>Do not use \ at end of line inside {}, because \ is an operator in >GP , so a \ b is legal. Instead indent your code
I admit that this use of "\" is not pretty, but I happen to use copy-paste a lot from my source files to the PARI_GP interpreter and the indented code you suggest will not compile correctly if copy-pasted into the interpreter, it will interpret every line break as a separator between different functions or instructions.