Thinking Forth p12

Successive Refinement

Successive Refinement
An approach that relies heavily on subroutines is called “Successive Refinement.”

 The idea is that you begin by writing a skeletal version of your program
using natural names for procedures for data structures.

Then you write versionsof each of the named procedures.

You continue this process to greater levels of detail until 
the procedures can only be written in the computer language itself.

At each step the programmer must make decisions about the algorithms
being used and about the data structures they’re being used on. Decisions
about the algorithms and associated data structures should be made in parallel.
If an approach doesn’t work out the programmer is encouraged to back
track as far as necessary and start again.

Notice this about successive refinement: You can’t actually run any part
of the program until its lowest-level components are written. Typically this
means you can’t test the program until after you’ve completely designed it.
Also notice: Successive refinement forces you to work out all details of
control structure on each level before proceeding to the next lower level.