> For the complete documentation index, see [llms.txt](https://ineelhere.gitbook.io/code-with-go/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ineelhere.gitbook.io/code-with-go/15-closure.md).

# Closure

This Go program demonstrates the use of closures by defining a function that returns another function.

```go
// Importing the "fmt" package, which provides functions for formatted I/O.
import "fmt"

// Function intSeq returns a closure: a function that "closes over" the variable i.
// The returned function can be used to generate a sequence of increasing integers.
func intSeq() func() int {
    // Initialize a variable i.
    i := 0

    // Define and return an anonymous function (closure) that increments and returns i.
    return func() int {
        i++
        return i
    }
}

// The main function, which serves as the entry point for the program.
func main() {
    // Call intSeq, which returns a function that will generate a sequence of integers.
    nextInt := intSeq()

    // Call the returned function, printing the next value in the sequence.
    fmt.Println(nextInt())

    // Call the returned function again, printing the next value in the sequence.
    fmt.Println(nextInt())

    // Call the returned function once more, printing the next value in the sequence.
    fmt.Println(nextInt())

    // Call intSeq again, creating a new closure with its own "i" variable.
    newInts := intSeq()

    // Call the new closure, printing the first value in its own sequence.
    fmt.Println(newInts())
}
```

#### Output

```
1
2
3
1
```

Now, let's break down the code and explain each part:

1. **Function Declarations:**
   * `intSeq() func() int`: This function returns another function (a closure) that generates a sequence of increasing integers. The returned function "closes over" the variable `i`.
2. **Main Function:**
   * `main()`: This is the entry point of the program.
   * `nextInt := intSeq()`: Calls `intSeq`, which returns a closure (a function that increments and returns `i`). The closure is assigned to the variable `nextInt`.
   * `fmt.Println(nextInt())`: Calls the closure (stored in `nextInt`), printing the next value in the sequence.
   * `fmt.Println(nextInt())`: Calls the closure again, printing the next value in the sequence.
   * `fmt.Println(nextInt())`: Calls the closure once more, printing the next value in the sequence.
   * `newInts := intSeq()`: Calls `intSeq` again, creating a new closure with its own `i` variable.
   * `fmt.Println(newInts())`: Calls the new closure, printing the first value in its own sequence.