I don't know php, are you looking for println(varName)? Also there is a library for debugging Processing, it's for 2.0 only i think, i never tested it.

Hmm.. It's a function that prints out a variable's type and value so that you know whats exactly inside. It will list out the structure of the variable too if it's an array or object.

this will print the value, not the type or structure... 

println(someArray) will do the right thing in Processing.
println(anArrayList) too, idem for most Java collections.
println(customMadeObject) can work only if your class defines a toString method, which is a good practice anyway.
For example:

1. class Circle
2. {
3.   int x, y;
4.   color c;
5.   int diameter;
6. // Various stuff about this circle, including a display() or similar method
7. // Then:
8.   public String toString()
9.   {
10.     return "Circle[at (" + x + "," + y + "), color=" + hex(c) + ", diameter=" + diameter + "]";
11.   }
12. }

This toString() method is automatically called by stuff like println(), or when concatenating the object in a string, etc.
As you can see, it is a bit more work than an automated method, but it is also more flexible, as you can choose what fields to display (you can omit temp fields or non-important ones), the display order, the format, what to put around it, etc.