Deriving requirements from operations
Operations impose constraints on the values they use. Arithmetic can constrain a parameter to a numeric type, while a homogeneous list relates its element types. An inference system combines these requirements and seeks a consistent assignment. Conflicting constraints should produce an error rather than an arbitrary choice that permits execution.
Fewer annotations, still static types
F# explicitly distinguishes omitted annotations from dynamic typing. Types are still established at compile time, with the compiler deriving information from context. Annotations remain useful for resolving ambiguity, constraining an interface, or documenting intent. Inference reduces repetitive declarations without removing the type system’s restrictions on valid operations.
References: [2]
Inferring reusable types
An identity function need not be restricted to integers: an inferred type variable can express that its input and output have the same unspecified type. This supports reusable functions. The available polymorphism and inference rules nevertheless depend on the language, and not every program can automatically receive an unrestricted most-general type.
Combining context and annotations
Literals, calls, and known interfaces can narrow the inferred result. F# examples show how a literal’s type affects parameters and return values; insufficient information may require an annotation. Inspecting inferred types can also reveal an unintended restriction introduced by the implementation of a function rather than by the inference mechanism itself.