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copied!<p>If you want it to be very pretty, you could steal about 25 lines of code from <a href="http://lorgonblog.spaces.live.com/blog/cns!701679AD17B6D310!248.entry" rel="noreferrer">this blog entry</a> to draw it with WPF.</p> <p>But I'll code up an ascii solution shortly too, probably.</p> <p>EDIT</p> <p>Ok, wow, that was hard.</p> <p>I'm not certain it's entirely correct, and I can't help but think there's probably a better abstraction. But anyway... enjoy! </p> <p>(See the end of the code for a large example that is rather pretty.)</p> <pre><code>type 'a tree = | Node of 'a tree * 'a * 'a tree | Nil (* For any given tree ddd / \ lll rrr we think about it as these three sections, left|middle|right (L|M|R): d | d | d / | | \ lll | | rrr M is always exactly one character. L will be as wide as either (d's width / 2) or L's width, whichever is more (and always at least one) R will be as wide as either ((d's width - 1) / 2) or R's width, whichever is more (and always at least one) (above two lines mean 'dddd' of even length is slightly off-center left) We want the '/' to appear directly above the rightmost character of the direct left child. We want the '\' to appear directly above the leftmost character of the direct right child. If the width of 'ddd' is not long enough to reach within 1 character of the slashes, we widen 'ddd' with underscore characters on that side until it is wide enough. *) // PrettyAndWidthInfo : 'a tree -> string[] * int * int * int // strings are all the same width (space padded if needed) // first int is that total width // second int is the column the root node starts in // third int is the column the root node ends in // (assumes d.ToString() never returns empty string) let rec PrettyAndWidthInfo t = match t with | Nil -> [], 0, 0, 0 | Node(Nil,d,Nil) -> let s = d.ToString() [s], s.Length, 0, s.Length-1 | Node(l,d,r) -> // compute info for string of this node's data let s = d.ToString() let sw = s.Length let swl = sw/2 let swr = (sw-1)/2 assert(swl+1+swr = sw) // recurse let lp,lw,_,lc = PrettyAndWidthInfo l let rp,rw,rc,_ = PrettyAndWidthInfo r // account for absent subtrees let lw,lb = if lw=0 then 1," " else lw,"/" let rw,rb = if rw=0 then 1," " else rw,"\\" // compute full width of this tree let totalLeftWidth = (max (max lw swl) 1) let totalRightWidth = (max (max rw swr) 1) let w = totalLeftWidth + 1 + totalRightWidth (* A suggestive example: dddd | d | dddd__ / | | \ lll | | rr | | ... | | rrrrrrrrrrr ---- ---- swl, swr (left/right string width (of this node) before any padding) --- ----------- lw, rw (left/right width (of subtree) before any padding) ---- totalLeftWidth ----------- totalRightWidth ---- - ----------- w (total width) *) // get right column info that accounts for left side let rc2 = totalLeftWidth + 1 + rc // make left and right tree same height let lp = if lp.Length < rp.Length then lp @ List.init (rp.Length-lp.Length) (fun _ -> "") else lp let rp = if rp.Length < lp.Length then rp @ List.init (lp.Length-rp.Length) (fun _ -> "") else rp // widen left and right trees if necessary (in case parent node is wider, and also to fix the 'added height') let lp = lp |> List.map (fun s -> if s.Length < totalLeftWidth then (nSpaces (totalLeftWidth - s.Length)) + s else s) let rp = rp |> List.map (fun s -> if s.Length < totalRightWidth then s + (nSpaces (totalRightWidth - s.Length)) else s) // first part of line1 let line1 = if swl < lw - lc - 1 then (nSpaces (lc + 1)) + (nBars (lw - lc - swl)) + s else (nSpaces (totalLeftWidth - swl)) + s // line1 right bars let line1 = if rc2 > line1.Length then line1 + (nBars (rc2 - line1.Length)) else line1 // line1 right padding let line1 = line1 + (nSpaces (w - line1.Length)) // first part of line2 let line2 = (nSpaces (totalLeftWidth - lw + lc)) + lb // pad rest of left half let line2 = line2 + (nSpaces (totalLeftWidth - line2.Length)) // add right content let line2 = line2 + " " + (nSpaces rc) + rb // add right padding let line2 = line2 + (nSpaces (w - line2.Length)) let resultLines = line1 :: line2 :: ((lp,rp) ||> List.map2 (fun l r -> l + " " + r)) for x in resultLines do assert(x.Length = w) resultLines, w, lw-swl, totalLeftWidth+1+swr and nSpaces n = String.replicate n " " and nBars n = String.replicate n "_" let PrettyPrint t = let sl,_,_,_ = PrettyAndWidthInfo t for s in sl do printfn "%s" s let y = Node(Node (Node (Nil,35,Node (Node(Nil,1,Nil),88888888,Nil)),48,Node (Nil,777777777,Node (Nil,53,Nil))), 80,Node (Node (Nil,82,Node (Nil,83,Nil)),1111111111,Node (Nil,98,Nil))) let z = Node(y,55555,y) let x = Node(z,4444,y) PrettyPrint x (* ___________________________4444_________________ / \ ________55555________________ ________80 / \ / \ ________80 ________80 _______48 1111111111 / \ / \ / \ / \ _______48 1111111111 _______48 1111111111 35 777777777 82 98 / \ / \ / \ / \ \ \ \ 35 777777777 82 98 35 777777777 82 98 88888888 53 83 \ \ \ \ \ \ / 88888888 53 83 88888888 53 83 1 / / 1 1 *) </code></pre>

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