3 ms·

Many languages do this (type inference), to some extent. The moment you have any expression that can evaluate to more than one type, though, it requires annotat

• hliyan 9y ago
  Are there any languages that do it beyond the first value assignment, or outside the current scope? Also, any languages that subsequently revise the type definition?
  • tedmiston 9y ago
    Not sure if this is exactly what you're asking but one can reassign variables to change their types in Python: >>> x = 1 >>> type(x) <class 'int'> >>> x = 'foo' >>> type(x) <class 'str'>
    • xapata 9y ago
      I believe the question was about inferred static typing for union types. Python does not do any static type inference. Also, I'm not sure how a union type could be distinguished from an error during type inference. Maybe a nullable, but otherwise it'd be very tricky.
• bitwalker 9y ago
  That's not always true, rank-1 polymorphic functions (i.e. functions polymorphic in their argument) don't usually require type annotations. Higher-rank polymorphic functions though do generally require them, because without the annotations type inference is undecidable in the general case for such functions. For example: pair x y = (x, y) This function creates a pair for any two types, and doesn't require any annotations.