Here's a REPL session, wherein I try to use "realized?" on a
lazy-seq.
Clojure 1.3.0
Define the lazy-seq:
user=> (def naturals (iterate inc 0))
#'user/naturals
Force realization of the first 1 + 123456 elements:
user=> (time (nth naturals 123456))
"Elapsed time: 481.349 msecs"
123456
Due to previous realization, the same expression now eval's
quickly:
user=> (time (nth naturals 123456))
"Elapsed time: 15.571 msecs"
123456
Now I try to use "realized?" on 123456th element:
user=> (realized? (nth naturals 123456))
ClassCastException java.lang.Long cannot be cast to
clojure.lang.IPending clojure.core/realized? (core.clj:6505)
Ouch! I guess "realized?" isn't a macro. Next try:
user=> (realized? (drop 123456 naturals))
false
Hmmm... could I be off by one? Let's leave lots of room for error:
user=> (realized? (drop 12345 naturals))
false
user=> (realized? (drop 0 naturals))
false
Huh? How do I get "realized?" to tell me what I want to know?
What I want to know, is wether the element at the nth index
has been computed and cached. Maybe something like "realized-
length", just for lazy-seq's, which would report how far along
the sequence has realization occurred.
Thanks,
George Kangas
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