[gnome-calculator] GCalc: null parameter adds $ prefix to its name

[Daniel Espinosa Ortiz <despinosa src gnome org>]

commit bc68389200aaba41137ac3dee3d4ae53c52b3f38
Author: Daniel Espinosa <esodan gmail com>
Date:   Mon Nov 4 12:59:10 2019 -0600

    GCalc: null parameter adds $ prefix to its name
    
    If a parameter's value is null, its string representation
    return its name with a '$' prefix, in order to identify
    a parameter and no a variable in a math expression

 gcalc/gcalc-parameter.vala     | 2 +-
 tests/gcalc-parsing.vala       | 2 +-
 tests/gcalc-solving-basic.vala | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/gcalc/gcalc-parameter.vala b/gcalc/gcalc-parameter.vala
index a95eaf10..9a17f76e 100644
--- a/gcalc/gcalc-parameter.vala
+++ b/gcalc/gcalc-parameter.vala
@@ -56,7 +56,7 @@ public class GCalc.Parameter : GCalc.Variable, MathParameter {
   // Expression
   internal override string to_string () {
     if (@value == null) {
-      return name;
+      return "$"+name;
     }
     return @value.to_string ();
   }
diff --git a/tests/gcalc-parsing.vala b/tests/gcalc-parsing.vala
index b102ac48..19294c4f 100644
--- a/tests/gcalc-parsing.vala
+++ b/tests/gcalc-parsing.vala
@@ -1138,7 +1138,7 @@ class Tests {
         var v2 = t2.expressions.get_item (0) as MathVariable;
         assert (v2 != null);
         message (eq.to_string ());
-        assert (eq.to_string () == "x=param1");
+        assert (eq.to_string () == "x=$param1");
         p.set_value (10.0);
         message (eq.to_string ());
         assert (eq.to_string () == "x=10");
diff --git a/tests/gcalc-solving-basic.vala b/tests/gcalc-solving-basic.vala
index 73c7d08b..3b8b9a3a 100644
--- a/tests/gcalc-solving-basic.vala
+++ b/tests/gcalc-solving-basic.vala
@@ -1594,7 +1594,7 @@ class Tests {
         assert (p != null);
         assert (p is MathParameter);
         message ("Param without value to string: %s", p.to_string ());
-        assert (p.to_string () == "p");
+        assert (p.to_string () == "$p");
         p.set_value (3.0);
         message ("Param with value to string: %s", p.to_string ());
         assert (p.to_string () == "3");
@@ -1610,7 +1610,7 @@ class Tests {
         assert (c2.@value () == 9.0);
         p.set_value (null);
         message ("Param without value to string: %s", p.to_string ());
-        assert (p.to_string () == "p");
+        assert (p.to_string () == "$p");
         var res3 = eq.solve ();
         if (res3 is ErrorResult) {
           warning ("Error: %s", (res3 as ErrorResult).message);