Support for functions written in go when used as a library

[wader]

Hello! Would it be possible to add support for own "internal" functions written in go when using gojq as a library?
I had a quick look at the code and it seemed not that far away but maybe i'm missing something? If you think it's a good i would even be happy to try implement it if you give some pointers.

[itchyny]

I'm working on this in #46, and you will be able to define your internal function as follows. Any thoughts?

package main

import (
	"fmt"
	"log"

	"github.com/itchyny/gojq"
)

var compilerOptions = []gojq.CompilerOption{
	// gojq.WithFunction({function name}, {arity (argument count)}, {function})
	gojq.WithFunction("f", 0, func(x interface{}, _ []interface{}) interface{} {
		if x, ok := x.(int); ok {
			return x * 2
		}
		return fmt.Errorf("f cannot be applied to: %v", x)
	}),
	gojq.WithFunction("g", 1, func(x interface{}, xs []interface{}) interface{} {
		if x, ok := x.(int); ok {
			if y, ok := xs[0].(int); ok {
				return x + y
			}
		}
		return fmt.Errorf("g cannot be applied to: %v, %v", x, xs)
	}),
}

func main() {
	query, err := gojq.Parse(".[] | f | g(3)")
	if err != nil {
		log.Fatalln(err)
	}
	code, err := gojq.Compile(query, compilerOptions...)
	if err != nil {
		log.Fatalln(err)
	}
	iter := code.Run([]interface{}{1, 2, 3, 4, 5})
	for {
		v, ok := iter.Next()
		if !ok {
			break
		}
		fmt.Printf("%v\n", v)
	}
}

[wader]

Added some comments in the PR. API looks good to me.

[wader]

I do support optional arguments in my hack, but now when i think about it that might be bad and the correct way would be to use multiple WithFunction with different artity and then maybe share go code between them?

[wader]

Rebased and fixed my things on top of your branch, seems to work fine 👍

[itchyny]

I do support optional arguments in my hack, but now when i think about it that might be bad and the correct way would be to use multiple WithFunction with different artity and then maybe share go code between them?

That's exactly what I was concerned. And supporting same function name with different arities introduces a bit hacky code. I'm wondering making the second argument of WithFunction to []int, the list of acceptable arities.

[itchyny]

When I give up supporting adding the functions with the same name, the code would be clean. For example, using gojq.WithFunction("f", []int{0, 1}, F) and gojq.WithFunction("f", []int{2, 3}, G). Supporting all the f/0 to f/3 is difficult.

[wader]

I think in most cases you want min/max arg count range? gojq.WithFunction("f", [2]int{0, 1}, F) or gojq.WithFunction("f", 0, 1, F)? not very pretty.

I guess you don't want to support varargs?

Sorry could you clarify what you mean by "Supporting all the f/0 to f/3 is difficult."? hard to do in the gojq implementation or hard to write custom functions that behave well?

[itchyny]

I think in most cases you want min/max arg count range? gojq.WithFunction("f", [2]int{0, 1}, F) or gojq.WithFunction("f", 0, 1, F)? not very pretty.

I like the idea of giving both min/max arity. It will cover the use case without duplicating the function implementation with the same name.

Sorry could you clarify what you mean by "Supporting all the f/0 to f/3 is difficult."? hard to do in the gojq implementation or hard to write custom functions that behave well?

I was thinking of overwriting the former definition by the latter when the function name conflicts. But I can implement the case by the same way I used to do within the previous implementation accepting single arity. So user don't need to worry about this (see this test for sample).

Thanks for your valuable feedback, I will merge the branch in a few days.

[wader]

Nice! glad I can help. And thank you for gojq, very useful and i've learned a lot while reading the code.

Did you see my comment about passing along customFuncs to def and modules? #46 (comment)

[itchyny]

Did you see my comment about passing along customFuncs to def and modules?

Yes, I was to push my changes after writing tests.

[wader]

@itchyny 👍

[wader]

@itchyny Thanks!