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Advanced Functions and Procedures

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In this section, we will delve into advanced concepts related to functions and procedures in MUMPS. By the end of this module, you should be able to create more complex and efficient functions and procedures, understand the use of local and global variables within them, and handle recursion and higher-order functions.

Key Concepts

  1. Advanced Function Definitions
  2. Local and Global Variables in Functions
  3. Recursion
  4. Higher-Order Functions
  5. Practical Examples
  6. Exercises

  1. Advanced Function Definitions

Function Syntax Review

In MUMPS, functions are defined using the FunctionName^RoutineName syntax. Here’s a quick review of a simple function:

MyFunction(x)
    Q x*2

Advanced Function Features

  • Multiple Parameters: Functions can take multiple parameters.
  • Default Parameter Values: You can set default values for parameters.
  • Return Multiple Values: Although MUMPS functions traditionally return a single value, you can use arrays or global variables to return multiple values.

Example: Function with Multiple Parameters

SumAndProduct(a, b, .sum, .product)
    S sum=a+b
    S product=a*b
    Q

In this example, SumAndProduct takes two input parameters a and b, and two output parameters sum and product.

  1. Local and Global Variables in Functions

Local Variables

Local variables are defined within the scope of a function and are not accessible outside of it.

LocalExample()
    N x
    S x=10
    Q x

Global Variables

Global variables are accessible throughout the entire MUMPS environment.

GlobalExample()
    S ^globalVar=20
    Q ^globalVar

  1. Recursion

Recursion is a powerful technique where a function calls itself. It is useful for tasks that can be broken down into similar sub-tasks.

Example: Factorial Function

Factorial(n)
    I n=0 Q 1
    Q n*$$Factorial(n-1)

In this example, Factorial calls itself with n-1 until n is 0.

  1. Higher-Order Functions

Higher-order functions are functions that take other functions as parameters or return functions as results.

Example: Map Function

Map(array, func)
    N i, result
    S i=""
    F  S i=$O(array(i)) Q:i=""  S result(i)=$$@func(array(i))
    Q result

In this example, Map applies the function func to each element of array.

  1. Practical Examples

Example: Fibonacci Sequence

Fibonacci(n)
    I n=0 Q 0
    I n=1 Q 1
    Q $$Fibonacci(n-1)+$$Fibonacci(n-2)

Example: Sorting an Array

SortArray(array)
    N i, j, temp
    F i=1:1:$O(array(""),-1) F j=i+1:1:$O(array(""),-1) I array(i)>array(j) D
    . S temp=array(i)
    . S array(i)=array(j)
    . S array(j)=temp
    Q array

  1. Exercises

Exercise 1: Implement a Power Function

Write a function Power(base, exponent) that calculates the power of a number using recursion.

Power(base, exponent)
    I exponent=0 Q 1
    Q base*$$Power(base, exponent-1)

Exercise 2: Implement a Higher-Order Function

Write a higher-order function Filter(array, func) that filters elements of array based on the condition defined in func.

Filter(array, func)
    N i, result
    S i=""
    F  S i=$O(array(i)) Q:i=""  I $$@func(array(i)) S result(i)=array(i)
    Q result

Exercise 3: Implement a Function to Reverse a String

Write a function ReverseString(str) that reverses a given string.

ReverseString(str)
    N i, len, result
    S len=$L(str)
    F i=1:1:len S result=$E(str,i)_result
    Q result

Conclusion

In this module, we explored advanced functions and procedures in MUMPS, including handling multiple parameters, recursion, and higher-order functions. We also provided practical examples and exercises to reinforce these concepts. Mastering these advanced techniques will enable you to write more efficient and powerful MUMPS programs. In the next module, we will delve into database management with MUMPS.

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