Codify and Resolve modifiers

build.rs

@@ -2,8 +2,13 @@ use std::fmt::Write;
 use std::iter::Peekable;
 use std::path::Path;
 
+use self::shared::ModifierSet;
+
 type StrResult<T> = Result<T, String>;
 
+#[path = "src/shared.rs"]
+mod shared;
+
 /// A module of definitions.
 struct Module<'a>(Vec<(&'a str, Binding<'a>)>);
 
@@ -29,7 +34,7 @@ enum Def<'a> {
 /// A symbol, either a leaf or with modifiers.
 enum Symbol<'a> {
     Single(char),
-    Multi(Vec<(&'a str, char)>),
+    Multi(Vec<(ModifierSet<&'a str>, char)>),
 }
 
 /// A single line during parsing.
@@ -40,7 +45,7 @@ enum Line<'a> {
     ModuleStart(&'a str),
     ModuleEnd,
     Symbol(&'a str, Option<char>),
-    Variant(&'a str, char),
+    Variant(ModifierSet<&'a str>, char),
 }
 
 fn main() {
@@ -110,7 +115,7 @@ fn tokenize(line: &str) -> StrResult<Line> {
             validate_ident(part)?;
         }
         let c = decode_char(tail.ok_or("missing char")?)?;
-        Line::Variant(rest, c)
+        Line::Variant(ModifierSet::new_unchecked(rest), c)
     } else {
         validate_ident(head)?;
         let c = tail.map(decode_char).transpose()?;
@@ -167,7 +172,7 @@ fn parse<'a>(
 
                 let symbol = if variants.len() > 0 {
                     if let Some(c) = c {
-                        variants.insert(0, ("", c));
+                        variants.insert(0, (ModifierSet::default(), c));
                     }
                     Symbol::Multi(variants)
                 } else {

src/lib.rs

@@ -1,6 +1,15 @@
-/*!
-Human-friendly notation for Unicode symbols.
-*/
+//! Human-friendly notation for Unicode symbols.
+//!
+//! ## Model
+//! A [`Symbol`] is a collection of one or more _variants_. Each variant is
+//! identified by a set of [_modifiers_](ModifierSet) and has a single character
+//! as its value. The modifiers themselves can in principle be any non-empty
+//! strings that don't contain the character `.`, but codex only defines ones
+//! that are entirely made of ASCII alphabetical characters.
+
+pub use self::shared::ModifierSet;
+
+mod shared;
 
 /// A module of definitions.
 #[derive(Debug, Copy, Clone)]
@@ -52,7 +61,41 @@ pub enum Symbol {
     /// A symbol without modifiers.
     Single(char),
     /// A symbol with named modifiers. The symbol defaults to its first variant.
-    Multi(&'static [(&'static str, char)]),
+    Multi(&'static [(ModifierSet<&'static str>, char)]),
+}
+
+impl Symbol {
+    /// Get the symbol's character for a given set of modifiers.
+    pub fn get(&self, modifs: ModifierSet<&str>) -> Option<char> {
+        match self {
+            Self::Single(c) => modifs.is_empty().then_some(*c),
+            Self::Multi(list) => modifs.best_match_in(list.iter().copied()),
+        }
+    }
+
+    /// The characters that are covered by this symbol.
+    pub fn variants(&self) -> impl Iterator<Item = (ModifierSet<&str>, char)> {
+        enum Variants {
+            Single(std::iter::Once<char>),
+            Multi(std::slice::Iter<'static, (ModifierSet<&'static str>, char)>),
+        }
+        let mut iter = match self {
+            Self::Single(c) => Variants::Single(std::iter::once(*c)),
+            Self::Multi(sl) => Variants::Multi(sl.iter()),
+        };
+        std::iter::from_fn(move || match &mut iter {
+            Variants::Single(iter) => Some((ModifierSet::default(), iter.next()?)),
+            Variants::Multi(iter) => iter.next().copied(),
+        })
+    }
+
+    /// Possible modifiers for this symbol.
+    pub fn modifiers(&self) -> impl Iterator<Item = &str> + '_ {
+        self.variants()
+            .flat_map(|(m, _)| m.into_iter())
+            .collect::<std::collections::BTreeSet<_>>()
+            .into_iter()
+    }
 }
 
