some command line flags for builders

build/context.go

@@ -20,9 +20,7 @@ func NewContext() *Context {
 	}
 }
 
-//go:generate avogen -output zinstructions.go build
-
-func (c *Context) TEXT(name string) {
+func (c *Context) Function(name string) {
 	c.function = avo.NewFunction(name)
 	c.file.Functions = append(c.file.Functions, c.function)
 }
@@ -35,6 +33,8 @@ func (c *Context) Instruction(i avo.Instruction) {
 	c.function.AddInstruction(i)
 }
 
+//go:generate avogen -output zinstructions.go build
+
 func (c *Context) AddError(err error) {
 	c.errs = append(c.errs, err)
 }

build/global.go

@@ -1,9 +1,35 @@
 package build
 
-import "os"
+import (
+	"flag"
+	"io"
+	"log"
+	"os"
+)
 
 // ctx provides a global build context.
 var ctx = NewContext()
 
-func TEXT(name string) { ctx.TEXT(name) }
-func EOF()             { ctx.Generate(os.Stdout, os.Stderr) }
+func TEXT(name string) { ctx.Function(name) }
+
+var (
+	output = flag.String("output", "", "output filename (default stdout)")
+)
+
+func EOF() {
+	if !flag.Parsed() {
+		flag.Parse()
+	}
+
+	var w io.Writer = os.Stdout
+	if *output != "" {
+		if f, err := os.Create(*output); err != nil {
+			log.Fatal(err)
+		} else {
+			defer f.Close()
+			w = f
+		}
+	}
+
+	ctx.Generate(w, os.Stderr)
+}