Add default router for non-selector inputs

go/router/router.go

@@ -7,11 +7,20 @@ import (
 type Router struct {
 	selectors []string
 	symbols map[string]string
+	navigable bool
 }
 
 func NewRouter() Router {
 	return Router{
 		symbols: make(map[string]string),
+		navigable: true,
+	}
+}
+
+func NewStaticRouter(symbol string) Router {
+	return Router{
+		symbols: map[string]string{"_": symbol},
+		navigable: false,
 	}
 }
 
@@ -32,6 +41,14 @@ func(r *Router) Add(selector string, symbol string) error {
 	return nil
 }
 
+func(r *Router) Get(selector string) string {
+	return r.symbols[selector]
+}
+
+func(r *Router) Default() string {
+	return r.symbols["_"]
+}
+
 func(r *Router) Next() []byte {
 	if len(r.selectors) == 0 {
 		return []byte{}
@@ -67,14 +84,23 @@ func(r *Router) ToBytes() []byte {
 
 func FromBytes(b []byte) Router {
 	rb := NewRouter()
+	navigable := true
 	for len(b) > 0 {
+		var k string
 		l := b[0]
-		k := b[1:1+l]
+		if l == 0 {
-		b = b[1+l:]
+			navigable = false
+		} else {
+			k = string(b[1:1+l])
+			b = b[1+l:]
+		}
 		l = b[0]
-		v := b[1:1+l]
+		v := string(b[1:1+l])
+		if !navigable {
+			return NewStaticRouter(v)
+		}
 		b = b[1+l:]
-		rb.Add(string(k), string(v))
+		rb.Add(k, v)
 	}
 	return rb
 }

go/state/state.go

@@ -12,6 +12,7 @@ type State struct {
 	Cache []map[string]string
 	CacheMap map[string]string
 	ExecPath []string
+	Arg *string
 	Idx uint16
 }
 
@@ -38,6 +39,14 @@ func(st State) WithCacheSize(cacheSize uint32) State {
 	return st
 }
 
+func(st *State) PutArg(input string) {
+	st.Arg = &input
+}
+
+func(st *State) PopArg() string {
+	return *st.Arg
+}
+
 func(st *State) Down(input string) {
 	m := make(map[string]string)
 	st.Cache = append(st.Cache, m)

go/vm/vm.go

@@ -2,22 +2,30 @@ package vm
 
 import (
 	"encoding/binary"
-	"fmt"
 	"context"
+	"fmt"
 	"log"
 
-	"git.defalsify.org/festive/state"
 	"git.defalsify.org/festive/resource"
+	"git.defalsify.org/festive/router"
+	"git.defalsify.org/festive/state"
 )
 
 type Runner func(instruction []byte, st state.State, rs resource.Fetcher, ctx context.Context) (state.State, []byte, error)
 
-func Apply(instruction []byte, st state.State, rs resource.Fetcher, ctx context.Context) (state.State, []byte, error) {
+func Apply(input []byte, instruction []byte, st state.State, rs resource.Fetcher, ctx context.Context) (state.State, []byte, error) {
 	var err error
 	st, instruction, err = Run(instruction, st, rs, ctx)
 	if err != nil {
 		return st, instruction, err
 	}
+	rt := router.FromBytes(instruction)
+	
+	sym := rt.Get(string(input))
+	if sym == "" {
+		sym = rt.Default()
+		st.PutArg(string(input))
+	}
 	return st, instruction, nil
 }