Add substitute next commands

1 files changed, 19 insertions, 1 deletions

diff --git a/main/main.go b/main/main.go
index 3fb1cbf..47bcddb 100644
--- a/main/main.go
+++ b/main/main.go
@@ -11,11 +11,29 @@ import (
 type ProgramState struct {
 	value, xreg, yreg, zreg []walk.Value
 	start, prevStart, end, nextEnd bool
+	// TODO: This will only ever have 0 or 1 values, it is a slice out of laziness
+	peekStack []walk.WalkItem
 	in walk.StredReader
 	out walk.StredWriter
 	program []Command
 	pc int
 }
+func (state *ProgramState) Read() (walk.WalkItem, error) {
+	if len(state.peekStack) > 0 {
+		item := state.peekStack[len(state.peekStack) - 1]
+		state.peekStack = state.peekStack[:len(state.peekStack) - 1]
+		return item, nil
+	}
+	return state.in.Read()
+}
+func (state *ProgramState) Peek() (walk.WalkItem, error) {
+	item, err := state.Read()
+	if err != nil {
+		return walk.WalkItem{}, err
+	}
+	state.peekStack = append(state.peekStack, item)
+	return item, nil
+}
 
 type config struct {
 	quiet bool
@@ -38,7 +56,7 @@ func run(config config) {
 	}
 
 	for {
-		walkItem, err := state.in.Read()
+		walkItem, err := state.Read()
 		if err != nil {
 			break
 		}