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derivations.rs
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derivations.rs
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use liblet::derivation::derivation;
use liblet::grammar::grammar;
extern crate liblet;
// simple derivations usage starting from a grammar
fn main() {
// let's create our grammar first
let g = grammar(
"
Sentence -> Name | List End
List -> Name | Name , List
Name -> tom | dick | harry
, Name End -> and Name
",
);
// then create a derivation on it
let d = derivation(g);
// it does nothing by itself but we can make derivation
// steps on it, in order to get new sentential forms,
// based on the grammar production rules and the initial
// sentential form, which, by default, is the grammar start symbol
// we specify the production rule index and the index of the symbol
// in the sentential form from which to apply the derivation
let result = d.step(1, 0);
// notice that a derivation step could fail, so a Result is returned
assert!(result.is_ok());
let d = result.unwrap();
// we can now print out our derivation, which prints all the
// derivation steps done on the initial sentential form
// [Sentence -> Name]
println!("Derivation: {}", d);
// we can now do multiple steps at once, thanks to step
// returning a result containing the modified derivation as Ok
let result = d
.step(3, 0) // List End -> Name , List End
.and_then(|d| d.step(4, 0)) // Name , List End -> tom , List End
.and_then(|d| d.step(2, 2)) // tom , List End -> tom , Name End
.and_then(|d| d.step(7, 1)) // tom , Name End -> tom and Name
.and_then(|d| d.step(5, 2)); // tom and Name -> tom and dick
assert!(result.is_ok());
let d = result.unwrap();
println!("Derivation final: {}", d);
// at any time, you can query the derivation to get the
// derivation steps applied and the current sentential form
println!("Derivation steps: {:?}", d.steps());
println!("Derivation sentential form: {:?}", d.sentential_form());
}