#    
#  Overview
The **`IndexFunc`** **function** is used to find the index of the first appearance of a Unicode code character in a string, such that it satisfies the provided function. 

To use this function, we must import the `strings` package in our file and access the `IndexFunc` function within it, using the `.` notation (`string.IndexFunc`).
##  
## Function definiton
Here is the definition of the `IndexFunc` function:

func IndexFunc (str string, fun func(rune) bool) int

## Parameters

The `IndexFunc` function takes two arguments:

- **`str`**: This is an argument of type `string`. It represents the list of characters that we want to search.

- **`fun`**: This argument represents the function that takes a `rune` as an argument and returns a `boolean` variable.

## Return value
The `IndexFunc` function returns the index where it finds the first instance of a character that the function `fun` returns `True` on. If there is no such character in the whole string, then `-1` is returned.


## Code

In the code given below, we use the `IndexFunc` function to find the position of the first Greek letter that appears in a `string`:


package main

import (
	"fmt"
	"strings"
	"unicode"
)

func main() {

	fun := func(r rune) bool {
		return unicode.Is(unicode.Greek, r)
	}

	str := "The greek letter α is used often in mathematics"
	x := strings.IndexFunc(str, fun)

	fmt.Println("a greek alphabet appears at position: ", x)
}

> Note: The `unicode` package is imported here, so that we can use the **`unicode.Is` function**. This function checks if a certain `rune` value is present in a list of Unicode values. In this case, the list consists of all Greek characters, which we get by using `unicode.Greek`.


The following example demonstrates a case where no character in the `string` satisfies the given function:

package main

import (
	"fmt"
	"strings"
	"unicode"
)

func main() {

	fun := func(r rune) bool {
		return unicode.Is(unicode.Greek, r)
	}

	str := "Educative Inc."
	x:= strings.IndexFunc(str, fun)

	if x == -1{
		fmt.Println("could not find any greek alphabets in : \"",str, "\"" )
	}
}

What is the IndexFunc function in Golang?

Use IndexFunc from the strings package to find the index of the first Unicode character satisfying a function. Returns -1 if not found.