SI413: Debug's

One of the extensions is to implement "debug". I ended up stripping this out of one of your earlier labs, so I'll catch you up on it now.

Debugging statements are little snippets of text that print to the screen when a certain part of your code is reached. Since SPL doesn't have any support for strings, we have to add a language feature to support this. Our approach will be that anything enclosed in double-quotes is a debugging statement. This will require a new AST Stmt node class called Debug, which you will have to create.

Some specifics on the debug statements

The debug statements can go in between other statements, but not in the middle. So
```
write 5; "hello!" write 6;
```
would be OK, but not
```
write "the interruptor!" 5;
```
Debug statements do not need to be followed by a semicolon.
Because debug statements are going into your AST, they should be executed every time that part of the program is executed. So for example, running
```
if false { "toodaloo" }
```
should not result in any output.

$ echo "new i := 0; while i < 3 { "here" write i; i := i + 1; }" | ./splc > tmp.ll
$ lli tmp.ll
here
0
here
1
here
2

Below are simple instructions for how to get your compiler set up for debug's ... of course how to actually do exec for debug statements is up to you!

In spl.lpp

You should add this function defintion:

// Strips leading and trailing quote marks
// from the given C string
char* quotestrip(char* str) {
  char* toret = str;
  while (toret[0] == '"') ++toret;
  for (int i=0; toret[i] != '\0'; ++i) {
    if (toret[i] == '"') toret[i] = '\0';
  }
  return toret;
}

... and add this to your token rules:

["][^"]*["] {yylval.stmt = new Debug(quotestrip(yytext)); return DEBUG;}

In spl.ypp

You'll have to add this to your toeken definitions:

%token<stmt< DEBUG

and this to your grammar rules for statements:

|     DEBUG                  {$$ = $1;}

In ast.hpp

You'll have to add this class:

/* A debugging statement embedded in the code. */
class Debug :public Stmt {
  private:
    string msg;

  public:
    Debug(const string& themsg) {
      msg = themsg;
    }
};