Functional Operations
How you can transform, combine and operate with sets in a functional way.
We explore the functional operations provided by Lasp. Each of these functions takes, as input, a single source collection and creates a single output collection. The output will be maintained as the input is modified, and these operators can be chained arbitrarily.
Map Operation
First, declare a source set.
> {ok, {SourceId, _, _, _}} = lasp:declare({<<"source">>, state_orset}, state_orset).
{ok,{{<<"source">>,state_orset},
state_orset,
[{clock,[{<<170,227,142,126,63,64,19,227,195,66,39,125,58,
195,75,134,148,109,168,...>>,
1}]}],
{state_orset,[]}}}
Then, declare a destination set.
> {ok, {DestinationId, _, _, _}} = lasp:declare({<<"destination">>, state_orset}, state_orset).
{ok,{{<<"destination">>,state_orset},
state_orset,
[{clock,[{<<170,227,142,126,63,64,19,227,195,66,39,125,58,
195,75,134,148,109,168,...>>,
1}]}],
{state_orset,[]}}}
Let's map the values from one set into the other, and double the elements.
> lasp:map(SourceId, fun(X) -> X * 2 end, DestinationId).
ok
Now, we can add an element to the first set and see the results of the transformation in the destination set!
> lasp:update(SourceId, {add, 1}, self()).
{ok,{{<<"source">>,state_orset},
state_orset,
[{clock,[{<<170,227,142,126,63,64,19,227,195,66,39,125,58,
195,75,134,148,109,168,...>>,
2}]}],
{state_orset,[{1,
[{<<124,101,224,70,103,26,222,240,141,97,96,128,120,143,
228,148,...>>,
true}]}]}}}
> lasp:query(DestinationId).
{ok,{set,1,16,16,8,80,48,
{[],[],[],[],[],[],[],[],[],[],[],[],[],[],[],[]},
{{[],[],[],[],[],[],[2],[],[],[],[],[],[],[],[],[]}}}}
> {ok, Result} = lasp:query(DestinationId), sets:to_list(Result).
[2]
Filter Operation
Now, assuming we still have the source set declared from the section above, we can apply a filter directly to it.
First, let's declare somewhere to store the results.
> {ok, {FilteredId, _, _, _}} = lasp:declare({<<"filtered">>, state_orset}, state_orset).
{ok,{{<<"filtered">>,state_orset},
state_orset,
[{clock,[{<<170,227,142,126,63,64,19,227,195,66,39,125,58,
195,75,134,148,109,168,...>>,
1}]}],
{state_orset,[]}}}
Now, let's apply a filter that only allows even elements through.
> lasp:filter(SourceId, fun(X) -> X rem 2 == 0 end, FilteredId).
ok
Since the source set only has 1 in it, the filtered set should be empty!
> {ok, Result1} = lasp:query(FilteredId), sets:to_list(Result1).
[]
But, if we add an element to the set that's even, we should see the output in the filtered set.
> lasp:update(SourceId, {add, 2}, self()). {ok,{{<<"source">>,state_orset},
state_orset,
[{clock,[{<<170,227,142,126,63,64,19,227,195,66,39,125,58,
195,75,134,148,109,168,...>>,
3}]}],
{state_orset,[{1,
[{<<124,101,224,70,103,26,222,240,141,97,96,128,120,143,
228,148,...>>,
true}]},
{2,
[{<<82,188,56,236,83,244,32,79,114,44,4,33,148,226,184,...>>,
true}]}]}}}
> {ok, Result2} = lasp:query(FilteredId), sets:to_list(Result2).
[2]
Fold Operation
We avoid discussion of the fold operation here, as it's currently being revised and the interface i the prototype is less than desirable at the current moment.
Updated less than a minute ago