Pkey access a key in an event stream

superclass: Pattern

Pkey simplifies backward access to values in an event being processed by Pbind or another event pattern.

*new(key)

The key is the name of the event variable to read from.

// \b should thus take twice the value of \a in each event:

p = Pbind(\a, Pwhite(1, 10, inf), \b, Pkey(\a) * 2).asStream;

p.next(()) // for Pbind, must pass in a default event even if empty

( 'a': 10, 'b': 20 )

( 'a': 2, 'b': 4 )

( 'a': 5, 'b': 10 )

( 'a': 4, 'b': 8 )

( 'a': 2, 'b': 4 )