XTRAN Example — Match & Replace C, C++, Java, or C# Expressions

In the rules below:

• this     indicates C, C++, Java, or C# pattern elements
• <this> indicates meta pattern elements

Note that XTRAN was told, using a rules language recursive iterator statement, to automatically apply the rules below recursively to every expression in the code being re-engineered.

---

Process Flowchart

Here is a flowchart for this process, in which the elements are color coded:

• BLUE for XTRAN versions (runnable programs)
• ORANGE for XTRAN rules (text files)
• RED for code

---

XTRAN rules:

The following rules effectively convert infix expression notation to prefix notation.

Original expression	Replacement expression
<expr1> + <expr2>	add(<expr1>, <expr2>)
<expr1> - <expr2>	sub(<expr1>, <expr2>)
<expr1> * <expr2>	mul(<expr1>, <expr2>)
<expr1> / <expr2>	div(<expr1>, <expr2>)
<expr1> = <expr2>	copy(&<expr1>, <expr2>)

Original code:

     a = b + (c - d) * (e - f) / g;

Re-engineered code:

     copy(&a, add(b, div(mul(sub(c, d), sub(e, f)), g)));

---

XTRAN rule:

In the following rule, the match of a "wildcard" pattern element has a qualifying condition; if that condition evaluates to false, the match fails at that element.

Original expression	Replacement expression	Qualifying condition
copy(<expr1>, <expr2>)	*<expr1> = <expr2>	<expr2> is not an operator expression

Original code:

     copy(p_var1, *p_var2);
     copy(p_var3, var4);
     copy(p_var5, var6 + var7);
     copy(p_var8 + 3, var9);

Re-engineered code:

     copy(p_var1, *p_var2);
     *p_var3 = var4;
     copy(p_var5, var6 + var7);
     *(p_var8 + 3) = var9;