diff --git a/tracker/alert.go b/tracker/alert.go
index 5986967..871e828 100644
--- a/tracker/alert.go
+++ b/tracker/alert.go
@@ -18,7 +18,7 @@ type (
 	}
 
 	AlertPriority  int
-	AlertYieldFunc func(alert Alert)
+	AlertYieldFunc func(index int, alert Alert) bool
 	Alerts         Model
 )
 
@@ -35,9 +35,13 @@ func (m *Model) Alerts() *Alerts { return (*Alerts)(m) }
 
 // Alerts methods
 
-func (m *Alerts) Iterate(yield AlertYieldFunc) {
-	for _, a := range m.alerts {
-		yield(a)
+func (m *Alerts) Iterate() func(yield func(index int, alert Alert) bool) {
+	return func(yield func(index int, alert Alert) bool) {
+		for i, a := range m.alerts {
+			if !yield(i, a) {
+				break
+			}
+		}
 	}
 }
 
diff --git a/tracker/gioui/instrument_editor.go b/tracker/gioui/instrument_editor.go
index 1b7d67d..5128ae7 100644
--- a/tracker/gioui/instrument_editor.go
+++ b/tracker/gioui/instrument_editor.go
@@ -338,13 +338,13 @@ func (ie *InstrumentEditor) layoutUnitList(gtx C, t *Tracker) D {
 	addUnitBtnStyle.IconButtonStyle.Background = t.Theme.Fg
 	addUnitBtnStyle.IconButtonStyle.Inset = layout.UniformInset(unit.Dp(4))
 
-	index := 0
 	var units [256]tracker.UnitListItem
-	(*tracker.Units)(t.Model).Iterate(func(item tracker.UnitListItem) (ok bool) {
-		units[index] = item
-		index++
-		return index <= 256
-	})
+	for i, item := range (*tracker.Units)(t.Model).Iterate() {
+		if i >= 256 {
+			break
+		}
+		units[i] = item
+	}
 	count := intMin(ie.unitDragList.TrackerList.Count(), 256)
 
 	element := func(gtx C, i int) D {
diff --git a/tracker/gioui/popup_alert.go b/tracker/gioui/popup_alert.go
index 6ffcfb6..c44a5db 100644
--- a/tracker/gioui/popup_alert.go
+++ b/tracker/gioui/popup_alert.go
@@ -36,7 +36,7 @@ func (a *PopupAlert) Layout(gtx C) D {
 	a.prevUpdate = now
 
 	var totalY float64 = float64(gtx.Dp(38))
-	a.alerts.Iterate(func(alert tracker.Alert) {
+	for _, alert := range a.alerts.Iterate() {
 		var color, textColor, shadeColor color.NRGBA
 		switch alert.Priority {
 		case tracker.Warning:
@@ -76,6 +76,6 @@ func (a *PopupAlert) Layout(gtx C) D {
 				return dims
 			})
 		})
-	})
+	}
 	return D{}
 }
diff --git a/tracker/gioui/unit_editor.go b/tracker/gioui/unit_editor.go
index 0c2543b..7f33a2d 100644
--- a/tracker/gioui/unit_editor.go
+++ b/tracker/gioui/unit_editor.go
@@ -102,11 +102,10 @@ func (pe *UnitEditor) layoutSliders(gtx C, t *Tracker) D {
 	}
 
 	index := 0
-	t.Model.Params().Iterate(func(param tracker.Parameter) {
+	for param := range t.Model.Params().Iterate() {
 		pe.Parameters[index].Parameter = param
 		index++
-	})
-
+	}
 	element := func(gtx C, index int) D {
 		if index < 0 || index >= numItems {
 			return D{}
@@ -177,12 +176,12 @@ func (pe *UnitEditor) layoutFooter(gtx C, t *Tracker) D {
 
 func (pe *UnitEditor) layoutUnitTypeChooser(gtx C, t *Tracker) D {
 	var names [256]string
-	index := 0
-	t.Model.SearchResults().Iterate(func(item string) (ok bool) {
-		names[index] = item
-		index++
-		return index <= 256
-	})
+	for i, item := range t.Model.SearchResults().Iterate() {
+		if i >= 256 {
+			break
+		}
+		names[i] = item
+	}
 	element := func(gtx C, i int) D {
 		w := LabelStyle{Text: names[i], ShadeColor: black, Color: white, Font: labelDefaultFont, FontSize: unit.Sp(12), Shaper: t.Theme.Shaper}
 		if i == pe.searchList.TrackerList.Selected() {
diff --git a/tracker/list.go b/tracker/list.go
index 8ba5731..c86d4df 100644
--- a/tracker/list.go
+++ b/tracker/list.go
@@ -38,8 +38,8 @@ type (
 		StackNeed, StackBefore, StackAfter int
 	}
 
