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<a href='https://github.com/akkartik/mu/blob/master/nqueens.mu'>https://github.com/akkartik/mu/blob/master/nqueens.mu</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="Comment"># <a href="http://rosettacode.org/wiki/N-queens_problem">http://rosettacode.org/wiki/N-queens_problem</a></span>
<span id="L2" class="LineNr"> 2 </span><span class="Comment"># port of the Arc solution at <a href="http://arclanguage.org/item?id=19743">http://arclanguage.org/item?id=19743</a></span>
<span id="L3" class="LineNr"> 3 </span><span class="Comment"># run with tracing turned on:</span>
<span id="L4" class="LineNr"> 4 </span><span class="Comment"># ./mu --trace nqueens.mu</span>
<span id="L5" class="LineNr"> 5 </span>
<span id="L6" class="LineNr"> 6 </span><span class="muData">container</span> <a href='nqueens.mu.html#L6'>square</a> [
<span id="L7" class="LineNr"> 7 </span> rank:num
<span id="L8" class="LineNr"> 8 </span> file:num
<span id="L9" class="LineNr"> 9 </span>]
<span id="L10" class="LineNr"> 10 </span>
<span id="L11" class="LineNr"> 11 </span><span class="muRecipe">def</span> <a href='nqueens.mu.html#L11'>nqueens</a> n:num, queens:&:<a href='064list.mu.html#L6'>list</a>:<a href='nqueens.mu.html#L6'>square</a><span class="muRecipe"> -> </span>result:num, queens:&:<a href='064list.mu.html#L6'>list</a>:<a href='nqueens.mu.html#L6'>square</a> [
<span id="L12" class="LineNr"> 12 </span> <span class="Constant">local-scope</span>
<span id="L13" class="LineNr"> 13 </span> <span class="Constant">load-inputs</span>
<span id="L14" class="LineNr"> 14 </span> <span class="Comment"># if 'queens' is already long enough, print it and return</span>
<span id="L15" class="LineNr"> 15 </span> added-so-far:num <span class="Special"><-</span> length queens
<span id="L16" class="LineNr"> 16 </span> <span class="Delimiter">{</span>
<span id="L17" class="LineNr"> 17 </span> done?:bool <span class="Special"><-</span> greater-or-equal added-so-far, n
<span id="L18" class="LineNr"> 18 </span> <span class="muControl">break-unless</span> done?
<span id="L19" class="LineNr"> 19 </span> stash queens
<span id="L20" class="LineNr"> 20 </span> <span class="muControl"> return</span><span class="Constant"> 1</span>
<span id="L21" class="LineNr"> 21 </span> <span class="Delimiter">}</span>
<span id="L22" class="LineNr"> 22 </span> <span class="Comment"># still work to do</span>
<span id="L23" class="LineNr"> 23 </span> next-rank:num <span class="Special"><-</span> copy<span class="Constant"> 0</span>
<span id="L24" class="LineNr"> 24 </span> <span class="Delimiter">{</span>
<span id="L25" class="LineNr"> 25 </span> <span class="muControl">break-unless</span> queens
<span id="L26" class="LineNr"> 26 </span> first:<a href='nqueens.mu.html#L6'>square</a> <span class="Special"><-</span> first queens
<span id="L27" class="LineNr"> 27 </span> existing-rank:num <span class="Special"><-</span> get first, <span class="Constant">rank:offset</span>
<span id="L28" class="LineNr"> 28 </span> next-rank <span class="Special"><-</span> add existing-rank,<span class="Constant"> 1</span>
<span id="L29" class="LineNr"> 29 </span> <span class="Delimiter">}</span>
<span id="L30" class="LineNr"> 30 </span> result <span class="Special"><-</span> copy<span class="Constant"> 0</span>
<span id="L31" class="LineNr"> 31 </span> next-file:num <span class="Special"><-</span> copy<span class="Constant"> 0</span>
<span id="L32" class="LineNr"> 32 </span> <span class="Delimiter">{</span>
<span id="L33" class="LineNr"> 33 </span> done?:bool <span class="Special"><-</span> greater-or-equal next-file, n
<span id="L34" class="LineNr"> 34 </span> <span class="muControl">break-if</span> done?
