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<?php /* span :: (a -> Bool) -> [a] -> ([a],[a]) span _ xs@[] = (xs, xs) span p xs@(x:xs') | p x = let (ys,zs) = span p xs' in (x:ys,zs) | otherwise = ([],xs) */ function span($p, $xs) { if (empty($xs)) { return [[], []]; } $xs_ = $xs; $x = array_shift($xs_); if ($p($x)) { list($ys, $zs) = span($p, $xs_); return [array_merge([$x], $ys), $zs]; } return [[], $xs]; } /* groupBy :: (a -> a -> Bool) -> [a] -> [[a]] groupBy _ [] = [] groupBy eq (x:xs) = (x:ys) : groupBy eq zs where (ys,zs) = span (eq x) xs */ function array_group(callable $eq, array $xs) { if (empty($xs)) { return []; } $x = array_shift($xs); // curry of $eq $eqx = function ($y) use ($eq, $x) { return $eq($x, $y); }; list($ys, $zs) = span($eqx, $xs); return array_merge([array_merge([$x], $ys)], array_group($eq, $zs)); } function it($m,$p){echo ($p?'OK':'NO')." It $m\n"; if(!$p){$GLOBALS['f']=1;}}function done(){if(@$GLOBALS['f'])die(1);} it('spans elements which match', span(function ($x) { return $x < 3; }, [1, 2, 3]) === [[1, 2], [3]]); it('spans elements which match from the start', span(function ($x) { return $x == 3; }, [1, 6, 3, 3]) === [[], [1, 2, 3, 3]]); it('spans returns empty lists on empty list', span(function ($x) { return false; }, []) === [[], []]); it('groups elements recursively', array_group(function ($a, $b) { return $a === $b; }, [1, 1, 2, 1]) === [[1, 1], [2], [1]]);

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