-	UnitYieldFunc       func(item UnitListItem) (ok bool)
-	UnitSearchYieldFunc func(item string) (ok bool)
+	UnitYieldFunc       func(index int, item UnitListItem) (ok bool)
+	UnitSearchYieldFunc func(index int, item string) (ok bool)
 
 	Instruments   Model // Instruments is a list of instruments, implementing ListData & MutableListData interfaces
 	Units         Model // Units is a list of all the units in the selected instrument, implementing ListData & MutableListData interfaces
@@ -323,24 +323,26 @@ func (m *Units) SetSelectedType(t string) {
 	m.d.Song.Patch[m.d.InstrIndex].Units[m.d.UnitIndex].ID = oldUnit.ID // keep the ID of the replaced unit
 }
 
-func (v *Units) Iterate(yield UnitYieldFunc) {
-	if v.d.InstrIndex < 0 || v.d.InstrIndex >= len(v.d.Song.Patch) {
-		return
-	}
-	stackBefore := 0
-	for _, unit := range v.d.Song.Patch[v.d.InstrIndex].Units {
-		stackAfter := stackBefore + unit.StackChange()
-		if !yield(UnitListItem{
-			Type:        unit.Type,
-			Comment:     unit.Comment,
-			Disabled:    unit.Disabled,
-			StackNeed:   unit.StackNeed(),
-			StackBefore: stackBefore,
-			StackAfter:  stackAfter,
-		}) {
-			break
+func (v *Units) Iterate() func(yield UnitYieldFunc) {
+	return func(yield UnitYieldFunc) {
+		if v.d.InstrIndex < 0 || v.d.InstrIndex >= len(v.d.Song.Patch) {
+			return
+		}
+		stackBefore := 0
+		for i, unit := range v.d.Song.Patch[v.d.InstrIndex].Units {
+			stackAfter := stackBefore + unit.StackChange()
+			if !yield(i, UnitListItem{
+				Type:        unit.Type,
+				Comment:     unit.Comment,
+				Disabled:    unit.Disabled,
+				StackNeed:   unit.StackNeed(),
+				StackBefore: stackBefore,
+				StackAfter:  stackAfter,
+			}) {
+				break
+			}
+			stackBefore = stackAfter
 		}
-		stackBefore = stackAfter
 	}
 }
 
@@ -743,13 +745,17 @@ func (v *SearchResults) List() List {
 	return List{v}
 }
 
-func (l *SearchResults) Iterate(yield UnitSearchYieldFunc) {
-	for _, name := range sointu.UnitNames {
-		if !strings.HasPrefix(name, l.d.UnitSearchString) {
-			continue
-		}
-		if !yield(name) {
-			break
+func (l *SearchResults) Iterate() func(yield UnitSearchYieldFunc) {
+	return func(yield UnitSearchYieldFunc) {
+		index := 0
+		for _, name := range sointu.UnitNames {
+			if !strings.HasPrefix(name, l.d.UnitSearchString) {
+				continue
+			}
+			if !yield(index, name) {
+				break
+			}
+			index++
 		}
 	}
 }
diff --git a/tracker/model_test.go b/tracker/model_test.go
index b77b860..36ef169 100644
--- a/tracker/model_test.go
+++ b/tracker/model_test.go
@@ -292,14 +292,14 @@ func FuzzModel(f *testing.F) {
 				index--
 				return index > 0
 			}, seed)
-			state.model.Alerts().Iterate(func(a tracker.Alert) {
+			for _, a := range model.Alerts().Iterate() {
 				if a.Name == "IDCollision" {
 					t.Errorf("Path: %s Model has ID collisions", totalPath)
 				}
 				if a.Name == "InvalidUnitParameters" {
 					t.Errorf("Path: %s Model units with invalid parameters", totalPath)
 				}
-			})
+			}
 		}
 		closeChan <- struct{}{}
 	})
diff --git a/tracker/params.go b/tracker/params.go
index 3e09f99..afbf3df 100644
--- a/tracker/params.go
+++ b/tracker/params.go
@@ -41,7 +41,7 @@ type (
 
