There are several languages with type inference, although most can't infer types in all cases: Haskell, ML variants (SML, CaML, etc.), and Scala are the most t

There are several languages with type inference, although most can't infer types in all cases: Haskell, ML variants (SML, CaML, etc.), and Scala are the most thorough. There are some common language features that make type inference tough, most notably mutable data. It's difficult to infer the element type of an array unless you know where it's been, which can be difficult or impossible to know in situations involving separate compilation. Some ML variants can infer all types for programs that avoid using mutable data.