[obsidian] vault backup: 2023-09-01 18:50:32[
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@ -20,14 +20,28 @@ fn eval<'a>(expr:Expr,env:&'a mut Vec<(String,Val)>)->Result<Val,Error>{
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Environmentは評価全体で見ればLetやLambdaごとに分岐していく構造だけれど、局所的には1列のベクタで表現できる
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こんな感じすかねえ
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```rust
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struct<'a,T> Environment(&'a mut Vec<T>)
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impl<'a,T> Environment{
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pub fn new()->Self{
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Self(&mut Vec::new())
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}
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struct EnvironmentT<'a, T>(&'a mut Vec<(String, T)>, usize);
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impl<'a, T> EnvironmentT<'a, T> {
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pub fn new(vec: &'a mut Vec<(String, T)>, mut names: Vec<(String, T)>) -> Self {
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let len = vec.len();
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vec.append(&mut names);
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Self(vec, len)
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}
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pub fn drop(&mut self) {
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self.0.truncate(self.1);
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}
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pub fn lookup(&self, name: &String) -> Option<&'a T> {
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let res = self
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.0
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.iter()
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.rev()
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.filter(|(n, _v)| name == n)
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.collect::<Vec<_>>();
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res.get(0).map(|(_, v)| v)
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}
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}
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```
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