Factor out engine loop code

go/dev/interactive.go

@@ -1,12 +1,9 @@
 package main
 
 import (
-	"bufio"
-	"bytes"
 	"context"
 	"flag"
 	"fmt"
-	"strings"
 	"os"
 
 	"git.defalsify.org/festive/engine"
@@ -22,32 +19,9 @@ func main() {
 
 	ctx := context.Background()
 	en := engine.NewDefaultEngine(dir)
-	err := en.Init(root, ctx)
+	err := engine.Loop(root, &en, ctx)
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "cannot init: %v\n", err)
+		fmt.Fprintf(os.Stderr, "loop exited with error: %v", err)
 		os.Exit(1)
 	}
-
-	b := bytes.NewBuffer(nil)
-	en.WriteResult(b)
-	fmt.Println(b.String())
-
-	running := true
-	for running {
-		reader := bufio.NewReader(os.Stdin)
-		in, err := reader.ReadString('\n')
-		if err != nil {
-			fmt.Fprintf(os.Stderr, "cannot read input: %v\n", err)
-			os.Exit(1)
-		}
-		in = strings.TrimSpace(in)
-		running, err = en.Exec([]byte(in), ctx)
-		if err != nil {
-			fmt.Fprintf(os.Stderr, "unexpected termination: %v\n", err)
-			os.Exit(1)
-		}
-		b := bytes.NewBuffer(nil)
-		en.WriteResult(b)
-		fmt.Println(b.String())
-	}
 }

go/engine/loop.go

@@ -0,0 +1,39 @@
+package engine
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"strings"
+)
+
+func Loop(startSym string, en *Engine, ctx context.Context) error {
+	err := en.Init(startSym, ctx)
+	if err != nil {
+		return fmt.Errorf("cannot init: %v\n", err)
+	}
+
+	b := bytes.NewBuffer(nil)
+	en.WriteResult(b)
+	fmt.Println(b.String())
+
+	running := true
+	for running {
+		reader := bufio.NewReader(os.Stdin)
+		in, err := reader.ReadString('\n')
+		if err != nil {
+			return fmt.Errorf("cannot read input: %v\n", err)
+		}
+		in = strings.TrimSpace(in)
+		running, err = en.Exec([]byte(in), ctx)
+		if err != nil {
+			return fmt.Errorf("unexpected termination: %v\n", err)
+		}
+		b := bytes.NewBuffer(nil)
+		en.WriteResult(b)
+		fmt.Println(b.String())
+	}
+	return nil
+}