Ecosyste.ms: Awesome
An open API service indexing awesome lists of open source software.
https://github.com/fnogatz/dcg4pt
Extend Definite Clause Grammars for Prolog by the corresponding parse tree
https://github.com/fnogatz/dcg4pt
definite-clause-grammar grammar parsing prolog
Last synced: 19 days ago
JSON representation
Extend Definite Clause Grammars for Prolog by the corresponding parse tree
- Host: GitHub
- URL: https://github.com/fnogatz/dcg4pt
- Owner: fnogatz
- License: mit
- Created: 2018-10-23T14:48:55.000Z (about 6 years ago)
- Default Branch: main
- Last Pushed: 2023-01-20T11:03:38.000Z (almost 2 years ago)
- Last Synced: 2024-04-08T19:13:11.096Z (7 months ago)
- Topics: definite-clause-grammar, grammar, parsing, prolog
- Language: Prolog
- Homepage:
- Size: 35.2 KB
- Stars: 6
- Watchers: 2
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# DCGs for Parse Trees
Extend Definite Clause Grammars (DCG) for Prolog by an additional argument to automatically store the parse tree.
## Synopsis
```prolog
:- use_module(library(dcg4pt/expand)).
% Extended DCGs get expanded to hold an additional
% argument with parse tree.
sentence --> noun_phrase(N), verb_phrase(N).
noun_phrase(N) --> determiner, noun(N).
verb_phrase(N) --> ( verb(N) ; verb(N), noun_phrase(_) ).
noun(sg) --> [boy] ; [apple].
noun(pl) --> [boys] ; [apples].
determiner --> [the].
verb(sg) --> [eats].
verb(pl) --> [eat].
main :-
phrase(sentence(Tree), [the, boy, eats, the, apples]),
print_term(Tree, [indent_arguments(2)]).
% prints:
% sentence([
% noun_phrase([
% determiner(the),
% noun(boy) ]),
% verb_phrase([
% verb(eats),
% noun_phrase([
% determiner(the),
% noun(apples) ]) ]) ])
```
## Installation
This pack is available from the [add-on registry of SWI-Prolog](http://www.swi-prolog.org/pack/list).
It can be installed with `pack_install/1`:
```prolog
?- pack_install(dcg4pt).
```
## Requirements
Only for development purposes the [`tap` pack](http://www.swi-prolog.org/pack/list?p=tap) is needed:
```prolog
?- pack_install(tap).
```
## DCG Expansion
In most cases you simply want to automatically expand all given DCGs with the additional parse tree argument. To do so, simply call:
```prolog
:- use_module(library(dcg4pt/expand)).
% and later the definition of DCGs
```
Additionally you can manually call the predicates to translate a DCG4PT rule:
```prolog
?- use_module(library(dcg4pt)).
?- dcg4pt_rule_to_dcg_rule((sentence --> noun_phrase, verb_phrase), DCG).
DCG = (sentence(X) --> ( ... )).
```
## Usage
You can use the generated predicates like normal DCGs, besides that they provide an additional argument to hold the parse tree. It is automatically added as the very last argument of the DCG body.
### Bound Arguments
`library(dcg4pt)` has been implemented to provide a tool that generates a parse tree from a given input list but also the other way around, i.e., to generate a list based on a parse tree. So you can also use it this way:
```prolog
?- Tree = noun_phrase([determiner(the), noun(boy)]),
phrase(noun_phrase(N, Tree), List).
Tree = noun_phrase([determiner(the), noun(boy)]),
N = sg,
List = [the, boy] .
```
### Sequences
`library(dcg4pt)` provides a built-in `sequence(+Quantifier, :Body)` DCG body to resolve sequences of `Body` with the quantifiers `'?'`, `'+'`, and `'*'` as known from regular expressions. Their occurrences are represented as (possibly empty) lists in the parse tree:
```prolog
:- use_module(library(dcg4pt/expand)).
single --> [a].
list --> sequence('*', single).
non_empty_list --> sequence('+', single).
optional --> sequence('?', single).
main :-
phrase(list(Tree), [a, a, a]),
print_term(Tree, [indent_arguments(2)]).
% prints:
% list([
% single(a),
% single(a),
% single(a) ])
```
With a free variable given as the parse tree, the possibilities are generated beginning with the smallest solution:
```prolog
?- phrase(non_empty_list(Tree), List).
Tree = non_empty_list([single(a)]),
List = [a] ;
Tree = non_empty_list([single(a), single(a)]),
List = [a, a] ;
...
```