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predicate = ()
# Detect when a predicate becomes true.
# @category Liquidsoap
# @param ~init Detect at beginning.
# @param p Predicate.
def predicate.activates(~init=false, p)
last = ref(not init)
fun () -> begin
cur = p()
ans = (not !last) and cur
last := cur
ans
end
end
# Become true once every time a predicate is true.
# @category Liquidsoap
# @param p Predicate.
def predicate.once(p)
predicate.activates(init=true, p)
end
# Limit the number of times a predicate is true is a row.
# @param n Number of times the predicate is allowed to be true.
# @param p Predicate.
def predicate.at_most(n, p)
k = ref(0)
fun () -> begin
if p() then
ref.incr(k)
!k <= n
else
k := 0
false
end
end
end
# Detect when a predicate changes.
# @category Liquidsoap
# @param p Predicate.
def predicate.changes(p)
last = ref(p())
fun () -> begin
cur = p()
ans = (cur != !last)
last := cur
ans
end
end
# First occurrence of a predicate.
# @category Liquidsoap
# @param p Predicate.
def predicate.first(p)
done = ref(false)
fun () -> begin
if !done then
false
else
if p() then
done := true
true
else
false
end
end
end
end
# Predicate which is true when a signal is sent. The returned predicate has a
# method `signal` to send the signal.
# @category Liquidsoap
# @method signal Send a signal.
def predicate.signal()
state = ref(false)
def signal()
state := true
end
def p ()
if !state then
state := false
true
else
false
end
end
p.{ signal=signal }
end
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