How to run existing program with yaegi cli and extend program’s functionality

[KiranSatyaRaj]

It is said that yaegi makes Go programs extensible, how can I test this on a program, in an interactive shell using yaegi cli, I made a simple program that gives the average which resides in the main(), and I want to extend the program by adding a new function that gives the median, now how can do this on an existing program using yaegi-cli, I'm just trying to learn what yaegi is, here the code of the program

package main

import "fmt"

func main() {
	nums := []int{1, 2, 3, 4, 5}
	sum := 0
	for _, num := range nums {
		sum += num
	}
	average := float64(sum) / float64(len(nums))
	fmt.Println("The average is", average)
}

and in the terminal, I enter yaegi interactive shell, now I want to test/make changes with respect to this program, like adding a new function that calculates the median, here's the program

func median(nums []int) float64 {
	sorted := make([]int, len(nums))
	copy(sorted, nums)
	sort.Ints(sorted)
	length := len(sorted)
	if length % 2 == 0 {
		return float64(sorted[length/2]+sorted[(length/2)-1]) / 2.0
	}
	return float64(sorted[length/2])
}

and run the fmt.Println("The median is", median(nums)) without explicitly having to declare nums
this is how I did it

$ yaegi run -i main.go
The average is 3
> func median(nums []int) float64 {
	sorted := make([]int, len(nums))
	copy(sorted, nums)
	sort.Ints(sorted)
	length := len(sorted)
	if length % 2 == 0 {
		return float64(sorted[length/2]+sorted[(length/2)-1]) / 2.0
	}
	return float64(sorted[length/2])
}
The average is 3
: 0xc000284330
> fmt.Println("The median is", median(nums))
main.go:1:64: undefined: nums

[mpl]

Hi.

what you're trying to do cannot work, because the nums variable from the main is local to the main function, it is not a global scope variable. So it is unknown when you're trying to give it as an argument to the median func(). It's as if you were trying to run that code:

package main

import (
	"fmt"
	"sort"
)

func oldmain() {
	nums := []int{1, 2, 3, 4, 5}
	sum := 0
	for _, num := range nums {
		sum += num
	}
	average := float64(sum) / float64(len(nums))
	fmt.Println("The average is", average)
}

func median(nums []int) float64 {
	sorted := make([]int, len(nums))
	copy(sorted, nums)
	sort.Ints(sorted)
	length := len(sorted)
	if length%2 == 0 {
		return float64(sorted[length/2]+sorted[(length/2)-1]) / 2.0
	}
	return float64(sorted[length/2])
}

func main() {
	oldmain()
	fmt.Println("The median is", median(nums))
}

Here is how it would look if you fixed your main to have a globar var instead:

% cat ./main.go 
package main

import (
	"fmt"
	"sort"
)

var nums = []int{1, 2, 3, 4, 5}

func main() {
	sum := 0
	for _, num := range nums {
		sum += num
	}
	average := float64(sum) / float64(len(nums))
	fmt.Println("The average is", average)
}
% 
% 
% yaegi run -i ./main.go 
The average is 3
> func median(nums []int) float64 {
	sorted := make([]int, len(nums))
	copy(sorted, nums)
	sort.Ints(sorted)
	length := len(sorted)
	if length%2 == 0 {
		return float64(sorted[length/2]+sorted[(length/2)-1]) / 2.0
	}
	return float64(sorted[length/2])
}
The average is 3
: 0xc00020e2b0
> 
> fmt.Println("The median is", median(nums))
The median is 3

[KiranSatyaRaj]

I was referring to the way I was able to extend the program without actually making changes to the existing program but doing it using yaegi-cli instead, making changes in real-time, and the code in the REPL knows that it's a part of the main.go file, I couldn't understand how the idea/implementation behind that works.

[KiranSatyaRaj]

hey @mpl , I cannot run the precompiled files, I get an error while doing so

yaegi run -i ./hello
./hello:1:1: illegal character U+007F
run: ./hello:1:1: illegal character U+007F

[mpl]

You're trying to run an interpreter on a compiled binary.

[KiranSatyaRaj]

You're trying to run an interpreter on a compiled binary.

Yes, I'm sorry, what was I thinking

[KiranSatyaRaj]

Hey @mpl, I'm unable to run this command, I removed all the binaries and pkgs, for installing the new go version, now I couldn't install yaegi-cli, can you please help me through?

sudo curl -sfL https://raw.githubusercontent.com/traefik/yaegi/master/install.sh | bash -s -- -b $GOPATH/bin v0.9.0
traefik/yaegi info checking GitHub for tag 'v0.9.0'
traefik/yaegi info found version: 0.9.0 for v0.9.0/linux/amd64
install: cannot create regular file '/bin/yaegi': Permission denied