diff --git a/mk2rbc/variable.go b/mk2rbc/variable.go
new file mode 100644
index 0000000..56db192
--- /dev/null
+++ b/mk2rbc/variable.go
@@ -0,0 +1,300 @@
+// Copyright 2021 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package mk2rbc
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+type variable interface {
+	name() string
+	emitGet(gctx *generationContext, isDefined bool)
+	emitSet(gctx *generationContext, asgn *assignmentNode)
+	emitDefined(gctx *generationContext)
+	valueType() starlarkType
+	defaultValueString() string
+	isPreset() bool
+}
+
+type baseVariable struct {
+	nam    string
+	typ    starlarkType
+	preset bool // true if it has been initialized at startup
+}
+
+func (v baseVariable) name() string {
+	return v.nam
+}
+
+func (v baseVariable) valueType() starlarkType {
+	return v.typ
+}
+
+func (v baseVariable) isPreset() bool {
+	return v.preset
+}
+
+var defaultValuesByType = map[starlarkType]string{
+	starlarkTypeUnknown: `""`,
+	starlarkTypeList:    "[]",
+	starlarkTypeString:  `""`,
+	starlarkTypeInt:     "0",
+	starlarkTypeBool:    "False",
+	starlarkTypeVoid:    "None",
+}
+
+func (v baseVariable) defaultValueString() string {
+	if v, ok := defaultValuesByType[v.valueType()]; ok {
+		return v
+	}
+	panic(fmt.Errorf("%s has unknown type %q", v.name(), v.valueType()))
+}
+
+type productConfigVariable struct {
+	baseVariable
+}
+
+func (pcv productConfigVariable) emitSet(gctx *generationContext, asgn *assignmentNode) {
+	emitAssignment := func() {
+		pcv.emitGet(gctx, true)
+		gctx.write(" = ")
+		asgn.value.emitListVarCopy(gctx)
+	}
+	emitAppend := func() {
+		pcv.emitGet(gctx, true)
+		gctx.write(" += ")
+		if pcv.valueType() == starlarkTypeString {
+			gctx.writef(`" " + `)
+		}
+		asgn.value.emit(gctx)
+	}
+
+	switch asgn.flavor {
+	case asgnSet:
+		emitAssignment()
+	case asgnAppend:
+		emitAppend()
+	case asgnMaybeAppend:
+		// If we are not sure variable has been assigned before, emit setdefault
+		if pcv.typ == starlarkTypeList {
+			gctx.writef("%s(handle, %q)", cfnSetListDefault, pcv.name())
+		} else {
+			gctx.writef("cfg.setdefault(%q, %s)", pcv.name(), pcv.defaultValueString())
+		}
+		gctx.newLine()
+		emitAppend()
+	case asgnMaybeSet:
+		gctx.writef("if cfg.get(%q) == None:", pcv.nam)
+		gctx.indentLevel++
+		gctx.newLine()
+		emitAssignment()
+		gctx.indentLevel--
+	}
+}
+
+func (pcv productConfigVariable) emitGet(gctx *generationContext, isDefined bool) {
+	if isDefined || pcv.isPreset() {
+		gctx.writef("cfg[%q]", pcv.nam)
+	} else {
+		gctx.writef("cfg.get(%q, %s)", pcv.nam, pcv.defaultValueString())
+	}
+}
+
+func (pcv productConfigVariable) emitDefined(gctx *generationContext) {
+	gctx.writef("g.get(%q) != None", pcv.name())
+}
+
+type otherGlobalVariable struct {
+	baseVariable
+}
+
+func (scv otherGlobalVariable) emitSet(gctx *generationContext, asgn *assignmentNode) {
+	emitAssignment := func() {
+		scv.emitGet(gctx, true)
+		gctx.write(" = ")
+		asgn.value.emitListVarCopy(gctx)
+	}
+
+	emitAppend := func() {
+		scv.emitGet(gctx, true)
+		gctx.write(" += ")
+		if scv.valueType() == starlarkTypeString {
+			gctx.writef(`" " + `)
+		}
+		asgn.value.emit(gctx)
+	}
+
+	switch asgn.flavor {
+	case asgnSet:
+		emitAssignment()
+	case asgnAppend:
+		emitAppend()
+	case asgnMaybeAppend:
+		// If we are not sure variable has been assigned before, emit setdefault
+		gctx.writef("g.setdefault(%q, %s)", scv.name(), scv.defaultValueString())
+		gctx.newLine()
+		emitAppend()
+	case asgnMaybeSet:
+		gctx.writef("if g.get(%q) == None:", scv.nam)
+		gctx.indentLevel++
+		gctx.newLine()
+		emitAssignment()
+		gctx.indentLevel--
+	}
+}
+
+func (scv otherGlobalVariable) emitGet(gctx *generationContext, isDefined bool) {
+	if isDefined || scv.isPreset() {
+		gctx.writef("g[%q]", scv.nam)
+	} else {
+		gctx.writef("g.get(%q, %s)", scv.nam, scv.defaultValueString())
+	}
+}
+
+func (scv otherGlobalVariable) emitDefined(gctx *generationContext) {
+	gctx.writef("g.get(%q) != None", scv.name())
+}
+
+type localVariable struct {
+	baseVariable
+}
+