<span id="L35" class="LineNr"> 35 </span> curr:<a href='nqueens.mu.html#L6'>square</a> <span class="Special"><-</span> merge next-rank, next-file
<span id="L36" class="LineNr"> 36 </span> <span class="Delimiter">{</span>
<span id="L37" class="LineNr"> 37 </span> curr-conflicts?:bool <span class="Special"><-</span> <a href='nqueens.mu.html#L52'>conflict?</a> curr, queens
<span id="L38" class="LineNr"> 38 </span> <span class="muControl">break-if</span> curr-conflicts?
<span id="L39" class="LineNr"> 39 </span> new-queens:&:<a href='064list.mu.html#L6'>list</a>:<a href='nqueens.mu.html#L6'>square</a> <span class="Special"><-</span> push curr, queens
<span id="L40" class="LineNr"> 40 </span> sub-result:num <span class="Special"><-</span> <a href='nqueens.mu.html#L11'>nqueens</a> n, new-queens
<span id="L41" class="LineNr"> 41 </span> result <span class="Special"><-</span> add result, sub-result
<span id="L42" class="LineNr"> 42 </span> <span class="Delimiter">}</span>
<span id="L43" class="LineNr"> 43 </span> next-file <span class="Special"><-</span> add next-file,<span class="Constant"> 1</span>
<span id="L44" class="LineNr"> 44 </span> <span class="muControl"> loop</span>
<span id="L45" class="LineNr"> 45 </span> <span class="Delimiter">}</span>
<span id="L46" class="LineNr"> 46 </span>]
<span id="L47" class="LineNr"> 47 </span>
<span id="L48" class="LineNr"> 48 </span><span class="Comment"># check if putting a queen on 'curr' conflicts with any of the existing</span>
<span id="L49" class="LineNr"> 49 </span><span class="Comment"># queens</span>
<span id="L50" class="LineNr"> 50 </span><span class="Comment"># assumes that 'curr' is on a non-conflicting rank, and checks for conflict</span>
<span id="L51" class="LineNr"> 51 </span><span class="Comment"># only in files and diagonals</span>
<span id="L52" class="LineNr"> 52 </span><span class="muRecipe">def</span> <a href='nqueens.mu.html#L52'>conflict?</a> curr:<a href='nqueens.mu.html#L6'>square</a>, queens:&:<a href='064list.mu.html#L6'>list</a>:<a href='nqueens.mu.html#L6'>square</a><span class="muRecipe"> -> </span>result:bool [
<span id="L53" class="LineNr"> 53 </span> <span class="Constant">local-scope</span>
<span id="L54" class="LineNr"> 54 </span> <span class="Constant">load-inputs</span>
<span id="L55" class="LineNr"> 55 </span> result <span class="Special"><-</span> <a href='nqueens.mu.html#L60'>conflicting-file?</a> curr, queens
<span id="L56" class="LineNr"> 56 </span> <span class="muControl">return-if</span> result
<span id="L57" class="LineNr"> 57 </span> result <span class="Special"><-</span> <a href='nqueens.mu.html#L76'>conflicting-diagonal?</a> curr, queens
<span id="L58" class="LineNr"> 58 </span>]
<span id="L59" class="LineNr"> 59 </span>
<span id="L60" class="LineNr"> 60 </span><span class="muRecipe">def</span> <a href='nqueens.mu.html#L60'>conflicting-file?</a> curr:<a href='nqueens.mu.html#L6'>square</a>, queens:&:<a href='064list.mu.html#L6'>list</a>:<a href='nqueens.mu.html#L6'>square</a><span class="muRecipe"> -> </span>result:bool [
<span id="L61" class="LineNr"> 61 </span> <span class="Constant">local-scope</span>
<span id="L62" class="LineNr"> 62 </span> <span class="Constant">load-inputs</span>
<span id="L63" class="LineNr"> 63 </span> curr-file:num <span class="Special"><-</span> get curr, <span class="Constant">file:offset</span>
<span id="L64" class="LineNr"> 64 </span> <span class="Delimiter">{</span>
<span id="L65" class="LineNr"> 65 </span> <span class="muControl">break-unless</span> queens
<span id="L66" class="LineNr"> 66 </span> q:<a href='nqueens.mu.html#L6'>square</a> <span class="Special"><-</span> first queens
<span id="L67" class="LineNr"> 67 </span> qfile:num <span class="Special"><-</span> get q, <span class="Constant">file:offset</span>
