| Working with the SPPF |
| ===================== |
|
|
| When parsing with Earley, Lark provides the ``ambiguity='forest'`` option |
| to obtain the shared packed parse forest (SPPF) produced by the parser as |
| an alternative to it being automatically converted to a tree. |
|
|
| Lark provides a few tools to facilitate working with the SPPF. Here are some |
| things to consider when deciding whether or not to use the SPPF. |
|
|
| **Pros** |
|
|
| - Efficient storage of highly ambiguous parses |
| - Precise handling of ambiguities |
| - Custom rule prioritizers |
| - Ability to handle infinite ambiguities |
| - Directly transform forest -> object instead of forest -> tree -> object |
|
|
| **Cons** |
|
|
| - More complex than working with a tree |
| - SPPF may contain nodes corresponding to rules generated internally |
| - Loss of Lark grammar features: |
|
|
| - Rules starting with '_' are not inlined in the SPPF |
| - Rules starting with '?' are never inlined in the SPPF |
| - All tokens will appear in the SPPF |
|
|
| SymbolNode |
| ---------- |
|
|
| .. autoclass:: lark.parsers.earley_forest.SymbolNode |
| :members: is_ambiguous, children |
|
|
| PackedNode |
| ---------- |
|
|
| .. autoclass:: lark.parsers.earley_forest.PackedNode |
| :members: children |
|
|
| ForestVisitor |
| ------------- |
|
|
| .. autoclass:: lark.parsers.earley_forest.ForestVisitor |
| :members: visit, visit_symbol_node_in, visit_symbol_node_out, |
| visit_packed_node_in, visit_packed_node_out, |
| visit_token_node, on_cycle, get_cycle_in_path |
|
|
| ForestTransformer |
| ----------------- |
|
|
| .. autoclass:: lark.parsers.earley_forest.ForestTransformer |
| :members: transform, transform_symbol_node, transform_intermediate_node, |
| transform_packed_node, transform_token_node |
|
|
| TreeForestTransformer |
| --------------------- |
|
|
| .. autoclass:: lark.parsers.earley_forest.TreeForestTransformer |
| :members: __default__, __default_token__, __default_ambig__ |
|
|
| handles_ambiguity |
| ----------------- |
|
|
| .. autofunction:: lark.parsers.earley_forest.handles_ambiguity |
|
|
