34 lines
784 B
Raku
34 lines
784 B
Raku
# based on http://www.mathpropress.com/stan/bibliography/spigot.pdf
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sub stream(&next, &safe, &prod, &cons, $z is copy, @x) {
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gather loop {
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$z = safe($z, my $y = next($z)) ??
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prod($z, take $y) !!
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cons($z, @x[$++])
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}
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}
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sub extr([$q, $r, $s, $t], $x) {
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($q * $x + $r) div ($s * $x + $t)
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}
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sub comp([$q,$r,$s,$t], [$u,$v,$w,$x]) {
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[$q * $u + $r * $w,
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$q * $v + $r * $x,
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$s * $u + $t * $w,
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$s * $v + $t * $x]
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}
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my $pi :=
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stream -> $z { extr($z, 3) },
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-> $z, $n { $n == extr($z, 4) },
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-> $z, $n { comp([10, -10*$n, 0, 1], $z) },
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&comp,
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<1 0 0 1>,
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(1..*).map: { [$_, 4 * $_ + 2, 0, 2 * $_ + 1] }
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for ^Inf -> $i {
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print $pi[$i];
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once print '.'
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}
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