<div dir="ltr"><div>So I've finally had a chance to revisit my tictactoe game. </div><div><blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px"><div><font color="#999999"><br class="">import Control.Lens</font></div><div><font color="#999999"><br></font></div><div><font color="#999999">data Piece = X | O | E deriving Show</font></div><div><font color="#999999">type Row = [Piece]</font></div><div><font color="#999999">type Board = [Row]</font></div><div><b><i><font color="#000000">data Position = Int Int deriving Show</font></i></b></div><div><br></div><div><font color="#999999">-- put an X or O in a position</font></div><div><b><i><font color="#000000">move :: Board -> Piece -> Position -> Board</font></i></b></div><div><font color="#999999">move board piece position = board</font></div><div><br></div><div><font color="#999999">main :: IO ()</font></div><div><font color="#999999">main = putStrLn "Hello World"</font></div><div><font color="#999999"><br></font></div><div><font color="#999999">-- using Lenses</font></div><div><font color="#999999">-- <a href="https://github.com/ekmett/lens/wiki/Examples">https://github.com/ekmett/lens/wiki/Examples</a></font></div><div><font color="#999999">-- <a href="http://lens.github.io/tutorial.html">http://lens.github.io/tutorial.html</a></font></div><div><font color="#999999">-- <a href="http://blog.jakubarnold.cz/2014/07/14/lens-tutorial-introduction-part-1.html">http://blog.jakubarnold.cz/2014/07/14/lens-tutorial-introduction-part-1.html</a></font></div><div><font color="#999999"><br></font></div><div><font color="#999999">--let r1 = (E,E,E)</font></div><div><font color="#999999">--let r2 = (E,E,E)</font></div><div><font color="#999999">--let r3 = (E,E,E)</font></div><div><font color="#999999">--let board = (r1,r2,r3)</font></div></blockquote><div><br></div></div><div>Now, if I want to make a move, I'll want to set a <b><i>piece</i></b> on a <b><i>position</i></b>, on a <b><i>board</i></b>. Let's assume the board has the following shape. </div><div><br></div><blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px"><div><div><span style="color:rgb(0,0,0)">λ></span><span style="color:rgb(0,0,0)"> </span><font color="#000000">let r1 = (E,E,E)</font></div></div><div><div><span style="color:rgb(0,0,0)">λ></span><span style="color:rgb(0,0,0)"> </span><font color="#000000">let r2 = (E,E,E)</font></div></div><div><div><span style="color:rgb(0,0,0)">λ></span><span style="color:rgb(0,0,0)"> </span><font color="#000000">let r3 = (E,E,E)</font></div></div><div><div><font color="#000000">λ> let board = (r1,r2,r3)</font></div></div><div><font color="#999999">((E,E,E),(E,E,E),(E,E,E))</font></div></blockquote><div><font color="#999999"><br></font></div><div>To return an updated board, I dug around and <b><i>i)</i></b> couldn't find a core Haskell equivalent to Clojure's <a href="http://clojuredocs.org/clojure.core/update-in">update-in</a>. <b><i>ii)</i></b> Zippers only deal with trees of left / right nodes. <b><i>iii)</i></b> So that left me with <a href="https://github.com/ekmett/lens/wiki/Examples">Control.Lens</a>. Now I can easily inspect and update the board like so. </div><div><br></div><blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px"><div><div><font color="#999999">λ> board^</font><font color="#000000"><b><i>._</i></b><b><i>2._1</i></b></font></div></div><div><div><font color="#999999">E</font></div></div><div><div><font color="#999999">λ> set (</font><b><i><font color="#000000">_2._1</font></i></b><font color="#999999">) 42 board</font></div></div><div><div><font color="#999999">((E,E,E),(42,E,E),(E,E,E))</font></div></div></blockquote><div><br></div><div>I can then parameterize _2 or _1 like so. </div><div><br></div><blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px"><span style="color:rgb(153,153,153)">λ> </span><span style="color:rgb(153,153,153)">let a = _2<br></span><span style="color:rgb(153,153,153)">λ> </span><span style="color:rgb(153,153,153)">board ^. a</span><div><font color="#999999">(E,E,E)</font></div></blockquote><div><div class="gmail_extra"><br></div><div class="gmail_extra">But I can't figure out how to include that parameter's type into a <b><i>Position</i></b> type definition. I've tried these unsuccessfully. </div><div class="gmail_extra"><br></div></div><blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px"><div><div class="gmail_extra"><i><font color="#990000">data Position = Int Int deriving Show -- original type definition</font></i></div></div><div><div class="gmail_extra"><i><font color="#990000">data Position = Simple Lens (Int a) (Int a) deriving Show -- failing try 1</font></i></div></div><div><div class="gmail_extra"><br></div></div><div><div class="gmail_extra">move :: Board -> Piece -> Position -> Board</div></div><div class="gmail_extra">move board piece position = set (position) piece board -- want to use this instead of "<font color="#999999">set (</font><b><i><font color="#000000">_2._1</font></i></b><font color="#999999">) 42 board"</font></div></blockquote><div><div class="gmail_extra"><br></div><div class="gmail_extra"><br></div><div class="gmail_extra">Any ideas? </div><div class="gmail_extra"><br></div><div class="gmail_extra"><br></div><div class="gmail_extra">:) </div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature"><div dir="ltr"><div style="font-family:arial;font-size:small">Tim Washington </div><div style="font-family:arial;font-size:small"><a href="http://interruptsoftware.com" style="color:rgb(17,85,204)" target="_blank">Interruptsoftware.com</a> </div></div></div></div>
