Function recognize_zip_map_where 

pub fn recognize_zip_map_where(
    stmts: &[Stmt<'_>],
    interner: &Interner,
    wanted: &dyn Fn(&ZipMap) -> bool,
) -> Result<ZipMap, ZipMapReject>

recognize_zip_map for the first loop whose zip map wanted accepts; one it turns away counts as ZipMapReject::UnsupportedTerm (its term is not the one asked for).