Programming languages differ along the axis of type systems: dynamically typed languages determine a variable's type at runtime from its assigned value and permit reassignment to different types, while statically typed languages check types before runtime (at compile time) and reject type mismatches as errors prior to execution. A language's typing discipline can further be classified as "strong" (rejecting implicit type coercion between incompatible types) or "weak"/"loose" (attempting implicit coercion to produce a value), and optional static typing (type hints/annotations) can be layered atop a dynamically typed core language without affecting runtime behavior. These typing distinctions belong to the theory of programming language design within computer science, and they interact with a language's type-composition constructs—union types, intersection types, structural interfaces/protocols, and callable/function type signatures—which define contracts over the shape and behavior of values.
Programming languages differ along the axis of type systems: dynamically typed languages determine a variable's type at runtime from its assigned value and permit reassignment to different types, whi…