<div class="gmail_extra"><br></div><br><div class="gmail_quote">On Thu, Mar 12, 2015 at 5:18 PM, Timothy Washington <span dir="ltr"><<a href="mailto:twashing@gmail.com" target="_blank">twashing@gmail.com</a>></span> wrote:<font color="#999999"><br></font><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"><div><font color="#999999">Veeery nice. Thanks for your insights. </font></div><div><font color="#999999"><br></font></div><div><font color="#999999">The Typeclass stuff making a lot more sense now. And hence ghc-mod's (Interactive-Haskell's) behaviour makes more sense to me. It's working like a charm. </font></div><div class="gmail_extra"><font color="#999999"><br></font></div><div class="gmail_extra"><font color="#999999">I'll play around with nested list manipulation this evening.</font></div><div class="gmail_extra"><font color="#999999"><br></font></div><div class="gmail_extra"><font color="#999999"><br></font></div><div class="gmail_extra"><font color="#999999">Cheers </font></div><div class="gmail_extra"><font color="#999999"><br></font></div><div class="gmail_extra"><div><div><div dir="ltr"><div style="font-family:arial;font-size:small"><font color="#999999">Tim Washington </font></div><div style="font-family:arial;font-size:small"><font color="#999999"><a href="http://interruptsoftware.com" target="_blank">Interruptsoftware.com</a> </font></div></div></div></div><div><div class="h5">
<div class="gmail_extra"><font color="#999999"><br></font></div><font color="#999999"><br></font><div class="gmail_quote"><font color="#999999">On Thu, Mar 12, 2015 at 8:03 PM, Mike Meyer <span dir="ltr"><<a href="mailto:mwm@mired.org" target="_blank">mwm@mired.org</a>></span> wrote:<br></font><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><span><font color="#999999">On Thu, Mar 12, 2015 at 6:02 PM, Timothy Washington <span dir="ltr"><<a href="mailto:twashing@gmail.com" target="_blank">twashing@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr">To get started, I'm trying to implement a simple <i>tictactoe</i> game. And I would like to be able to represent a Piece on the board, as either the string "X" or "O". This is what I have so far. <div><br></div><blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px"><div><div>module Main where</div></div><div><div><br></div></div><div><div>data Piece = X | O</div></div><div><div>type Row = [Piece]</div></div><div><div>type Board = [Row]</div></div><div><div><br></div></div><div><div>-- put an X or O in a position</div></div><div><div>move :: Board -> Piece -> Board</div></div><div><div>move board piece = board</div></div><div><div> </div></div><div><div>-- check win vertically</div></div><div><div>-- check win horizontally</div></div><div><div>-- check win diagonally</div></div><div><div><br></div></div><div><div>main :: IO ()</div></div><div><div>main = putStrLn "Hello World"</div></div></blockquote><div><br></div><div><br></div><div><b><i>A)</i></b> Now, I'd like to be able to <b><i>load code interactively</i></b>, preferably within emacs. However I don't have access to my types with <b><i>ghci</i></b> or <b><i>ghc-mod (Interactive-Haskell)</i></b>. In either case, this call fails with the below error.</div><blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px"><div><div><br></div></div><div><div>let p = Piece X</div></div><div><div><interactive>:20:9-13: Not in scope: data constructor `Piece'</div></div></blockquote></div></blockquote><div><br></div></font></span><div><font color="#999999">Piece is the data TYPE. It has two constructors, X, and O. If you load your module into ghci, you can do ":t X" to get the type of X, which is Piece. You want to do "let p = X" here.</font></div><div><font color="#999999"><br></font></div><div><font color="#999999">Check your mode docs while editing the haskell file. There should be a command to load the current buffer into a ghci running in an interactive emacs buffer.</font></div><span><font color="#999999"><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr"><div><div><b><i>B)</i></b> And how do I make a <b><i>custom datatype</i></b> that's one of two strings (enumeration of either "X" or "O"). Cabal builds and runs the abouve code, so I know it can compile. But I'm confused as to where X or O is defined, and how I would supply it as an input. </div></div></div></blockquote><div><br></div><div><br></div></font></span><div><font color="#999999">As noted, you can derive "Show" so that Piece types print as "X" and "O". Similarly, you can derive "Read":</font></div><div><font color="#999999"><br></font></div><div><font color="#999999">data Piece = X | O deriving (Show, Read)</font></div><div><font color="#999999"><br></font></div><div><font color="#999999">so that you can then read "X" and get back an X when the context calls for a Piece value:</font></div><div>
<p><font color="#999999">*Main> read "X" :: Piece</font></p>
<p><font color="#999999">X</font></p></div><div><font color="#999999"><br></font></div><div><font color="#999999">However, this isn't used a lot, as it tends to be slow and not very flexible for more complex types. For instance, it will let you read in lists of Pieces and lists of lists, but you'l lhave to use the list syntax, not something that looks like an actual board when printed.</font></div><div><br></div></div></div></div></blockquote></div></div></div></div></div></blockquote></div></div></div></div>