operator-post-inc.go: new post int decrement operator '--'

operator-post-inc.go

@@ -35,7 +35,39 @@ func evalPostInc(ctx ExprContext, opTerm *term) (v any, err error) {
 	return
 }
 
+// -------- post decrement term
+
+func newPostDecTerm(tk *Token) *term {
+	return &term{
+		tk:       *tk,
+		parent:   nil,
+		children: make([]*term, 0, 1),
+		position: posPostfix,
+		priority: priIncDec,
+		evalFunc: evalPostDec,
+	}
+}
+
+func evalPostDec(ctx ExprContext, opTerm *term) (v any, err error) {
+	var childValue any
+	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
+		return
+	}
+
+	/* if it, ok := childValue.(Iterator); ok {
+		v, err = it.Next()
+	} else  */if IsInteger(childValue) && opTerm.children[0].symbol() == SymVariable {
+		v = childValue
+		i, _ := childValue.(int64)
+		ctx.SetVar(opTerm.children[0].source(), i-1)
+	} else {
+		err = opTerm.errIncompatibleType(childValue)
+	}
+	return
+}
+
 // init
 func init() {
 	registerTermConstructor(SymDoublePlus, newPostIncTerm)
+	registerTermConstructor(SymDoubleMinus, newPostDecTerm)
 }