Passing Functions as Arguments

Overview

This documentation explains how to pass functions as arguments to other functions in the Flow-Wing programming language. This feature allows for greater flexibility and modularity in code design.

Function Type Syntax

Flow-Wing represents function signatures with bracket notation:

[(param_types) -> return_type]

Examples:

• [(str) -> nthg] — function taking a string, returning nothing
• [(int, int) -> int] — function taking two ints, returning int
• [(int) -> bool] — predicate function

Simple Callback Example

Below is a simple example demonstrating a single-parameter callback:

fun greet(name: str) -> nthg {
  print("Hello, " + name)
}

fun runCallback(callback: [(str) -> nthg]) -> nthg {
  callback("World")
}

runCallback(greet)

Output: Hello, World

Example Code

Below is an example that demonstrates how to define and pass functions as arguments:

fun printX(x: int, y: deci, p: str, u: bool, callback: [(str) -> nthg]) -> nthg {
  print("Printing X:", x)
  print(y, p, u)
  callback("Hello") /; Calling the callback function
}

fun printString(message: str) -> nthg {
  print("\nFrom printString:", message)
}

fun mainFunction(handler: [(int, deci, str, bool, [(str) -> nthg]) -> nthg]) -> nthg {
  handler(2, 2.2, "Sample String", false, printString) /; Passing arguments and the function
}

mainFunction(printX) /; Calling mainFunction with printX as the handler

Explanation of Functions

printX

• Signature: fun printX(x: int, y: deci, p: str, u: bool, callback: [(str) -> nthg]) -> nthg
• Parameters:
  • x: An integer value to be printed.
  • y: A decimal value to be printed.
  • p: A string to be printed.
  • u: A boolean value to be printed.
  • callback: A function that takes a string as an argument and returns nothing (nthg).
• Description: This function prints the values of x, y, p, and u. It then calls the callback function with the string "Hello".

printString

• Signature: fun printString(message: str) -> nthg
• Parameters:
  • message: A string message to be printed.
• Description: This function prints the provided message. It is designed to be passed as a callback to other functions.

mainFunction

• Signature: fun mainFunction(handler: [(int, deci, str, bool, [(str) -> nthg]) -> nthg]) -> nthg
• Parameters:
  • handler: A function that matches the signature of printX.
• Description: This function accepts a handler function and calls it with specific arguments, including printString as the callback.

Usage

• The mainFunction is invoked with printX as the handler, demonstrating how to pass a function as an argument. When printX is executed, it prints the provided values and calls printString with a sample string.

Conclusion

Passing functions as arguments in Flow-Wing allows for more dynamic and reusable code. This pattern can be used to implement callbacks and event handling, making your code more modular and maintainable.