1 files changed, 70 insertions, 3 deletions

diff --git a/main/command.go b/main/command.go
index 6d75974..04ac7f6 100644
--- a/main/command.go
+++ b/main/command.go
@@ -27,11 +27,18 @@ func (cmd PrintValueCommand) String() string {
 
 type NextCommand struct {}
 func (cmd NextCommand) exec(state *ProgramState) {
-	nextItem, err := state.in.Read()
+	nextItem, err := state.Read()
 	if err != nil {
 		panic("Missing next value")
 	}
+
+	state.prevStart = nextItem.PrevStart
+	state.start = nextItem.Start
+	state.end = nextItem.End
+	state.nextEnd = nextItem.NextEnd
+
 	state.value = []walk.Value{nextItem.Value}
+
 	state.pc++
 }
 func (cmd NextCommand) String() string {
@@ -40,7 +47,7 @@ func (cmd NextCommand) String() string {
 
 type AppendNextCommand struct {}
 func (cmd AppendNextCommand) exec(state *ProgramState) {
-	nextItem, err := state.in.Read()
+	nextItem, err := state.Read()
 	if err != nil {
 		panic("Missing next value")
 	}
@@ -58,9 +65,61 @@ func (cmd AppendNextCommand) String() string {
 	return "N"
 }
 
+type SubstituteNextCommand struct {
+	subex subex.Transducer
+}
+func (cmd SubstituteNextCommand) exec(state *ProgramState) {
+	item, err := state.Peek()
+	if err != nil {
+		panic("Missing next value")
+	}
+
+	newValue, notOk := runSubex(cmd.subex, []walk.Value{item.Value})
+
+	if notOk {
+		state.pc++
+	} else {
+		state.prevStart = item.PrevStart
+		state.start = item.Start
+		state.end = item.End
+		state.nextEnd = item.NextEnd
+		state.pc += 2
+		state.value = newValue
+	}
+}
+func (cmd SubstituteNextCommand) String() string {
+	return "n/.../"
+}
+
+type SubstituteAppendNextCommand struct {
+	subex subex.Transducer
+}
+func (cmd SubstituteAppendNextCommand) exec(state *ProgramState) {
+	item, err := state.Peek()
+	if err != nil {
+		panic("Missing next value")
+	}
+
+	newValue, notOk := runSubex(cmd.subex, []walk.Value{item.Value})
+
+	if notOk {
+		state.pc++
+	} else {
+		state.prevStart = item.PrevStart
+		state.start = item.Start
+		state.end = item.End
+		state.nextEnd = item.NextEnd
+		state.pc += 2
+		state.value = append(state.value, newValue...)
+	}
+}
+func (cmd SubstituteAppendNextCommand) String() string {
+	return "N/.../"
+}
+
 type MergeCommand struct {}
 func (cmd MergeCommand) exec(state *ProgramState) {
-	nextItem, err := state.in.Read()
+	nextItem, err := state.Read()
 	if err != nil {
 		panic("Missing next value")
 	}
@@ -85,6 +144,14 @@ func (cmd MergeCommand) String() string {
 	return "m"
 }
 
+type FullMergeCommand struct {}
+func (cmd FullMergeCommand) exec(state *ProgramState) {
+	panic("Unimplemented")
+}
+func (cmd FullMergeCommand) String() string {
+	return "M"
+}
+
 type DeleteValueCommand struct {}
 func (cmd DeleteValueCommand) exec(state *ProgramState) {
 	state.value = nil