 /// A module that contains the other top-level modules.

src/shared.rs

@@ -0,0 +1,228 @@
+use std::ops::Deref;
+
+/// A set of modifiers.
+///
+/// Beware: The [`Eq`] and [`Hash`] implementations are dependent on the
+/// ordering of the modifiers, in opposition to what a set would usually
+/// constitute. To test for set-wise equality, use [`iter`](Self::iter) and
+/// collect into a true set type like [`HashSet`](std::collections::HashSet).
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct ModifierSet<S>(
+    // Note: the visibility needs to be `pub(crate)`, since build.rs outputs
+    // `ModifierSet(...)`.
+    pub(crate) S,
+);
+
+impl<S: Deref<Target = str>> ModifierSet<S> {
+    /// Constructs a modifier set from a string, where modifiers are separated by
+    /// the character `.`.
+    ///
+    /// It is not unsafe to use this function wrongly, but it can produce
+    /// unexpected results down the line. Correct usage should ensure that `s`
+    /// does not contain any empty modifiers (i.e. the sequence `..`) and that
+    /// no modifier occurs twice.
+    pub fn new_unchecked(s: S) -> Self {
+        Self(s)
+    }
+
+    /// Whether `self` is empty.
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+
+    /// Gets the string of modifiers separated by `.`.
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
+
+    /// Converts the underlying string to a slice.
+    pub fn as_deref(&self) -> ModifierSet<&str> {
+        ModifierSet(&self.0)
+    }
+
+    /// Add a modifier to the set, without checking that it is a valid modifier.
+    ///
+    /// It is not unsafe to use this method wrongly, but that can produce
+    /// unexpected results down the line. Correct usage should ensure that
+    /// `modifier` is not empty and doesn't contain the character `.`.
+    pub fn add_unchecked(&mut self, m: &str)
+    where
+        S: for<'a> std::ops::AddAssign<&'a str>,
+    {
+        if !self.0.is_empty() {
+            self.0 += ".";
+        }
+        self.0 += m;
+    }
+
+    /// Iterates over the list of modifiers in an arbitrary order.
+    pub fn iter(&self) -> impl Iterator<Item = &str> {
+        self.into_iter()
+    }
+
+    /// Whether the set contains the modifier `m`.
+    pub fn contains(&self, m: &str) -> bool {
+        self.iter().any(|lhs| lhs == m)
+    }
+
+    /// Finds the best match from the list.
+    ///
+    /// To be considered a match, the modifier set must be a superset of
+    /// (or equal to) `self`. Among different matches, the best one is selected
+    /// by the following two criteria (in order):
+    /// 1. Number of modifiers in common with `self` (more is better).
+    /// 2. Total number of modifiers (fewer is better).
+    ///
+    /// If there are multiple best matches, the first of them is returned.
+    pub fn best_match_in<'a, T>(
+        &self,
+        variants: impl Iterator<Item = (ModifierSet<&'a str>, T)>,
+    ) -> Option<T> {
+        let mut best = None;
+        let mut best_score = None;
+
+        // Find the best table entry with this name.
+        for candidate in variants.filter(|(set, _)| self.is_subset(*set)) {
+            let mut matching = 0;
+            let mut total = 0;
+            for modifier in candidate.0.iter() {
+                if self.contains(modifier) {
+                    matching += 1;
+                }
+                total += 1;
+            }
+
+            let score = (matching, std::cmp::Reverse(total));
+            if best_score.is_none_or(|b| score > b) {
+                best = Some(candidate.1);
+                best_score = Some(score);
+            }
+        }
+
+        best
+    }
+
+    /// Whether all modifiers in `self` are also present in `other`.
