1 files changed, 59 insertions, 0 deletions
diff --git a/src/func/map.rs b/src/func/map.rs
new file mode 100644
index 00000000..880fe3e6
--- /dev/null
+++ b/src/func/map.rs
@@ -0,0 +1,59 @@
+//! A deduplicating map.
+
+use std::collections::HashMap;
+use std::hash::Hash;
+
+use crate::syntax::{Spanned, ParseResult};
+
+/// A deduplicating map type useful for storing possibly redundant arguments.
+#[derive(Debug, Clone, PartialEq)]
+pub struct ConsistentMap<K, V> where K: Hash + Eq {
+    map: HashMap<K, V>,
+}
+
+impl<K, V> ConsistentMap<K, V> where K: Hash + Eq {
+    pub fn new() -> ConsistentMap<K, V> {
+        ConsistentMap { map: HashMap::new() }
+    }
+
+    /// Add a key-value pair.
+    pub fn add(&mut self, key: K, value: V) -> ParseResult<()> {
+        self.map.insert(key, value);
+        // TODO
+        Ok(())
+    }
+
+    /// Add a key-value pair if the value is not `None`.
+    pub fn add_opt(&mut self, key: K, value: Option<V>) -> ParseResult<()> {
+        Ok(if let Some(value) = value {
+            self.add(key, value)?;
+        })
+    }
+
+    /// Add a key-spanned-value pair the value is not `None`.
+    pub fn add_opt_span(&mut self, key: K, value: Option<Spanned<V>>) -> ParseResult<()> {
+        Ok(if let Some(spanned) = value {
+            self.add(key, spanned.v)?;
+        })
+    }
+
+    /// Call a function with the value if the key is present.
+    pub fn with<F>(&self, key: K, callback: F) where F: FnOnce(&V) {
+        if let Some(value) = self.map.get(&key) {
+            callback(value);
+        }
+    }
+
+    /// Create a new consistent map where keys and values are mapped to new
+    /// keys and values. Returns an error if a new key is duplicate.
+    pub fn dedup<F, K2, V2>(&self, _f: F) -> ParseResult<ConsistentMap<K2, V2>>
+    where F: FnOnce(K, V) -> ParseResult<(K2, V2)>, K2: Hash + Eq {
+        // TODO
+        Ok(ConsistentMap::new())
+    }
+
+    /// Iterate over the (key, value) pairs.
+    pub fn iter(&self) -> std::collections::hash_map::Iter<'_, K, V> {
+        self.map.iter()
+    }
+}