int-seq 0.1.1

A procedural macro for generating integer sequences
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

use core::ops::Range;

use proc_macro::{TokenStream, TokenTree};

pub struct Parser {
    tokens: Vec<TokenTree>,
    idx: usize,
}

impl Parser {
    fn new(token_stream: TokenStream) -> Self {
        Self {
            tokens: token_stream.into_iter().collect::<Vec<_>>(),
            idx: 0,
        }
    }

    fn peek(&self) -> Option<TokenTree> {
        self.tokens.get(self.idx).cloned()
    }

    fn step(&mut self) {
        self.idx += 1;
    }

    fn step_back(&mut self) {
        self.idx -= 1;
    }

    fn munch_integer(&mut self) -> Option<i128> {
        let is_negative = self.munch_punct('-').is_some();
        let parity = if is_negative { -1 } else { 1 };

        match self.peek() {
            Some(TokenTree::Literal(lit)) => {
                self.step();
                let int_str = lit.to_string();
                let num: i128 = int_str
                    .parse()
                    .unwrap_or_else(|_| panic!("unable to parse {:?} as integer", int_str));
                Some(num * parity)
            }
            _ => None,
        }
    }

    fn munch_punct(&mut self, ch: char) -> Option<()> {
        match self.peek() {
            Some(TokenTree::Punct(punct)) if punct.as_char() == ch => {
                self.step();
                Some(())
            }
            _ => None,
        }
    }

    fn munch_range(&mut self) -> Option<Range<i128>> {
        let start = self.munch_integer()?;
        self.munch_punct('.')?;
        self.munch_punct('.')?;

        let inclusive = self.munch_punct('=').is_some();

        let end = self.munch_integer()?;
        Some(start..(end + if inclusive { 1 } else { 0 }))
    }
}

/// Parse ast of the form:
///  - `1..128`
///  - `1,2,4,8,16..128`
///  - `1,2,4,8,16..=128`
pub(crate) fn parse_int_seq(token_stream: &TokenStream) -> Option<(Vec<i128>, i128)> {
    let mut parser = Parser::new(token_stream.clone());
    let mut seq = Vec::new();

    // repeatedly munch integer + comma (`a,'+)
    while let Some(x) = parser.munch_integer() {
        seq.push(x);
        if parser.munch_punct(',').is_none() {
            let x = seq.pop().unwrap();
            parser.step_back();
            // also step back for the negative sign
            // this is very hacky. probably should have a separate lexing step
            if x < 0 {
                parser.step_back();
            }
            break;
        }
    }
    // munch range (`b..c` | `b..=c`)
    let range = parser.munch_range()?;

    seq.push(range.start);
    let end = range.end;
    Some((seq, end))
}