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Diffstat (limited to 'dhall/src/phase/normalize.rs')
-rw-r--r-- | dhall/src/phase/normalize.rs | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/dhall/src/phase/normalize.rs b/dhall/src/phase/normalize.rs index da19dc1..7d86833 100644 --- a/dhall/src/phase/normalize.rs +++ b/dhall/src/phase/normalize.rs @@ -372,6 +372,60 @@ enum Ret<'a> { Expr(ExprF<Thunk, X>), } +/// Performs an outer join of two HashMaps. +/// +/// # Arguments +/// +/// * `ft` - Will convert the values of the first map +/// into the target value. +/// +/// * `fu` - Will convert the values of the second map +/// into the target value. +/// +/// * `fktu` - Will convert the key and values from both maps +/// into the target type. +/// +/// # Description +/// +/// If the key is present in both maps then the final value for +/// that key is computed via the `fktu` function. Otherwise, the +/// final value will be calculated by either the `ft` or `fu` value +/// depending on which map the key is present in. +/// +/// The final map will contain all keys from the two input maps with +/// also values computed as per above. +pub(crate) fn outer_join<K, T, U, V>( + mut ft: impl FnMut(&T) -> V, + mut fu: impl FnMut(&U) -> V, + mut fktu: impl FnMut(&K, &T, &U) -> V, + map1: &HashMap<K, T>, + map2: &HashMap<K, U>, +) -> HashMap<K, V> +where + K: std::hash::Hash + Eq + Clone, +{ + let mut kvs = HashMap::new(); + + for (k1, t) in map1 { + let v = if let Some(u) = map2.get(k1) { + // The key exists in both maps + // so use all values for computation + fktu(k1, t, u) + } else { + // Key only exists in map1 + ft(t) + }; + kvs.insert(k1.clone(), v); + } + + for (k1, u) in map2 { + // Insert if key was missing in map1 + kvs.entry(k1.clone()).or_insert(fu(u)); + } + + kvs +} + pub(crate) fn merge_maps<K, V>( map1: &HashMap<K, V>, map2: &HashMap<K, V>, |