From type/Promise

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multi method break(Promise:D: \cause = False)

Breaks a promise, optionally setting the cause. If no cause is passed, the cause will be False.

Throws an exception of type X::Promise::Vowed if a vow has already been taken. See method vow for more information.

my $p = Promise.new;
 
$p.break('sorry');
say $p.status;          # OUTPUT: «Broken␤» 
say $p.cause;           # OUTPUT: «sorry␤»