===================================================================
CPW Part 16 (A): Equality and Relational Expressions in the Grammar	[TOC]
===================================================================

The new operators "``==``", "``!=``", "``>``", "``>=``", "``<``" and "``<=``"
should habe the same meaning, associativity and precedence as in C (See
__Session 8, Page 4__). Below the corresponding grammar. Note that some of the
production rules were simply renamed (e.g. _expr_ into _additive-expr_ and
_term_ into _multiplicative-expr_). But essentially just two new production
rules, i.e. _equality-expr_ and _relational-expr_, were added.

:links: Session 8, Page 4 -> doc:session08/page04#toc3


---- LATEX ---------------------------------------------------------------------
\begin{array}{rcl}
\text{input-sequence}
    & = &
    \{\;
    $> \;
    \text{assignment-expr}\;
    \texttt{;}\;
    |\;
    $< \;
    \text{assignment-expr}\;
    \texttt{;}\;
    |\;
    \text{expr-statement}\;
    \}\;
    \\
\text{expr-statement}
    & = &
    \text{assignment-expr}\;
    \texttt{;}\;
    \\
\text{assignment-expr}
    & = &
    \text{equality-expr}\;
    [\;
    \texttt{=}\;
    \text{assignment-expr}\;
    ]\;
    \\
\text{equality-expr}
    & = &
    \text{relational-expr}\;
    \{\;
      (\;
      \texttt{"=="}\; |\; \texttt{"!="}\;
      )\;
      \text{relational-expr}
    \}
    \\
\text{relational-expr}
    & = &
    \text{additive-expr}\;
    \{\;
      (\;
      \texttt{">"}\; |\; \texttt{"<"}\; |\; \texttt{">="}\; |\; \texttt{"<="}\;
      )\;
      \text{additive-expr}
    \}
    \\
\text{additive-expr}
    & = &
    \text{multiplicative-expr}\;
    \{\;
      (\;
      \texttt{"+"}\; |\; \texttt{"-"}\;
      )\;
      \text{multiplicative-expr}
    \}
    \\
\text{multiplicative-expr}
    & = &
    \text{unary-expr}\;
    \{\;
      (\;
      \texttt{"*"}\; |\; \texttt{"/"}\; |\; \texttt{"%"}
      )\;
      \text{unary-expr}
    \}
    \\
\text{unary-expr}
    & = &
    \text{primary-expr}\;
    |\;
    (\; \texttt{"+"}\; |\; \texttt{"-"}\;)\;
    \text{unary-expr}
    \\
\text{primary-expr}
    & = &
    \text{identifier}\;
    \\
    & | &
    \text{dec-literal}\;
    \\
    & | &
    \text{hex-literal}\;
    \\
    & | &
    \text{oct-literal}\;
    \\
    & | &
    \texttt{"("}\;
    \text{assignment-expr}\;
    \texttt{")"}\;
    \\
\end{array}
--------------------------------------------------------------------------------

Exercise
========

In _enum ExprKind_ add constants for the new binary operators:

---- CODE (type=c) -------------------------------------------------------------
enum ExprKind
{
    EK_BINARY,
    // binary expression
    EK_ADD = EK_BINARY,
    EK_ASSIGN,
    EK_EQUAL,
    EK_NOT_EQUAL,
    EK_GREATER,
    EK_GREATER_EQUAL,
    EK_LESS,
    EK_LESS_EQUAL,
    EK_SUB,
    EK_MUL,
    EK_DIV,
    EK_MOD,
    EK_BINARY_END,

    // ...
};
--------------------------------------------------------------------------------

Update the parser for the new grammar:

- Rename parse functions to reflect the naming used in the grammar. E.g rename
  _parseExpr()_ into _parseAdditiveExpr()_, etc. This is annoying but when a
  project grows such modifications are part of the game.

- Add parse the functions _parseEqualityExpr()_ and _parseRelationalExpr()_ for
  the corresponding production rules.

What Should Work Now
~~~~~~~~~~~~~~~~~~~~
After this update make sure that you can build ``xtest_abc``:

---- SHELL (path=session24/git1/abc, hide) -------------------------------------
make clean
--------------------------------------------------------------------------------

---- SHELL (path=session24/git1/abc,fold) --------------------------------------
make
--------------------------------------------------------------------------------

Test the compiler with expressions like in this example (of course you can
extend this):

---- CODE (file=session24/git1/abc/test.abc) -----------------------------------
x == y;
x != y;
x <= y;
x >= y;
x < y;
x > y;
--------------------------------------------------------------------------------

If you also want to update const folding use

---- CODE (file=session24/git1/abc/test_cf.abc) --------------------------------
x == y;
x != y;
x <= y;
x >= y;
x < y;
x > y;
3 == 4;
3 != 4;
3 <= 4;
3 >= 4;
3 < 4;
3 > 4;
--------------------------------------------------------------------------------

Expected Error
~~~~~~~~~~~~~~
You will get an assertion failure from the code generator (i.e. in
``loadExpr()``) but you should not get a syntax error:

---- SHELL (path=session24/git1/abc) -------------------------------------------
./xtest_abc < test.abc
--------------------------------------------------------------------------------

So in the next step you should

- adapt the implementation of _loadExpr()_.
- handle in ``printExprNode()`` the new expression kinds.
- handle in ``constFoldBinary()`` the new expression kinds (optional).