Add Value type and replace dyn-nodes with call-exprs 🏗

- In addition to syntax trees there are now `Value`s, which syntax trees can be evaluated into (e.g. the tree is `5+5` and the value is `10`)
- Parsing is completely pure, function calls are not parsed into nodes, but into simple call expressions, which are resolved later
- Functions aren't dynamic nodes anymore, but simply functions which receive their arguments as a table and the layouting context
- Functions may return any `Value`
- Layouting is powered by functions which return the new `Commands` value, which informs the layouting engine what to do
- When a function returns a non-`Commands` value, the layouter simply dumps the value into the document in monospace

1 files changed, 379 insertions, 0 deletions

diff --git a/src/compute/table.rs b/src/compute/table.rs
new file mode 100644
index 00000000..f11eacfc
--- /dev/null
+++ b/src/compute/table.rs
@@ -0,0 +1,379 @@
+//! A key-value map that can also model array-like structures.
+
+use std::collections::BTreeMap;
+use std::fmt::{self, Debug, Formatter};
+use std::ops::Index;
+
+use crate::syntax::span::{Span, Spanned};
+
+/// A table data structure, which maps from integers (`u64`) or strings to a
+/// generic value type.
+///
+/// The table can be used to model arrays by assigns values to successive
+/// indices from `0..n`. The table type offers special support for this pattern
+/// through the `push` method.
+#[derive(Clone)]
+pub struct Table<V> {
+    nums: BTreeMap<u64, V>,
+    strs: BTreeMap<String, V>,
+    lowest_free: u64,
+}
+
+impl<V> Table<V> {
+    /// Create a new empty table.
+    pub fn new() -> Self {
+        Self {
+            nums: BTreeMap::new(),
+            strs: BTreeMap::new(),
+            lowest_free: 0,
+        }
+    }
+
+    /// The total number of entries in the table.
+    pub fn len(&self) -> usize {
+        self.nums.len() + self.strs.len()
+    }
+
+    /// Whether the table contains no entries.
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// The first number key-value pair (with lowest number).
+    pub fn first(&self) -> Option<(u64, &V)> {
+        self.nums.iter().next().map(|(&k, v)| (k, v))
+    }
+
+    /// The last number key-value pair (with highest number).
+    pub fn last(&self) -> Option<(u64, &V)> {
+        self.nums.iter().next_back().map(|(&k, v)| (k, v))
+    }
+
+    /// Get a reference to the value with the given key.
+    pub fn get<'a, K>(&self, key: K) -> Option<&V>
+    where
+        K: Into<BorrowedKey<'a>>,
+    {
+        match key.into() {
+            BorrowedKey::Num(num) => self.nums.get(&num),
+            BorrowedKey::Str(string) => self.strs.get(string),
+        }
+    }
+
+    /// Borrow the value with the given key mutably.
+    pub fn get_mut<'a, K>(&mut self, key: K) -> Option<&mut V>
+    where
+        K: Into<BorrowedKey<'a>>,
+    {
+        match key.into() {
+            BorrowedKey::Num(num) => self.nums.get_mut(&num),
+            BorrowedKey::Str(string) => self.strs.get_mut(string),
+        }
+    }
+
+    /// Insert a value into the table.
+    pub fn insert<K>(&mut self, key: K, value: V)
+    where
+        K: Into<OwnedKey>,
+    {
+        match key.into() {
+            OwnedKey::Num(num) => {
+                self.nums.insert(num, value);
+                if self.lowest_free == num {
+                    self.lowest_free += 1;
+                }
+            }
+            OwnedKey::Str(string) => {
+                self.strs.insert(string, value);
+            }
+        }
+    }
+
+    /// Remove the value with the given key from the table.
+    pub fn remove<'a, K>(&mut self, key: K) -> Option<V>
+    where
+        K: Into<BorrowedKey<'a>>,
+    {
+        match key.into() {
+            BorrowedKey::Num(num) => {
+                self.lowest_free = self.lowest_free.min(num);
+                self.nums.remove(&num)
+            }
+            BorrowedKey::Str(string) => self.strs.remove(string),
+        }
+    }
+
+    /// Append a value to the table.
