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author | Nadrieril | 2019-04-18 22:08:25 +0200 |
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committer | Nadrieril | 2019-04-18 22:08:25 +0200 |
commit | 486a26eb7cea0c99818fde2c3fd933f7aca40b52 (patch) | |
tree | b627edc56eb123bfc247c913aac5f881bb4a4833 /dhall_core | |
parent | 588127bf4105d8d4629304521abc3d992326a63a (diff) |
Use a context for substitution in normalization
Diffstat (limited to 'dhall_core')
-rw-r--r-- | dhall_core/src/context.rs | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/dhall_core/src/context.rs b/dhall_core/src/context.rs index b500226..91eec69 100644 --- a/dhall_core/src/context.rs +++ b/dhall_core/src/context.rs @@ -32,7 +32,13 @@ impl<K: Hash + Eq + Clone, T> Context<K, T> { /// lookup k n (insert j v c) = lookup k n c -- k /= j /// ``` pub fn lookup<'a>(&'a self, k: &K, n: usize) -> Option<&'a T> { - self.0.get(k).and_then(|v| v.get(v.len() - 1 - n)) + self.0.get(k).and_then(|v| { + if n < v.len() { + v.get(v.len() - 1 - n) + } else { + None + } + }) } pub fn map<U, F: Fn(&T) -> U>(&self, f: F) -> Context<K, U> { |