doOp v (LExternal rf) [_,len,x]
   | rf == sUN "prim__readChars"
       = v ++ "idris_readChars(vm, GETINT(" ++ creg len ++
                                "), GETPTR(" ++ creg x ++ "))"
doOp v (LExternal rf) [_,len,x]
   | rf == sUN "prim__readChars"
       = v ++ "idris_readChars(vm, GETINT(" ++ creg len ++
                                "), GETPTR(" ++ creg x ++ "))"
doOp v (LExternal rf) [_,len,x]
   | rf == sUN "prim__readChars"
       = v ++ "idris_readChars(vm, GETINT(" ++ creg len ++
                                "), GETPTR(" ++ creg x ++ "))"