Add range loops to entity

entity/expression.go

@@ -467,6 +467,41 @@ func (this *Loop) String () string {
 	return fmt.Sprint("loop ", this.Body)
 }
 
+var _ Expression = &For { }
+// For is a special kind of loop that evaluates an expression for each element
+// of an array or slice. It accepts an index declaration and an element
+// declaration, which are scoped to the loop's body and are set to the index of
+// the current element and the element itself respectively at the beginning of
+// each iteration. The assignment rules of a for statement are identical to that
+// of a normal loop.
+type For struct {
+	// Syntax
+	Pos     errors.Position
+	Index   Expression
+	Element Expression
+	Over    Expression
+	Body    Expression
+
+	// Semantics
+	Ty Type
+}
+func (*For) expression(){}
+func (this *For) Position () errors.Position { return this.Pos }
+func (this *For) Type () Type { return this.Ty }
+func (this *For) HasExplicitType () bool {
+	// this is as accurate as possible without doing a full analysis of the
+	// loop
+	return false
+}
+func (this *For) String () string {
+	out := "for"
+	if this.Index != nil {
+		out += " " + this.Index.String()
+	}
+	out += fmt.Sprint(" %v in %v %v", this.Element, this.Over, this.Body)
+	return out
+}
+
 var _ Expression = &Break { }
 // Break allows breaking out of loops. It has no value and may not be assigned
 // to anything. It is never a valid location expression.