[poincare] Implement isPositive for symbols Pi and e

Change-Id: I6fb3f605eaf62848b2e90b186c9adb00b330f91d

poincare/include/poincare/symbol.h

@@ -34,6 +34,7 @@ public:
   char name() const;
   Type type() const override;
   Expression * clone() const override;
+  bool isPositive() const override;
   bool isMatrixSymbol() const;
 private:
   Evaluation<float> * privateEvaluate(SinglePrecision p, Context& context, AngleUnit angleUnit) const override { return templatedEvaluate<float>(context, angleUnit); }

poincare/src/symbol.cpp

@@ -4,6 +4,7 @@
 #include "layout/baseline_relative_layout.h"
 #include "layout/string_layout.h"
 #include <poincare/complex_matrix.h>
+#include <ion.h>
 extern "C" {
 #include <assert.h>
 }
@@ -53,6 +54,21 @@ Expression * Symbol::clone() const {
   return new Symbol(m_name);
 }
 
+bool Symbol::isPositive() const {
+  /* TODO: Maybe, we will want to know that from a context given in parameter:
+  if (context.expressionForSymbol(this) != nullptr) {
+    return context.expressionForSymbol(this)->isPositive(context);
+  }
+  return false;*/
+  if (m_name == Ion::Charset::SmallPi) {
+    return true;
+  }
+  if (m_name == Ion::Charset::Exponential) {
+    return true;
+  }
+  return false;
+}
+
 template<typename T>
 Evaluation<T> * Symbol::templatedEvaluate(Context& context, AngleUnit angleUnit) const {
   if (context.expressionForSymbol(this) != nullptr) {