FPSE

Idiomatic Functional Programming

Examples of Idiomatic FP

Here are example codebases we will spend time inspecting and critiqueing.

Minesweeper

• Minesweeper at Exercism.io
• Its not the full game, just calculating the number of mines adjacent to each non-mine square
• Example input/input:

    [ "  *  ";
      "  *  ";
      "*****";
      "  *  ";
      "  *  "; ]
  
    [ " 2*2 ";
      "25*52";
      "*****";
      "25*52";
      " 2*2 "; ]
  

  See test.ml for more examples

  • Before getting into the code let’s consider algorithms, there are two distinct approaches
    1. For each non-mine square look around it and add up the mines
    2. Or, for each mine square increment the count on all non-mine squares around it (start at 0)
  • The latter is fundamentally more difficult to do functionally
    • The grid will need to change (mutate) a great many times as counts bump up one by one
  • The former can produce the complete answer for a given cell in one go, no incrementalism
  • We will review this functional solution
  • We made another variation on the functional version to be cleaner and more efficient
  • Will look at an imperative approach which has some poor abstractions and fails to use combinators.
  • All of these minesweeper versions are in this zip file

Other Examples

• ocaml-cuid is a utility to generate highly random string IDs for webpages etc.
  • Lots of nice piping here plus use of functors to build Unix and JavaScript variations
• dolog is a very simple logging utility
  • Shows some nice use of state, include, and a Make functor.
• We may also look at a past homework solution so you can compare it with what you did.