105 lines
2.6 KiB
Rust
105 lines
2.6 KiB
Rust
//! Characters
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//!
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//! Utilities for dealing with chars of various sorts.
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use std::collections::HashSet;
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use std::iter::FromIterator;
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pub type CharSet = HashSet<char>;
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// TODO: Use std::sync::Once for these sets?
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// https://doc.rust-lang.org/beta/std/sync/struct.Once.html
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fn ascii_letters() -> CharSet {
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let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".chars();
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CharSet::from_iter(letters)
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}
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fn ascii_digits() -> CharSet {
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let digits = "1234567890".chars();
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CharSet::from_iter(digits)
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}
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/// A set of all characters allowed to start Scheme identifiers.
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pub fn identifier_initials() -> CharSet {
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let letters = ascii_letters();
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let extras = CharSet::from_iter("!$%&*/:<=>?~_^".chars());
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let mut initials = CharSet::new();
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initials.extend(letters.iter());
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initials.extend(extras.iter());
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initials
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}
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/// A set of all characters allowed to follow an identifier initial.
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pub fn identifier_subsequents() -> CharSet {
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let initials = identifier_initials();
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let digits = ascii_digits();
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let extras = CharSet::from_iter(".+-".chars());
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let mut subsequents = CharSet::new();
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subsequents.extend(initials.iter());
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subsequents.extend(digits.iter());
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subsequents.extend(extras.iter());
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subsequents
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}
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//
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// char
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//
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pub trait Lexable {
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fn is_left_paren(&self) -> bool;
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fn is_right_paren(&self) -> bool;
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fn is_identifier_initial(&self) -> bool;
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fn is_identifier_subsequent(&self) -> bool;
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}
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impl Lexable for char {
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fn is_left_paren(&self) -> bool {
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self == &'('
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}
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fn is_right_paren(&self) -> bool {
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self == &')'
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}
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fn is_identifier_initial(&self) -> bool {
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identifier_initials().contains(&self)
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}
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fn is_identifier_subsequent(&self) -> bool {
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identifier_subsequents().contains(&self)
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}
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}
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//
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// str and String
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//
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pub trait RelativeIndexable {
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fn index_before(&self, &usize) -> Option<usize>;
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fn index_after(&self, &usize) -> Option<usize>;
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}
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impl RelativeIndexable for str {
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fn index_before(&self, index: &usize) -> Option<usize> {
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let mut prev_index = index - 1;
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if prev_index <= 0 {
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return None;
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}
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while !self.is_char_boundary(prev_index) {
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prev_index -= 1;
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}
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Some(prev_index)
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}
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fn index_after(&self, index: &usize) -> Option<usize> {
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let mut next_index = index + 1;
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if next_index >= self.len() {
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return None;
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}
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while !self.is_char_boundary(next_index) {
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next_index += 1;
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}
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Some(next_index)
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}
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}
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