Functional Programming Patterns.

Roundabout presents a set of patterns for writing recursive programs.

• Structural Recursion - use recursion to traverse inductively defined data structures (e.g. list ortree)


• Interface Procedure - use a helper method to adapt a function call if you need an extra argument


• Mutual Recursion - use multiple recursive functions to traverse inductively defined data structures where elements in the data structure are also inductively defined


• Accumulator Variable - use an additional parameter to carry calculations through recursion


• Syntax Procedure - extract methods that mean something rather than accessing raw members of data structures (e.g. for trees written as lists use (lhs foo) instead of (first foo)


• Local Procedure - use anonymous methods to hide details from the outside world


• Program Derivation - inline code if you want more performance

The relationship between patterns and refactoring has already been written about ("Refactoring to Patterns"). In this case the relationships are quite clear.

• Program Derivation => inline method.
  
• Interface Procedure => adapter pattern
  
• Local Procedure => encapsulation
  
• Syntax Procedure => extract method
  
• Structural Recursion/ Mutual Recursion => Visitor Pattern (might be a bit tenuous!)
  

Not all of the patterns are directly applicable to all languages. For example, Program Derivation is unwarranted for Lisp type languages because macros provide all those capabilities. I guess that's another one for the design patterns are a weakness of the language meme.