 	Params Model
 
-	ParamYieldFunc func(Parameter)
+	ParamYieldFunc func(param Parameter) bool
 
 	ParameterType int
 )
@@ -77,59 +77,71 @@ func (pl *Params) change(n string, severity ChangeSeverity) func() {
 
 func (pl *Params) Count() int {
 	count := 0
-	pl.Iterate(func(p Parameter) {
+	for range pl.Iterate() {
 		count++
-	})
+	}
 	return count
 }
 
 func (pl *Params) SelectedItem() (ret Parameter) {
 	index := pl.Selected()
-	pl.Iterate(func(param Parameter) {
+	for param := range pl.Iterate() {
 		if index == 0 {
 			ret = param
 		}
 		index--
-	})
+	}
 	return
 }
 
-func (pl *Params) Iterate(yield ParamYieldFunc) {
-	if pl.d.InstrIndex < 0 || pl.d.InstrIndex >= len(pl.d.Song.Patch) {
-		return
-	}
-	if pl.d.UnitIndex < 0 || pl.d.UnitIndex >= len(pl.d.Song.Patch[pl.d.InstrIndex].Units) {
-		return
-	}
-	unit := &pl.d.Song.Patch[pl.d.InstrIndex].Units[pl.d.UnitIndex]
-	unitType, ok := sointu.UnitTypes[unit.Type]
-	if !ok {
-		return
-	}
-	for i := range unitType {
-		if !unitType[i].CanSet {
-			continue
+func (pl *Params) Iterate() func(yield ParamYieldFunc) {
+	return func(yield ParamYieldFunc) {
+		if pl.d.InstrIndex < 0 || pl.d.InstrIndex >= len(pl.d.Song.Patch) {
+			return
 		}
-		if unit.Type == "oscillator" && unit.Parameters["type"] != sointu.Sample && i >= 11 {
-			break // don't show the sample related params unless necessary
+		if pl.d.UnitIndex < 0 || pl.d.UnitIndex >= len(pl.d.Song.Patch[pl.d.InstrIndex].Units) {
+			return
 		}
-		yield(NamedParameter{
-			parameter: parameter{m: (*Model)(pl), unit: unit},
-			up:        &unitType[i],
-		})
-	}
-	if unit.Type == "oscillator" && unit.Parameters["type"] == sointu.Sample {
-		yield(GmDlsEntryParameter{parameter: parameter{m: (*Model)(pl), unit: unit}})
-	}
-	switch {
-	case unit.Type == "delay":
-		if unit.Parameters["stereo"] == 1 && len(unit.VarArgs)%2 == 1 {
-			unit.VarArgs = append(unit.VarArgs, 1)
+		unit := &pl.d.Song.Patch[pl.d.InstrIndex].Units[pl.d.UnitIndex]
+		unitType, ok := sointu.UnitTypes[unit.Type]
+		if !ok {
+			return
 		}
-		yield(ReverbParameter{parameter: parameter{m: (*Model)(pl), unit: unit}})
-		yield(DelayLinesParameter{parameter: parameter{m: (*Model)(pl), unit: unit}})
-		for i := range unit.VarArgs {
-			yield(DelayTimeParameter{parameter: parameter{m: (*Model)(pl), unit: unit}, index: i})
+		for i := range unitType {
+			if !unitType[i].CanSet {
+				continue
+			}
+			if unit.Type == "oscillator" && unit.Parameters["type"] != sointu.Sample && i >= 11 {
+				break // don't show the sample related params unless necessary
+			}
+			if !yield(NamedParameter{
+				parameter: parameter{m: (*Model)(pl), unit: unit},
+				up:        &unitType[i],
+			}) {
+				return
+			}
+		}
+		if unit.Type == "oscillator" && unit.Parameters["type"] == sointu.Sample {
+			if !yield(GmDlsEntryParameter{parameter: parameter{m: (*Model)(pl), unit: unit}}) {
+				return
+			}
+		}
+		switch {
+		case unit.Type == "delay":
+			if unit.Parameters["stereo"] == 1 && len(unit.VarArgs)%2 == 1 {
+				unit.VarArgs = append(unit.VarArgs, 1)
+			}
+			if !yield(ReverbParameter{parameter: parameter{m: (*Model)(pl), unit: unit}}) {
+				return
+			}
+			if !yield(DelayLinesParameter{parameter: parameter{m: (*Model)(pl), unit: unit}}) {
+				return
+			}
+			for i := range unit.VarArgs {
+				if !yield(DelayTimeParameter{parameter: parameter{m: (*Model)(pl), unit: unit}, index: i}) {
+					return
+				}
+			}
 		}
 	}
 }