Macro pear::pear_try

macro_rules! pear_try {
    ([$name : ident ; $input : ident] $e : expr) => { ... };
    ([$name : ident ; $input : ident] $e : expr => $r : expr) => { ... };
    ([$name : ident ; $input : ident] $pat : ident @ $e : expr => $r : expr) => { ... };
}

FIXME: This is an issue with rustc here where if $input is expr everything fails.