19 lines
254 B
Plaintext
19 lines
254 B
Plaintext
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###
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### combine2.1
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###
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## Chapter 7 section 1
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sub combine2 {
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my $op = shift;
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my $r;
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$r = sub {
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my ($s, $t) = @_;
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return unless $s && $t;
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node($op->(head($s), head($t)),
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promise { $r->(tail($s), tail($t)) });
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};
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}
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