functions

sfunction_definition:=

sfun_kind:=

functions | cfunCFunction

functions | genGenerator

functions | funFunction

The function kinds have the following semantics:

fun: An ordinary Felix function. Must not have side-effects. The representation is indeterminate, and may be a C++ class with an apply() method, an ordinary C function, or nothing if all applications are inlined away.
cfun: Enforces creation of a C style function.
gen: Create a generator. A generator is a function with side-effects, which includes any kind of object creation (such as a C++ string), or function which impacts external state such as malloc() or random().
Generator applications are always lifted out of expressions and the result of the application assigned to a temporary variable, which replaces the application in the original expression. This ensures a generator application is evaluated exactly one if the enclosing expression is evaluated. This feature is similar to C sequence points.

sfun_arg :=

functions | ( sparameter_comma_list when sexpr )

functions | ( sparameter_comma_list )

functions | NAME

fun_return_type:=

functions | : stypeexpr expect sexpr

functions | : stypeexpr

functions | expect sexpr

functions | epsilon(typ_none none)

A function return specification consists of an optional type and an optional expected postcondition. The special identifier result can be used in the postcondition to denote the returned value. If the postcondition is omitted it is quivalent to true, otherwise the postcondition is check after every application.

If the return type is not specified, the compiler will try to calculate it from the function definition. Occasionally this will fail for recursive functions due to the interaction with overloading and recursive types. Reusable library functions should always provide an explicit return type annotation.