choice_maps.md

Choice Maps

Maps from the addresses of random choices to their values are stored in associative tree-structured data structures that have the following abstract type:

ChoiceMap

Choice maps are constructed by users to express observations and/or constraints on the traces of generative functions. Choice maps are also returned by certain Gen inference methods, and are used internally by various Gen inference methods.

Choice maps provide the following methods:

has_value
get_value
get_submap
get_values_shallow
get_submaps_shallow
to_array
from_array
get_selected

Note that none of these methods mutate the choice map.

Choice maps also implement:

• Base.isempty, which tests of there are no random choices in the choice map

• Base.merge, which takes two choice maps, and returns a new choice map containing all random choices in either choice map. It is an error if the choice maps both have values at the same address, or if one choice map has a value at an address that is the prefix of the address of a value in the other choice map.

• ==, which tests if two choice maps have the same addresses and values at those addresses.

DynamicChoiceMap
EmptyChoiceMap
StaticChoiceMap
choicemap

A mutable choice map can be constructed with choicemap, and then populated:

choices = choicemap()
choices[:x] = true
choices["foo"] = 1.25
choices[:y => 1 => :z] = -6.3

There is also a constructor that takes initial (address, value) pairs:

choices = choicemap((:x, true), ("foo", 1.25), (:y => 1 => :z, -6.3))

set_value!
set_submap!
Base.merge(::ChoiceMap, ::ChoiceMap)
Base.merge(::ChoiceMap, ::Vararg{ChoiceMap})
Base.isempty(::ChoiceMap)

Gen.pair
Gen.unpair
Gen.ChoiceMapNestedView