From fb484bf941d400596af5b4a84cdaa6a9e903425f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C3=A9a=20Saviot?= <lea.saviot@numworks.com>
Date: Fri, 9 Nov 2018 16:48:52 +0100
Subject: [PATCH] [poincare] More elegant prevention of parsing "3=4>x" and
 "4<x=3"

---
 poincare/src/parsing/parser.cpp | 8 +++-----
 poincare/src/parsing/token.h    | 7 ++++++-
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/poincare/src/parsing/parser.cpp b/poincare/src/parsing/parser.cpp
index 2225a194f..26115d313 100644
--- a/poincare/src/parsing/parser.cpp
+++ b/poincare/src/parsing/parser.cpp
@@ -15,8 +15,8 @@ Expression Parser::parseUntil(Token::Type stoppingType) {
   typedef void (Parser::*TokenParser)(Expression & leftHandSide);
   static constexpr TokenParser tokenParsers[] = {
     &Parser::parseUnexpected,      // Token::EndOfStream
-    &Parser::parseEqual,           // Token::Equal
     &Parser::parseStore,           // Token::Store
+    &Parser::parseEqual,           // Token::Equal
     &Parser::parseUnexpected,      // Token::RightBracket
     &Parser::parseUnexpected,      // Token::RightParenthesis
     &Parser::parseUnexpected,      // Token::RightBrace
@@ -170,10 +170,8 @@ void Parser::parseEqual(Expression & leftHandSide) {
   }
   Expression rightHandSide;
   if (parseBinaryOperator(leftHandSide, rightHandSide, Token::Equal)) {
-    if (rightHandSide.type() == ExpressionNode::Type::Store) {
-      m_status = Status::Error; // Equal cannot have a Store on the right
-      return;
-    }
+    /* We parse until finding a token of lesser precedence than Equal. The next
+     * token is thus either EndOfStream or Store. */
     leftHandSide = Equal(leftHandSide, rightHandSide);
   }
   if (!m_nextToken.is(Token::EndOfStream)) {
diff --git a/poincare/src/parsing/token.h b/poincare/src/parsing/token.h
index 87b8766d5..e10740685 100644
--- a/poincare/src/parsing/token.h
+++ b/poincare/src/parsing/token.h
@@ -17,8 +17,13 @@ public:
   enum Type {
     // Ordered from lower to higher precedence to make Parser's job easier
     EndOfStream = 0, // Must be the first
-    Equal,
     Store,
+    Equal,
+      /* Equal should have a higher precedence than Store, because
+       * Tokenizer::parseEqual looks for a right hand side until it finds a
+       * token of lesser precedence than Equal, and this prevents expressions
+       * such as "3=4>a". Tokenizer::parseStore uses a special algorithm that
+       * prevents (3>4=a). */
     RightBracket,
     RightParenthesis,
     RightBrace,