+    ///
+    /// This will associate the `value` with the lowest free number key (zero if
+    /// there is no number key so far).
+    pub fn push(&mut self, value: V) {
+        while self.nums.contains_key(&self.lowest_free) {
+            self.lowest_free += 1;
+        }
+        self.nums.insert(self.lowest_free, value);
+        self.lowest_free += 1;
+    }
+
+    /// Iterate over the number key-value pairs.
+    pub fn nums(&self) -> std::collections::btree_map::Iter<u64, V> {
+        self.nums.iter()
+    }
+
+    /// Iterate over the string key-value pairs.
+    pub fn strs(&self) -> std::collections::btree_map::Iter<String, V> {
+        self.strs.iter()
+    }
+
+    /// Iterate over all values in the table.
+    pub fn values(&self) -> impl Iterator<Item = &V> {
+        self.nums().map(|(_, v)| v).chain(self.strs().map(|(_, v)| v))
+    }
+
+    /// Iterate over the number key-value pairs.
+    pub fn into_nums(self) -> std::collections::btree_map::IntoIter<u64, V> {
+        self.nums.into_iter()
+    }
+
+    /// Iterate over the string key-value pairs.
+    pub fn into_strs(self) -> std::collections::btree_map::IntoIter<String, V> {
+        self.strs.into_iter()
+    }
+
+    /// Move into an owned iterator over all values in the table.
+    pub fn into_values(self) -> impl Iterator<Item = V> {
+        self.nums.into_iter().map(|(_, v)| v)
+            .chain(self.strs.into_iter().map(|(_, v)| v))
+    }
+}
+
+impl<'a, K, V> Index<K> for Table<V>
+where
+    K: Into<BorrowedKey<'a>>,
+{
+    type Output = V;
+
+    fn index(&self, index: K) -> &Self::Output {
+        self.get(index).expect("key not in table")
+    }
+}
+
+impl<V> Default for Table<V> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<V: Eq> Eq for Table<V> {}
+
+impl<V: PartialEq> PartialEq for Table<V> {
+    fn eq(&self, other: &Self) -> bool {
+        self.nums().eq(other.nums()) && self.strs().eq(other.strs())
+    }
+}
+
+impl<V: Debug> Debug for Table<V> {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        if self.is_empty() {
+            return f.write_str("()");
+        }
+
+        let mut builder = f.debug_tuple("");
+
+        struct Entry<'a>(&'a dyn Debug, &'a dyn Debug);
+        impl<'a> Debug for Entry<'a> {
+            fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+                self.0.fmt(f)?;
+                if f.alternate() {
+                    f.write_str(" = ")?;
+                } else {
+                    f.write_str("=")?;
+                }
+                self.1.fmt(f)
+            }
+        }
+
+        for (key, value) in self.nums() {
+            builder.field(&Entry(&key, &value));
+        }
+
+        for (key, value) in self.strs() {
+            builder.field(&Entry(&key, &value));
+        }
+
+        builder.finish()
+    }
+}
+
+/// The owned variant of a table key.
+#[derive(Debug, Clone, Eq, PartialEq, Ord, PartialOrd)]
+pub enum OwnedKey {
+    Num(u64),
+    Str(String),
+}
+
+impl From<u64> for OwnedKey {
+    fn from(num: u64) -> Self {
+        Self::Num(num)
+    }
+}
+
+impl From<String> for OwnedKey {
+    fn from(string: String) -> Self {
+        Self::Str(string)
+    }
+}
+
+impl From<&'static str> for OwnedKey {
+    fn from(string: &'static str) -> Self {
+        Self::Str(string.to_string())
+    }
+}
+
+/// The borrowed variant of a table key.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
+pub enum BorrowedKey<'a> {
+    Num(u64),
+    Str(&'a str),
+}
+
+impl From<u64> for BorrowedKey<'static> {
+    fn from(num: u64) -> Self {
+        Self::Num(num)
+    }
+}
+
+impl<'a> From<&'a String> for BorrowedKey<'a> {
+    fn from(string: &'a String) -> Self {
+        Self::Str(&string)
+    }
+}
+
+impl<'a> From<&'a str> for BorrowedKey<'a> {
+    fn from(string: &'a str) -> Self {
+        Self::Str(string)
+    }
+}
+
+/// An table entry which tracks key and value span.
