first pass at a "builder" interface

build/context.go

@@ -0,0 +1,65 @@
+package build
+
+import (
+	"errors"
+	"io"
+	"log"
+
+	"github.com/mmcloughlin/avo"
+)
+
+type Context struct {
+	file     *avo.File
+	function *avo.Function
+	errs     []error
+}
+
+func NewContext() *Context {
+	return &Context{
+		file: avo.NewFile(),
+	}
+}
+
+//go:generate avogen -output zinstructions.go build
+
+func (c *Context) TEXT(name string) {
+	c.function = avo.NewFunction(name)
+	c.file.Functions = append(c.file.Functions, c.function)
+}
+
+func (c *Context) Instruction(i avo.Instruction) {
+	if c.function == nil {
+		c.AddErrorMessage("no active function")
+		return
+	}
+	c.function.AddInstruction(i)
+}
+
+func (c *Context) AddError(err error) {
+	c.errs = append(c.errs, err)
+}
+
+func (c *Context) AddErrorMessage(msg string) {
+	c.AddError(errors.New(msg))
+}
+
+func (c *Context) Result() (*avo.File, []error) {
+	return c.file, c.errs
+}
+
+func (c *Context) Generate(wout, werr io.Writer) {
+	diag := log.New(werr, "", 0)
+
+	f, errs := c.Result()
+	if errs != nil {
+		for _, err := range errs {
+			diag.Println(err)
+		}
+		return
+	}
+
+	p := avo.NewGoPrinter(wout)
+	if err := p.Print(f); err != nil {
+		diag.Fatal(err)
+	}
+}

build/global.go

@@ -0,0 +1,9 @@
+package build
+
+import "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) }