Type hierarchies / implicit conversions

Scenarios where one type could be coerced to another — for example where a String is expected but a Number is given. Currently unsupported: unification rejects the mismatch outright. Adding support would require either explicit sub-typing relations or some form of conversion constraint. (TypeFighter does not do anything magical here — there's no automatic ToString or similar. The hypothetical behavior below is purely what the test would expect if conversions were wired in.)

implicit conversion from number to string

Not yet implemented

Env

concat : String -> String -> String

Source

concat 10 "Hello"

Inferred

String   (IF implicit Number → String conversion were allowed)

NOT YET IMPLEMENTED: implicit conversions. Today this fails with "Can't unify Number and String". Kept as an ignored test to mark the intended behavior.

F# test body

X.App (X.App (X.Var "concat") (X.Lit 10)) (X.Lit "Hello")
|> solve typeHierarchyEnv None
|> shouldSolveType (Mono BuiltinTypes.string)