23 lines
565 B
Rust
23 lines
565 B
Rust
extern mod std;
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use std::list::*;
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pure fn pure_length_go<T: Copy>(ls: @List<T>, acc: uint) -> uint {
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match *ls { Nil => { acc } Cons(_, tl) => { pure_length_go(tl, acc + 1u) } }
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}
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pure fn pure_length<T: Copy>(ls: @List<T>) -> uint { pure_length_go(ls, 0u) }
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pure fn nonempty_list<T: Copy>(ls: @List<T>) -> bool { pure_length(ls) > 0u }
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fn safe_head<T: Copy>(ls: @List<T>) -> T {
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assert is_not_empty(ls);
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return head(ls);
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}
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fn main() {
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let mylist = @Cons(@1u, @Nil);
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assert (nonempty_list(mylist));
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assert (*safe_head(mylist) == 1u);
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}
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