10. Function declarations

Functions can only be declared at the top level and all parameters must have a direction. P4 functions are modeled after functions as found in most other programming languages, but the language does not permit recursive functions.

\~ Begin P4Grammar [INCLUDE=grammar.mdk:functionDeclaration]

• [INCLUDE=grammar.mdk:functionPrototype]
  End P4Grammar

• Here is an example of a function that returns the maximum of two 32-bit values:
  Begin P4Example bit\<32> max(in bit\<32> left, in bit\<32> right) { return (left > right) ? left : right; }

  End P4Example

A function returns a value using the return statement. A function with a return type of void can simply use the return statement with no arguments. A function with a non-void return type must return a value of the suitable type on all possible execution paths.