymorphism as introduced in §2.3.

Additionally, in a `replace` callin binding compatibility of parameters and return types must hold in both directions. Thus, from the above list of conversions a replace binding cannot apply subtype polymorphism nor primitive type conversion. If more flexibility is desired, type parameters can be used as defined in §4.10.