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
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169

//! Lexing.

use crate::Symb;
use core::fmt::{self, Display};
use logos::{Filter, Lexer, Logos};

/// A token generated by the lexer.
#[derive(Logos, Debug, PartialEq, Eq)]
#[logos(type S = &str)]
pub enum Token<S> {
    /// definition
    #[token("def")]
    Def,

    /// theorem
    #[token("thm")]
    Thm,

    /// opening bracket
    #[token("[")]
    LBrk,

    /// closing bracket
    #[token("]")]
    RBrk,

    /// opening parenthesis
    #[token("(")]
    LPar,

    /// closing parenthesis
    #[token(")")]
    RPar,

    /// has type
    #[token(":")]
    Colon,

    /// is defined as
    #[token(":=")]
    ColonEq,

    /// product
    #[token("->")]
    Arrow,

    /// abstraction
    #[token("=>")]
    FatArrow,

    /// rewrites to
    #[token("-->")]
    LongArrow,

    /// separate variables in rewrite rule contexts
    #[token(",")]
    Comma,

    /// terminate command
    #[token(".")]
    Dot,

    /// symbol
    #[regex("[a-zA-Z0-9_!?][a-zA-Z0-9_!?']*", symb)]
    #[token("{|", moustache)]
    Symb(Symb<S>),

    /// unclosed comments (the number indicates how many comments are still open)
    #[token("(;", comment1)]
    Comment(usize),

    /// unrecognised token
    #[regex(r"[ \t\n\f]+", logos::skip)]
    #[error]
    Error,
}

impl<S: Display> Display for Token<S> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Self::Def => "def".fmt(f),
            Self::Thm => "thm".fmt(f),
            Self::LBrk => "[".fmt(f),
            Self::RBrk => "]".fmt(f),
            Self::LPar => "(".fmt(f),
            Self::RPar => ")".fmt(f),
            Self::Colon => ":".fmt(f),
            Self::ColonEq => ":=".fmt(f),
            Self::Arrow => "->".fmt(f),
            Self::FatArrow => "=>".fmt(f),
            Self::LongArrow => "-->".fmt(f),
            Self::Comma => ",".fmt(f),
            Self::Dot => ".".fmt(f),
            Self::Symb(s) => s.fmt(f),
            Self::Comment(_) => " ".fmt(f),
            Self::Error => Err(Default::default()),
        }
    }
}

fn symb<'s>(lex: &mut Lexer<'s, Token<&'s str>>) -> Option<Symb<&'s str>> {
    let mut symb = Symb::new(lex.slice());

    // regular expressions for head and tail of identifiers
    let ih = |c| matches!(c, 'a' ..= 'z' | 'A' ..= 'Z' | '0' ..= '9' | '_' | '!' | '?');
    let it = |c| matches!(c, 'a' ..= 'z' | 'A' ..= 'Z' | '0' ..= '9' | '_' | '!' | '?' | '\'');

    while let Some(after_dot) = lex.remainder().strip_prefix('.') {
        let len = if let Some(tail) = after_dot.strip_prefix(ih) {
            1 + tail.find(|c| !it(c)).unwrap_or(tail.len())
        } else if let Some(after_moustache) = after_dot.strip_prefix("{|") {
            2 + after_moustache.find("|}")? + 2
        } else {
            break;
        };

        symb.push(&after_dot[..len]);
        lex.bump(1 + len); // eat the dot
    }

    Some(symb)
}

fn moustache<'s>(lex: &mut Lexer<'s, Token<&'s str>>) -> Option<Symb<&'s str>> {
    let len = lex.remainder().find("|}")?;
    lex.bump(len + 2); // include len of `|}`
    symb(lex)
}

fn comment1<'s>(lex: &mut Lexer<'s, Token<&'s str>>) -> Filter<usize> {
    match comment(lex, 1) {
        0 => Filter::Skip,
        n => Filter::Emit(n),
    }
}

/// Lex inside a comment until end of comment or input, return number of open comments.
pub(crate) fn comment<'s>(lex: &mut Lexer<'s, Token<&'s str>>, mut open: usize) -> usize {
    let prefix: &[_] = &['(', ';'];
    while open > 0 {
        // go to first occurrence of either ';' or '('
        match lex.remainder().find(prefix) {
            Some(offset) => lex.bump(offset),
            None => {
                lex.bump(lex.remainder().len());
                return open;
            }
        };
        if lex.remainder().starts_with("(;") {
            open += 1;
            lex.bump(2);
        } else if lex.remainder().starts_with(";)") {
            open -= 1;
            lex.bump(2);
        } else {
            lex.bump(1);
        }
    }
    0
}

#[test]
fn comment_open() {
    let s = "opening .. (; closing .. ;) still one open ..";
    assert!(matches!(comment1(&mut Token::lexer(s)), Filter::Emit(1)));

    let s = "closing .. ;) none open";
    assert!(matches!(comment1(&mut Token::lexer(s)), Filter::Skip));
}