Loops/Increment loop index within loop body: Difference between revisions
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(Undo revision 278942 by Nigel Galloway (talk)) |
(Realize in F#) |
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</pre> |
</pre> |
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=={{header|F_Sharp|F#}}== |
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This task uses [http://www.rosettacode.org/wiki/Extensible_prime_generator#The_function Extensible Prime Generator (F#)] |
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<lang fsharp> |
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// Well I don't do loops. Nigel Galloway: March 17th., 2019. Let me try to explain where the loopy variables are, for the imperatively constrained. |
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// cUL allows me to claim the rather trivial extra credit (commas in the numbers) |
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let cUL=let g=System.Globalization.CultureInfo("en-GB") in (fun (n:uint64)->n.ToString("N0",g)) |
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// fN is primality by trial division |
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let fN g=pCache|>Seq.map uint64|>Seq.takeWhile(fun n->n*n<g)|>Seq.forall(fun n->g%n>0UL) |
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// unfold is sort of a loop incremented by 1 in this case |
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let fG n=Seq.unfold(fun n->Some(n,(n+1UL))) n|>Seq.find(fN) |
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// unfold is sort of a loop with fG as an internal loop incremented by twice the exit value of the internal loop in this case. |
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Seq.unfold(fun n->let n=fG n in Some(n,n+n)) 42UL|>Seq.take 42|>Seq.iteri(fun n g->printfn "%2d -> %s" (n+1) (cUL g)) |
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</lang> |
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{{out}} |
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<pre> |
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1 -> 43 |
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2 -> 89 |
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3 -> 179 |
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4 -> 359 |
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5 -> 719 |
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6 -> 1,439 |
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7 -> 2,879 |
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8 -> 5,779 |
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9 -> 11,579 |
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10 -> 23,159 |
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11 -> 46,327 |
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12 -> 92,657 |
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13 -> 185,323 |
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14 -> 370,661 |
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15 -> 741,337 |
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16 -> 1,482,707 |
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17 -> 2,965,421 |
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18 -> 5,930,887 |
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19 -> 11,861,791 |
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20 -> 23,723,597 |
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21 -> 47,447,201 |
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22 -> 94,894,427 |
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23 -> 189,788,857 |
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24 -> 379,577,741 |
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25 -> 759,155,483 |
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26 -> 1,518,310,967 |
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27 -> 3,036,621,941 |
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28 -> 6,073,243,889 |
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29 -> 12,146,487,779 |
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30 -> 24,292,975,649 |
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31 -> 48,585,951,311 |
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32 -> 97,171,902,629 |
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33 -> 194,343,805,267 |
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34 -> 388,687,610,539 |
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35 -> 777,375,221,081 |
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36 -> 1,554,750,442,183 |
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37 -> 3,109,500,884,389 |
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38 -> 6,219,001,768,781 |
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39 -> 12,438,003,537,571 |
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40 -> 24,876,007,075,181 |
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41 -> 49,752,014,150,467 |
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42 -> 99,504,028,301,131 |
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</pre> |
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=={{header|Factor}}== |
=={{header|Factor}}== |
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Explicit loop indices are non-idiomatic, but Factor is certainly capable of using them. Factor has a for loop near-equivalent, <code><range> [ ] each</code>, but since it doesn't mesh well with mutation, a while loop is used. |
Explicit loop indices are non-idiomatic, but Factor is certainly capable of using them. Factor has a for loop near-equivalent, <code><range> [ ] each</code>, but since it doesn't mesh well with mutation, a while loop is used. |