plush genomes

The plush genome implemented here is an extension of that used in the Clojush system from Lee Spector’s lab at Hampshire College. In changing the representation and translation schemes, I’ve tried to maintain backwards-compatibility, but the Klapaucius Push dialect is no longer much like the Push found in Clojush, so be wary of breaking changes if you are importing Clojush genomes.

A plush genome is simply a vector of plush genes.

[TBD]

plush genes

A plush gene is a Clojure hash-map consisting of several key-value pairs, all optional:

1. :item: The value should be a Push literal to be inserted in the current cursor position in the program, or one of a few special editing commands (see below). Any :item that is not recognized as an editing command will be inserted into the program as found, unless it is nil.
2. :open: The value should be a positive integer which indicates how many branches should be opened immediately following the current insertion point. For example, {:item :x :open 1} will insert :x and an empty list at the current cursor position. {:item :x :open 3} will insert :x and an empty list, and set the translator up so that by the time translation is complete, a total of three lists will be inserted consecutively following the :x in the resulting program.
3. :close: The value should be a positive integer which indicates how many “pending” and current branches will be closed after the :item is inserted and any new branches created have been queued. For example, {:item :x :open 2 :close 1} will result in the insertion of :x, followed by an empty list (opened and then closed), and the beginning of a second list. Detailed examples are shown below, since I know this seems confusing.
4. :silent?: The value should be a true or false, indicating whether this gene should be processed or not. If true, no :item is inserted and no change to the branching state of the program is made: the entire gene is silenced.

Of these, none are strictly required. If :item is missing or nil, the gene can still modify the tree structure via the :open and :close fields. If :open is missing, then its value is assumed to be 0. If :close is missing, its value is also inferred to be 0. If :silent? is missing, its value is inferred to be false.

NOTE: In the original Clojush plush genome scheme used implementation-specific information about the Push language to implicitly calculate the :open value for each item. Specifically, the :open value was assumed to be the number of items from the :exec stack used by an instruction, or 0 otherwise. In the plush scheme, backwards-compatibility is available simply by setting the :open value explicitly to the same numerical value, and leaving it 0 or absent otherwise. That is, for each gene where the :item is a Push instruction, set an :open value equal to the number of :exec argument used by that instruction (which can be obtained via the helper function answer-factory.genome.plush/derived-push-branch-map).

editing commands

There are two plush-specific editing commands, which can appear as values in the :item field:

• :noop_delete_prev_paren_pair: This will “lift up” the contents of the last closed code block inserted (and closed), backtracking from the current cursor position.
• :noop_open_paren: This is included for backwards-compatibility with Clojush’s plush genome translator. It behaves exactly like the gene {:open 1}.

using a :branch-map argument

The plush->push function can accept an optional :branch-map argument, which should be a hash-map where the keys are one or more :item values, and the values are non-negative integers. The numeric values are used as a sort of “default” for the :open field of all genes in which the key is the :item. So for example when calling (plush->push [...genome...] :branch-map {:exec-dup 1 false 2} Every occurrence of a gene with {:item :exec-dup} will by default also include {:open 1}, and every gene with {:item false} will by default also include {:open 2}.

When no :branch-map is specified, the default :open value for every item is assumed to be 0. Whenever a gene explicitly specified an :open value, the default value in the :branch-map will be overridden for that gene, but will still apply to genes with the same :item and no explicit :open value elsewhere in the genome.

Some examples might be good

I’ve included some explicit examples in the form of runnable Midje facts, which show explicit examples of all this behavior.