diff options
author | NanoTech | 2016-12-08 03:12:38 -0600 |
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committer | NanoTech | 2017-03-10 23:48:28 -0600 |
commit | e72192c0c1825f36f054263437029d05d717c957 (patch) | |
tree | 5002416c3e358edc3e1ca70a1aba68b97ea1e02c /src/context.rs | |
parent | 9598e4ff43a8fd4bc2aa2af75ff1094c2ef96258 (diff) |
Begin implementing type checking
Diffstat (limited to 'src/context.rs')
-rw-r--r-- | src/context.rs | 52 |
1 files changed, 52 insertions, 0 deletions
diff --git a/src/context.rs b/src/context.rs new file mode 100644 index 0000000..4d6abf2 --- /dev/null +++ b/src/context.rs @@ -0,0 +1,52 @@ +use std::borrow::Cow; +use std::collections::HashMap; + +/// A `(Context a)` associates `Text` labels with values of type `a` +/// +/// The `Context` is used for type-checking when `(a = Expr X)` +/// +/// * You create a `Context` using `empty` and `insert` +/// * You transform a `Context` using `fmap` +/// * You consume a `Context` using `lookup` and `toList` +/// +/// The difference between a `Context` and a `Map` is that a `Context` lets you +/// have multiple ordered occurrences of the same key and you can query for the +/// `n`th occurrence of a given key. +/// +#[derive(Debug, Clone)] +pub struct Context<'i, T>(HashMap<Cow<'i, str>, Vec<T>>); + +impl<'i, T> Context<'i, T> { + /// An empty context with no key-value pairs + pub fn new() -> Self { + Context(HashMap::new()) + } + + /// Look up a key by name and index + /// + /// ```c + /// lookup _ _ empty = Nothing + /// lookup k 0 (insert k v c) = Just v + /// lookup k n (insert k v c) = lookup k (n - 1) c -- 1 <= n + /// lookup k n (insert j v c) = lookup k n c -- k /= j + /// ``` + pub fn lookup<'a>(&'a self, k: &str, n: usize) -> Option<&'a T> { + self.0.get(k).and_then(|v| v.get(n)) + } + + pub fn map<U, F: Fn(&T) -> U>(&self, f: F) -> Context<'i, U> { + Context(self.0.iter().map(|(k, v)| (k.clone(), v.iter().map(&f).collect())).collect()) + } +} + +impl<'i, T: Clone> Context<'i, T> { + /// Add a key-value pair to the `Context` + pub fn insert(&self, k: Cow<'i, str>, v: T) -> Self { + let mut ctx = (*self).clone(); + { + let m = ctx.0.entry(k).or_insert(vec![]); + m.push(v); + } + ctx + } +} |