Updated README

docs/examples/extensible.go

@@ -0,0 +1,80 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"github.com/MontFerret/ferret/pkg/compiler"
+	"github.com/MontFerret/ferret/pkg/runtime/core"
+	"github.com/MontFerret/ferret/pkg/runtime/values"
+	"os"
+)
+
+func main() {
+	strs, err := getStrings()
+
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	for _, str := range strs {
+		fmt.Println(str)
+	}
+}
+
+func getStrings() ([]string, error) {
+	// function implements is a type of a function that ferret supports as a runtime function
+	transform := func(ctx context.Context, args ...core.Value) (core.Value, error) {
+		// it's just a helper function which helps to validate a number of passed args
+		err := core.ValidateArgs(args, 1)
+
+		if err != nil {
+			// it's recommended to return built-in None type, instead of nil
+			return values.None, err
+		}
+
+		// this is another helper functions allowing to do type validation
+		err = core.ValidateType(args[0], core.StringType)
+
+		if err != nil {
+			return values.None, err
+		}
+
+		// cast to built-in string type
+		str := args[0].(values.String)
+
+		return str.Concat(values.NewString("_ferret")).ToUpper(), nil
+	}
+
+	query := `
+		FOR el IN ["foo", "bar", "qaz"]
+			// conventionally all functions are registered in upper case
+			RETURN TRANSFORM(el)
+	`
+
+	comp := compiler.New()
+	comp.RegisterFunction("transform", transform)
+
+	program, err := comp.Compile(query)
+
+	if err != nil {
+		return nil, err
+	}
+
+	out, err := program.Run(context.Background())
+
+	if err != nil {
+		return nil, err
+	}
+
+	res := make([]string, 0, 3)
+
+	err = json.Unmarshal(out, &res)
+
+	if err != nil {
+		return nil, err
+	}
+
+	return res, nil
+}