compiler: manage variables in a separate varScope struct

Abstract var scope management from the funcScope.

pkg/compiler/vars.go

@@ -0,0 +1,63 @@
+package compiler
+
+type varScope struct {
+	localsCnt int
+	argCnt    int
+	arguments map[string]int
+	locals    []map[string]int
+}
+
+func newVarScope() varScope {
+	return varScope{
+		arguments: make(map[string]int),
+	}
+}
+
+func (c *varScope) newScope() {
+	c.locals = append(c.locals, map[string]int{})
+}
+
+func (c *varScope) dropScope() {
+	c.locals = c.locals[:len(c.locals)-1]
+}
+
+func (c *varScope) getVarIndex(name string) (varType, int) {
+	for i := len(c.locals) - 1; i >= 0; i-- {
+		if i, ok := c.locals[i][name]; ok {
+			return varLocal, i
+		}
+	}
+	if i, ok := c.arguments[name]; ok {
+		return varArgument, i
+	}
+	return 0, -1
+}
+
+// newVariable creates a new local variable or argument in the scope of the function.
+func (c *varScope) newVariable(t varType, name string) int {
+	var n int
+	switch t {
+	case varLocal:
+		return c.newLocal(name)
+	case varArgument:
+		_, ok := c.arguments[name]
+		if ok {
+			panic("argument is already allocated")
+		}
+		n = len(c.arguments)
+		c.arguments[name] = n
+	default:
+		panic("invalid type")
+	}
+	return n
+}
+
+// newLocal creates a new local variable in the current scope.
+func (c *varScope) newLocal(name string) int {
+	idx := len(c.locals) - 1
+	m := c.locals[idx]
+	m[name] = c.localsCnt
+	c.localsCnt++
+	c.locals[idx] = m
+	return c.localsCnt - 1
+}