+func (lv localVariable) emitDefined(_ *generationContext) {
+	panic("implement me")
+}
+
+func (lv localVariable) String() string {
+	return "_" + lv.nam
+}
+
+func (lv localVariable) emitSet(gctx *generationContext, asgn *assignmentNode) {
+	switch asgn.flavor {
+	case asgnSet:
+		gctx.writef("%s = ", lv)
+		asgn.value.emitListVarCopy(gctx)
+	case asgnAppend:
+		lv.emitGet(gctx, false)
+		gctx.write(" += ")
+		if lv.valueType() == starlarkTypeString {
+			gctx.writef(`" " + `)
+		}
+		asgn.value.emit(gctx)
+	case asgnMaybeAppend:
+		gctx.writef("%s(%q, ", cfnLocalAppend, lv)
+		asgn.value.emit(gctx)
+		gctx.write(")")
+	case asgnMaybeSet:
+		gctx.writef("%s(%q, ", cfnLocalSetDefault, lv)
+		asgn.value.emit(gctx)
+		gctx.write(")")
+	}
+}
+
+func (lv localVariable) emitGet(gctx *generationContext, _ bool) {
+	gctx.writef("%s", lv)
+}
+
+type predefinedVariable struct {
+	baseVariable
+	value starlarkExpr
+}
+
+func (pv predefinedVariable) emitGet(gctx *generationContext, _ bool) {
+	pv.value.emit(gctx)
+}
+
+func (pv predefinedVariable) emitSet(_ *generationContext, asgn *assignmentNode) {
+	if expectedValue, ok1 := maybeString(pv.value); ok1 {
+		actualValue, ok2 := maybeString(asgn.value)
+		if ok2 {
+			if actualValue == expectedValue {
+				return
+			}
+			fmt.Fprintf(os.Stderr, "cannot set predefined variable %s to %q, its value should be %q",
+				pv.name(), actualValue, expectedValue)
+			return
+		}
+	}
+	panic(fmt.Errorf("cannot set predefined variable %s to %q", pv.name(), asgn.mkValue.Dump()))
+}
+
+func (pv predefinedVariable) emitDefined(gctx *generationContext) {
+	gctx.write("True")
+}
+
+var localProductConfigVariables = map[string]string{
+	"LOCAL_AUDIO_PRODUCT_PACKAGE":         "PRODUCT_PACKAGES",
+	"LOCAL_AUDIO_PRODUCT_COPY_FILES":      "PRODUCT_COPY_FILES",
+	"LOCAL_AUDIO_DEVICE_PACKAGE_OVERLAYS": "DEVICE_PACKAGE_OVERLAYS",
+	"LOCAL_DUMPSTATE_PRODUCT_PACKAGE":     "PRODUCT_PACKAGES",
+	"LOCAL_GATEKEEPER_PRODUCT_PACKAGE":    "PRODUCT_PACKAGES",
+	"LOCAL_HEALTH_PRODUCT_PACKAGE":        "PRODUCT_PACKAGES",
+	"LOCAL_SENSOR_PRODUCT_PACKAGE":        "PRODUCT_PACKAGES",
+	"LOCAL_KEYMASTER_PRODUCT_PACKAGE":     "PRODUCT_PACKAGES",
+	"LOCAL_KEYMINT_PRODUCT_PACKAGE":       "PRODUCT_PACKAGES",
+}
+
+var presetVariables = map[string]bool{
+	"BUILD_ID":                  true,
+	"HOST_ARCH":                 true,
+	"HOST_OS":                   true,
+	"HOST_BUILD_TYPE":           true,
+	"OUT_DIR":                   true,
+	"PLATFORM_VERSION_CODENAME": true,
+	"PLATFORM_VERSION":          true,
+	"TARGET_ARCH":               true,
+	"TARGET_ARCH_VARIANT":       true,
+	"TARGET_BUILD_TYPE":         true,
+	"TARGET_BUILD_VARIANT":      true,
+	"TARGET_PRODUCT":            true,
+}
+
+// addVariable returns a variable with a given name. A variable is
+// added if it does not exist yet.
+func (ctx *parseContext) addVariable(name string) variable {
+	v, found := ctx.variables[name]
+	if !found {
+		_, preset := presetVariables[name]
+		if vi, found := KnownVariables[name]; found {
+			switch vi.class {
+			case VarClassConfig:
+				v = &productConfigVariable{baseVariable{nam: name, typ: vi.valueType, preset: preset}}
+			case VarClassSoong:
+				v = &otherGlobalVariable{baseVariable{nam: name, typ: vi.valueType, preset: preset}}
+			}
+		} else if name == strings.ToLower(name) {
+			// Heuristics: if variable's name is all lowercase, consider it local
+			// string variable.
+			v = &localVariable{baseVariable{nam: name, typ: starlarkTypeString}}
+		} else {
+			vt := starlarkTypeUnknown
+			if strings.HasPrefix(name, "LOCAL_") {
+				// Heuristics: local variables that contribute to corresponding config variables
+				if cfgVarName, found := localProductConfigVariables[name]; found {
+					vi, found2 := KnownVariables[cfgVarName]
+					if !found2 {
+						panic(fmt.Errorf("unknown config variable %s for %s", cfgVarName, name))
+					}
+					vt = vi.valueType
+				}
+			}
+			v = &otherGlobalVariable{baseVariable{nam: name, typ: vt}}
+		}
+		ctx.variables[name] = v
+	}
+	return v
+}