+#[derive(Clone, PartialEq)]
+pub struct SpannedEntry<V> {
+    pub key: Span,
+    pub val: Spanned<V>,
+}
+
+impl<V> SpannedEntry<V> {
+    /// Create a new entry.
+    pub fn new(key: Span, val: Spanned<V>) -> Self {
+        Self { key, val }
+    }
+
+    /// Create an entry with the same span for key and value.
+    pub fn val(val: Spanned<V>) -> Self {
+        Self { key: Span::ZERO, val }
+    }
+
+    /// Convert from `&SpannedEntry<T>` to `SpannedEntry<&T>`
+    pub fn as_ref(&self) -> SpannedEntry<&V> {
+        SpannedEntry { key: self.key, val: self.val.as_ref() }
+    }
+
+    /// Map the entry to a different value type.
+    pub fn map<U>(self, f: impl FnOnce(V) -> U) -> SpannedEntry<U> {
+        SpannedEntry { key: self.key, val: self.val.map(f) }
+    }
+}
+
+impl<V: Debug> Debug for SpannedEntry<V> {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        if f.alternate() {
+            f.write_str("key")?;
+            self.key.fmt(f)?;
+            f.write_str(" ")?;
+        }
+        self.val.fmt(f)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Table;
+
+    #[test]
+    fn test_table_different_key_types_dont_interfere() {
+        let mut table = Table::new();
+        table.insert(10, "hello");
+        table.insert("twenty", "there");
+        assert_eq!(table.len(), 2);
+        assert_eq!(table[10], "hello");
+        assert_eq!(table["twenty"], "there");
+    }
+
+    #[test]
+    fn test_table_push_skips_already_inserted_keys() {
+        let mut table = Table::new();
+        table.insert(2, "2");
+        table.push("0");
+        table.insert(3, "3");
+        table.push("1");
+        table.push("4");
+        assert_eq!(table.len(), 5);
+        assert_eq!(table[0], "0");
+        assert_eq!(table[1], "1");
+        assert_eq!(table[2], "2");
+        assert_eq!(table[3], "3");
+        assert_eq!(table[4], "4");
+    }
+
+    #[test]
+    fn test_table_push_remove_push_reuses_index() {
+        let mut table = Table::new();
+        table.push("0");
+        table.push("1");
+        table.push("2");
+        table.remove(1);
+        table.push("a");
+        table.push("3");
+        assert_eq!(table.len(), 4);
+        assert_eq!(table[0], "0");
+        assert_eq!(table[1], "a");
+        assert_eq!(table[2], "2");
+        assert_eq!(table[3], "3");
+    }
+
+    #[test]
+    fn test_table_first_and_last_are_correct() {
+        let mut table = Table::new();
+        assert_eq!(table.first(), None);
+        assert_eq!(table.last(), None);
+        table.insert(4, "hi");
+        table.insert("string", "hi");
+        assert_eq!(table.first(), Some((4, &"hi")));
+        assert_eq!(table.last(), Some((4, &"hi")));
+        table.insert(2, "bye");
+        assert_eq!(table.first(), Some((2, &"bye")));
+        assert_eq!(table.last(), Some((4, &"hi")));
+    }
+
+    #[test]
+    fn test_table_format_debug() {
+        let mut table = Table::new();
+        assert_eq!(format!("{:?}", table), r#"()"#);
+        assert_eq!(format!("{:#?}", table), r#"()"#);
+
+        table.insert(10, "hello");
+        table.insert("twenty", "there");
+        table.insert("sp ace", "quotes");
+        assert_eq!(
+            format!("{:?}", table),
+            r#"(10="hello", "sp ace"="quotes", "twenty"="there")"#,
+        );
+        assert_eq!(format!("{:#?}", table).lines().collect::<Vec<_>>(), [
+            "(",
+            r#"    10 = "hello","#,
+            r#"    "sp ace" = "quotes","#,
+            r#"    "twenty" = "there","#,
+            ")",
+        ]);
+    }
+}