A system and method can support compatibility checking in a programming language environment. The programming language environment can check whether a target type associated with an expression in the programming language environment is functional, wherein the target type is functional when it has exactly one method meeting one or more criteria that define that method as relevant in a counting system. Then, the programming language environment can derive a function descriptor from the target type, which is context-dependent. Furthermore, the programming language environment can type-check the expression with the function descriptor associated with the target type.