Scrap your boilerplate

Scrap your boilerplate (SYB) is another early approach to datatype-generic programming, that is, it provides a way to define generic functions over a "universal" type representation.

SYB differs from the other two approaches we have explored in that the type representation is obfuscated from the user.

Earlier versions of the SYB approach had a strong focus on generic traversals over complex nested data structures, for example:

data Book     = Book     Title [Chapter]
data Chapter   = Chapter Title [Section]
data Section   = Section Title [Para]
type Title     = String; type Para = String

haskellDP = Book "Haskell Design Patterns" chapters

chapters  = [Chapter "The building blocks" sections1, 
             Chapter "IO Patterns" sections2] 
 
sections1 = [Section "1.1" ["Lorem lorem"],  
             Section "1.2" ["Lorem lorem", "Lorem lorem"]] 
 
sections2 = [Section "2.1" ["Ipsum Ipsum"], 
             Section "2.2" ["Ipsum Ipsum", "Ipsum Ipsum"]] 

Suppose we have...