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#![feature(proc_macro_quote)]
extern crate proc_macro;
use proc_macro::*;
#[proc_macro]
pub fn cond(input: TokenStream) -> TokenStream {
let mut conds = Vec::new();
let mut input = input.into_iter().peekable();
while let Some(tree) = input.next() {
let cond = match tree {
TokenTree::Group(tt) => tt.stream(),
_ => panic!("Invalid input"),
};
let mut cond_trees = cond.clone().into_iter();
let test = cond_trees.next().expect("Unexpected empty condition in `cond!`");
let rhs = cond_trees.collect::<TokenStream>();
if rhs.is_empty() {
panic!("Invalid macro usage in cond: {}", cond);
}
let is_else = match test {
TokenTree::Ident(ref word) => &*word.to_string() == "else",
_ => false,
};
conds.push(if is_else || input.peek().is_none() {
quote!({ $rhs })
} else {
quote!(if $test { $rhs } else)
});
}
conds.into_iter().flat_map(|x| x.into_iter()).collect()
}
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