<span id="L68" class="LineNr"> 68 </span> file-match?:bool <span class="Special"><-</span> equal curr-file, qfile
<span id="L69" class="LineNr"> 69 </span> <span class="muControl">return-if</span> file-match?,<span class="Constant"> true/conflict-found</span>
<span id="L70" class="LineNr"> 70 </span> queens <span class="Special"><-</span> <a href='064list.mu.html#L24'>rest</a> queens
<span id="L71" class="LineNr"> 71 </span> <span class="muControl"> loop</span>
<span id="L72" class="LineNr"> 72 </span> <span class="Delimiter">}</span>
<span id="L73" class="LineNr"> 73 </span> <span class="muControl"> return</span><span class="Constant"> false/no-conflict-found</span>
<span id="L74" class="LineNr"> 74 </span>]
<span id="L75" class="LineNr"> 75 </span>
<span id="L76" class="LineNr"> 76 </span><span class="muRecipe">def</span> <a href='nqueens.mu.html#L76'>conflicting-diagonal?</a> curr:<a href='nqueens.mu.html#L6'>square</a>, queens:&:<a href='064list.mu.html#L6'>list</a>:<a href='nqueens.mu.html#L6'>square</a><span class="muRecipe"> -> </span>result:bool [
<span id="L77" class="LineNr"> 77 </span> <span class="Constant">local-scope</span>
<span id="L78" class="LineNr"> 78 </span> <span class="Constant">load-inputs</span>
<span id="L79" class="LineNr"> 79 </span> curr-rank:num <span class="Special"><-</span> get curr, <span class="Constant">rank:offset</span>
<span id="L80" class="LineNr"> 80 </span> curr-file:num <span class="Special"><-</span> get curr, <span class="Constant">file:offset</span>
<span id="L81" class="LineNr"> 81 </span> <span class="Delimiter">{</span>
<span id="L82" class="LineNr"> 82 </span> <span class="muControl">break-unless</span> queens
<span id="L83" class="LineNr"> 83 </span> q:<a href='nqueens.mu.html#L6'>square</a> <span class="Special"><-</span> first queens
<span id="L84" class="LineNr"> 84 </span> qrank:num <span class="Special"><-</span> get q, <span class="Constant">rank:offset</span>
<span id="L85" class="LineNr"> 85 </span> qfile:num <span class="Special"><-</span> get q, <span class="Constant">file:offset</span>
<span id="L86" class="LineNr"> 86 </span> rank-delta:num <span class="Special"><-</span> subtract qrank, curr-rank
<span id="L87" class="LineNr"> 87 </span> file-delta:num <span class="Special"><-</span> subtract qfile, curr-file
<span id="L88" class="LineNr"> 88 </span> rank-delta <span class="Special"><-</span> <a href='070table.mu.html#L103'>abs</a> rank-delta
<span id="L89" class="LineNr"> 89 </span> file-delta <span class="Special"><-</span> <a href='070table.mu.html#L103'>abs</a> file-delta
<span id="L90" class="LineNr"> 90 </span> diagonal-match?:bool <span class="Special"><-</span> equal rank-delta, file-delta
<span id="L91" class="LineNr"> 91 </span> <span class="muControl">return-if</span> diagonal-match?,<span class="Constant"> true/conflict-found</span>
<span id="L92" class="LineNr"> 92 </span> queens <span class="Special"><-</span> <a href='064list.mu.html#L24'>rest</a> queens
<span id="L93" class="LineNr"> 93 </span> <span class="muControl"> loop</span>
<span id="L94" class="LineNr"> 94 </span> <span class="Delimiter">}</span>
<span id="L95" class="LineNr"> 95 </span> <span class="muControl"> return</span><span class="Constant"> false/no-conflict-found</span>
<span id="L96" class="LineNr"> 96 </span>]
<span id="L97" class="LineNr"> 97 </span>
<span id="L98" class="LineNr"> 98 </span><span class="muRecipe">def</span> <a href='nqueens.mu.html#L98'>main</a> [
<span id="L99" class="LineNr"> 99 </span> <a href='nqueens.mu.html#L11'>nqueens</a><span class="Constant"> 4</span>
<span id="L100" class="LineNr">100 </span> $dump-trace <span class="Constant">[app]</span>
<span id="L101" class="LineNr">101 </span>]
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