Uniplate

This library (formerly known as 'Play') provides a framework for generic traversals, and is intended to be used in a similar manner to the original Scrap Your Boilerplate paper.

An example of how Uniplate can reduce boilerplate:

data Expr  =  Add  Expr  Expr  | Val  Int
           |  Sub  Expr  Expr  | Var  String
           |  Mul  Expr  Expr  | Neg  Expr
           |  Div  Expr  Expr

variables :: Expr -> [String]
variables (Var  x  ) = [x]
variables (Val  x  ) = []
variables (Neg  x  ) = variables x
variables (Add  x y) = variables x ++ variables y
variables (Sub  x y) = variables x ++ variables y
variables (Mul  x y) = variables x ++ variables y
variables (Div  x y) = variables x ++ variables y

The code for variables is not very nice, however, using Uniplate we can rewrite this as:

variables :: Expr -> [String]
variables x = [y | Var y <- universe x]

Downloads

• Released version
  • Boilerplate Removal with Uniplate (bibtex)(hide bibtex)
    @manual{mitchell:uniplate_manual
        ,title          = "Boilerplate Removal with {Uniplate}"
        ,author         = "Neil Mitchell"
        ,url            = "\verb'http://www.cs.york.ac.uk/fp/darcs/uniplate/uniplate.htm'"
    }
    
  • darcs get --partial http://www.cs.york.ac.uk/fp/darcs/uniplate
• Related blog posts
• Uniform Boilerplate and List Processing - from Haskell Workshop 2007 (abstract)(hide abstract)
  Generic traversals over recursive data structures are often referred to as boilerplate code. The definitions of functions involving such traversals may repeat very similar patterns, but with variations for different data types and different functionality. Libraries of operations abstracting away boilerplate code typically rely on elaborate types to make operations generic. The motivating observation for this paper is that most traversals have value-specific behaviour for just one type. We present the design of a new library exploiting this assumption. Our library allows concise expression of traversals with competitive performance.
  (bibtex)(hide bibtex)
  @inproceedings{mitchell:uniplate_2007_9_30
      ,title          = "Uniform Boilerplate and List Processing"
      ,author         = "Neil Mitchell and Colin Runciman"
      ,year           = "2007"
      ,month          = "September"
      ,day            = "30"
      ,booktitle      = "Haskell '07: Proceedings of the ACM SIGPLAN workshop on Haskell workshop"
      ,pages          = "49--60
      ,location       = "Freiburg, Germany"
      ,doi            = "http://doi.acm.org/10.1145/1291201.1291208"
      ,publisher      = "ACM"
      ,isbn           = "978-1-59593-674-5"
      ,url            = "\verb'http://www-users.cs.york.ac.uk/~ndm/downloads/paper-uniform_boilerplate_and_list_processing-30_sep_2007.pdf'"
  }
  
  • Uniform Boilerplate and List Processing - from Haskell Workshop 2007
  • Uniform Boilerplate and List Processing
• Playing with Haskell Data - from PLASMA (bibtex)(hide bibtex)
  @misc{mitchell:uniplate_2007_1_18
      ,title          = "Playing with {Haskell} Data"
      ,author         = "Neil Mitchell"
      ,year           = "2007"
      ,month          = "January"
      ,day            = "18"
      ,note           = "Presentation from PLASMA"
      ,url            = "\verb'http://www-users.cs.york.ac.uk/~ndm/downloads/slides-playing_with_haskell_data-18_jan_2007.pdf'"
  }
  

Tags: haskell library phd popular released