Calling Functions from Go

After compiling a script, the Go host can call any named function with compiled.Call. Arguments are converted from Go types automatically; return values come back as *tengo.Variable with typed accessors: .Int(), .String(), .Float(), .Bool(), and .Map(). compiled.CanCall(name) checks that a name is defined and callable before dispatching.

fmt := import("fmt")

Functions at script scope are directly callable from Go by name. No export keyword or registration needed.

add := func(a, b) { return a + b }

clamp := func(v, lo, hi) {
    if v < lo { return lo }
    if v > hi { return hi }
    return v
}

greet := func(name, lang) {
    phrases := {en: "Hello", sv: "Hej", es: "Hola", fr: "Bonjour"}
    p := phrases[lang]
    if is_undefined(p) { p = "Hello" }
    return p + ", " + name + "!"
}

score_band returns a map; on the Go side read it with .Map().

score_band := func(score) {
    if score >= 90 { return {grade: "A", pass: true} }
    if score >= 75 { return {grade: "B", pass: true} }
    if score >= 60 { return {grade: "C", pass: true} }
    return {grade: "F", pass: false}
}

Standalone demo — same calls the Go host makes; produces identical output.

fmt.println(add(3, 4))
fmt.println(clamp(150, 0, 100))
fmt.println(greet("Alice", "sv"))
band := score_band(82)
fmt.printf("%s (pass=%v)\n", band.grade, band.pass)

Go host

package main

import (
	"fmt"
	"log"

	tengo "github.com/tengolang/tengo/v3"
)

const script = `
add := func(a, b) { return a + b }

clamp := func(v, lo, hi) {
    if v < lo { return lo }
    if v > hi { return hi }
    return v
}

greet := func(name, lang) {
    phrases := {en: "Hello", sv: "Hej", es: "Hola", fr: "Bonjour"}
    p := phrases[lang]
    if is_undefined(p) { p = "Hello" }
    return p + ", " + name + "!"
}

score_band := func(score) {
    if score >= 90 { return {grade: "A", pass: true} }
    if score >= 75 { return {grade: "B", pass: true} }
    if score >= 60 { return {grade: "C", pass: true} }
    return {grade: "F", pass: false}
}
`

func main() {
	compiled, err := tengo.NewScript([]byte(script)).Run()
	if err != nil {
		log.Fatal(err)
	}

	res, _ := compiled.Call("add", 3, 4)
	fmt.Println(res.Int()) // 7

	res, _ = compiled.Call("clamp", 150, 0, 100)
	fmt.Println(res.Int()) // 100

	res, _ = compiled.Call("greet", "Alice", "sv")
	fmt.Println(res.String()) // Hej, Alice!

	// CanCall guards against user scripts that omit a function.
	if compiled.CanCall("score_band") {
		res, _ = compiled.Call("score_band", 82)
		m := res.Map()
		fmt.Printf("%s (pass=%v)\n", m["grade"], m["pass"]) // B (pass=true)
	}
}

try it

7
100
Hej, Alice!
B (pass=true)
loading…

by tengolang/tengo v3 | source