parol 4.5.0

LL(k) and LALR(1) parser generator for Rust
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140

//! Grammar flow analysis
//! Productivity of non-terminals

use crate::grammar::symbol_string::SymbolString;
use crate::utils::{short_cut_conjunction_combine, short_cut_disjunction_combine};
use crate::{Cfg, Pr, Symbol};
use parol_runtime::log::trace;

/// Result type for each non-terminal:
/// true: productive
/// false: non-productive
type DomainType = bool;

/// The result vector applied to each iteration step;
/// is also returned after each iteration step
type ResultVector = Vec<DomainType>;

/// The type of the function in the equation system
/// It is called for each non-terminal
type TransferFunction<'a> = Box<dyn Fn(&ResultVector) -> DomainType + 'a>;

type EquationSystem<'a> = Vec<TransferFunction<'a>>;

type StepFunction = Box<dyn Fn(&EquationSystem, &ResultVector) -> ResultVector>;

/// Returns the non-productive terminals as a vector
pub fn non_productive_non_terminals(cfg: &Cfg) -> Vec<String> {
    // The indices within this vector of non-terminals corresponds to the indices in the result-vector.
    let non_terminals = cfg
        .get_non_terminal_set()
        .iter()
        .cloned()
        .collect::<Vec<String>>();

    let non_terminal_index =
        |nt: &str| -> usize { non_terminals.iter().position(|n| n == nt).unwrap() };

    let equation_system: EquationSystem = non_terminals.iter().fold(
        EquationSystem::with_capacity(non_terminals.len()),
        |mut es, nt| {
            let matching_productions = cfg.matching_productions(nt);
            es.push(combine_production_equation(
                matching_productions,
                non_terminal_index,
            ));
            es
        },
    );

    let step_function: StepFunction =
        Box::new(|es: &EquationSystem, result_vector: &ResultVector| {
            result_vector.iter().enumerate().fold(
                ResultVector::with_capacity(result_vector.len()),
                |mut acc, (i, _)| {
                    acc.push(es[i](result_vector));
                    acc
                },
            )
        });

    let mut result_vector = vec![false; non_terminals.len()];
    loop {
        let new_result_vector = step_function(&equation_system, &result_vector);
        trace!(
            "{}",
            trace_result_vector(&new_result_vector, &non_terminals)
        );
        if new_result_vector == result_vector {
            break;
        }
        result_vector = new_result_vector;
    }

    result_vector
        .iter()
        .enumerate()
        .fold(Vec::new(), |mut acc, (i, r)| {
            if !*r {
                acc.push(non_terminals[i].clone());
            }
            acc
        })
}

fn trace_result_vector(result_vector: &[bool], non_terminals: &[String]) -> String {
    result_vector
        .iter()
        .enumerate()
        .map(|(i, b)| format!("{}({})", non_terminals[i], if *b { "1" } else { "0" }))
        .collect::<Vec<String>>()
        .join(", ")
}

fn create_production_transfer_function<'a>(
    symbol_string: SymbolString,
    non_terminal_index: impl Fn(&str) -> usize + Clone,
) -> TransferFunction<'a> {
    let mut result_function: TransferFunction<'a> = Box::new(|_| true);
    for s in symbol_string.0 {
        if let Symbol::N(n, _, _, _) = s {
            let index = non_terminal_index(&n);
            let f = Box::new(move |result_vector: &ResultVector| result_vector[index]);
            result_function = Box::new(short_cut_conjunction_combine(result_function, f));
        }
    }
    result_function
}

fn combine_production_equation<'a, 'c>(
    matching_productions: Vec<(usize, &'c Pr)>,
    non_terminal_index: impl Fn(&str) -> usize + Clone,
) -> TransferFunction<'a> {
    if matching_productions.is_empty() {
        Box::new(|_| false)
    } else if matching_productions
        .iter()
        .any(|(_, p)| p.get_r().iter().all(|s| matches!(s, Symbol::T(_))))
    {
        Box::new(|_| true)
    } else {
        let mut symbol_strings =
            matching_productions
                .iter()
                .fold(Vec::new(), |mut acc, (_, pr)| {
                    acc.push((*pr).into());
                    acc
                });
        let mut prod_functions = symbol_strings
            .drain(..)
            .map(|symbol_string| {
                create_production_transfer_function(symbol_string, non_terminal_index.clone())
            })
            .collect::<Vec<TransferFunction<'a>>>();
        let mut result_function: TransferFunction<'a> = Box::new(|_| false);
        for f in prod_functions.drain(..) {
            result_function = Box::new(short_cut_disjunction_combine(result_function, f));
        }
        result_function
    }
}