Editing Programming language (section)

====Static and dynamic typing====
In [[static typing]], all expressions have their types determined before a program executes, typically at compile-time.<ref name="typing"/> Most widely used, statically typed programming languages require the types of variables to be specified explicitly. In some languages, types are implicit; one form of this is when the compiler can [[type inference|infer]] types based on context. The downside of [[implicit typing]] is the potential for errors to go undetected.{{sfn|Sebesta|2012|p=211}} Complete type inference has traditionally been associated with functional languages such as [[Haskell]] and [[ML (programming language)|ML]].<ref>{{Cite conference |last=Leivant |first=Daniel |date=1983 |title=Polymorphic type inference |conference=ACM SIGACT-SIGPLAN symposium on Principles of programming languages |language=en |location=Austin, Texas |publisher=ACM Press |pages=88–98 |doi=10.1145/567067.567077 |isbn=978-0-89791-090-3|doi-access=free }}</ref> 

With dynamic typing, the type is not attached to the variable but only the value encoded in it. A single variable can be reused for a value of a different type. Although this provides more flexibility to the programmer, it is at the cost of lower reliability and less ability for the programming language to check for errors.{{sfn|Sebesta|2012|pp=212–213}} Some languages allow variables of a [[union type]] to which any type of value can be assigned, in an exception to their usual static typing rules.{{sfn|Sebesta|2012|pp=284–285}}