+    pub fn is_subset(&self, other: ModifierSet<&str>) -> bool {
+        self.iter().all(|m| other.contains(m))
+    }
+}
+
+impl<S: Default> Default for ModifierSet<S> {
+    /// Constructs the default modifier set.
+    ///
+    /// This is typically the empty set, though the remark from
+    /// [`Self::new_unchecked`] applies since `S::default()` could technically
+    /// be anything.
+    fn default() -> Self {
+        Self(S::default())
+    }
+}
+
+impl<'a, S: Deref<Target = str>> IntoIterator for &'a ModifierSet<S> {
+    type Item = &'a str;
+    type IntoIter = std::str::Split<'a, char>;
+
+    /// Iterate over the list of modifiers in an arbitrary order.
+    fn into_iter(self) -> Self::IntoIter {
+        let mut iter = self.0.split('.');
+        if self.0.is_empty() {
+            // empty the iterator
+            let _ = iter.next();
+        }
+        iter
+    }
+}
+
+impl<'a> IntoIterator for ModifierSet<&'a str> {
+    type Item = &'a str;
+    type IntoIter = std::str::Split<'a, char>;
+
+    /// Iterate over the list of modifiers in an arbitrary order.
+    fn into_iter(self) -> Self::IntoIter {
+        let mut iter = self.0.split('.');
+        if self.0.is_empty() {
+            // empty the iterator
+            let _ = iter.next();
+        }
+        iter
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    type ModifierSet = super::ModifierSet<&'static str>;
+
+    #[test]
+    fn default_is_empty() {
+        assert!(ModifierSet::default().is_empty());
+    }
+
+    #[test]
+    fn iter_count() {
+        assert_eq!(ModifierSet::default().iter().count(), 0);
+        assert_eq!(ModifierSet::new_unchecked("a").iter().count(), 1);
+        assert_eq!(ModifierSet::new_unchecked("a.b").iter().count(), 2);
+        assert_eq!(ModifierSet::new_unchecked("a.b.c").iter().count(), 3);
+    }
+
+    #[test]
+    fn subset() {
+        assert!(
+            ModifierSet::new_unchecked("a").is_subset(ModifierSet::new_unchecked("a.b"))
+        );
+        assert!(
+            ModifierSet::new_unchecked("a").is_subset(ModifierSet::new_unchecked("b.a"))
+        );
+        assert!(ModifierSet::new_unchecked("a.b")
+            .is_subset(ModifierSet::new_unchecked("b.c.a")));
+    }
+
+    #[test]
+    fn best_match() {
+        // 1. more modifiers in common with self
+        assert_eq!(
+            ModifierSet::new_unchecked("a.b").best_match_in(
+                [
+                    (ModifierSet::new_unchecked("a.c"), 1),
+                    (ModifierSet::new_unchecked("a.b"), 2),
+                ]
+                .into_iter()
+            ),
+            Some(2)
+        );
+        // 2. fewer modifiers in general
+        assert_eq!(
+            ModifierSet::new_unchecked("a").best_match_in(
+                [
+                    (ModifierSet::new_unchecked("a"), 1),
+                    (ModifierSet::new_unchecked("a.b"), 2),
+                ]
+                .into_iter()
+            ),
+            Some(1)
+        );
+        // the first rule takes priority over the second
+        assert_eq!(
+            ModifierSet::new_unchecked("a.b").best_match_in(
+                [
+                    (ModifierSet::new_unchecked("a"), 1),
+                    (ModifierSet::new_unchecked("a.b"), 2),
+                ]
+                .into_iter()
+            ),
+            Some(2)
+        );
+        // among multiple best matches, the first one is returned
+        assert_eq!(
+            ModifierSet::default().best_match_in(
+                [
+                    (ModifierSet::new_unchecked("a"), 1),
+                    (ModifierSet::new_unchecked("b"), 2)
+                ]
+                .into_iter()
+            ),
+            Some(1)
+        );
+    }
+}