Strict semantics
(As opposed to non-strict semantics.)
In programming languages that use strict semantics, an undefined argument of a function leads to an undefined function result. This happens even if the argument's value isn't needed by the function:
∀ f . f undefined = undefined
As a result, the if ... then ... else ...
conditional usually requires additional support from such languages to work correctly - evaluate the condition, then the selected alternative (not both of them).
It may be implemented by eager evaluation. Examples of programming languages which use strict semantics include OCaml and LISP.