Kilian Sprotte wrote:
Hi,
I am rather an Oz newbie and I am having a little problem with the
Space hierarchy. I have written a function that returns some data (a
list of FS constants...) to be used in a search script - I have
implemented this function using a dictionary for memoization, because I
was hoping to access the desired data inside the search script without
being forced to precompute it explicitly beforehand. (Since outside the
search script, I dont really know what my args to this function are...)
I am getting an error that states I cannot do Dictionary.put from a
local Space.
Indeed, computation spaces normally cannot have side effects. Basically
if the arguments of your function are not chunks, you can store the
dictionary outside the space, using the technique you mention:
Wanted to ask you, if redesigning this memoized functions as an Active
Service using a port would probably solve the problem?
Imagine that F is the (unary) function that actually computes a result.
The function MemoF below returns the same results as F, and memoizes
them. MemoF can be used in subspaces if its argument is a number, or an
atom.
local
Memo={NewDictionary}
S P={NewPort S}
in
thread
for X#Y in S do
if {Not {Dictionary.isMember Memo X}}
then Y=Memo.X
else Y={F X} Memo.X:=Y
end
end
end
fun {MemoF X}
Y in {Port.sendRecv P X Y} Y
end
end
If you want to use more complex arguments, you'll need to either map
them to integers, or use a something more sophisticated than a
dictionary for the memo table.
Cheers,
raph
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