how to write a elisp function like this

I'm trying to write a elisp function like this: (setq lst '(("abc" . "c") ("cde" . "f"))) (foo "a" lst) ;=>"c" (foo "b" lst) ;=>"c" (foo "c" lst) ;=>"c" (foo "d" lst) ;=>"f" I know if the first string is same as the key string I can use assoc. (setq lst '(("a" . "c") ("d" . "f"))) (cdr (assoc "a" lst)) ;= "c" (cdr (assoc "d" lst)) ;= "f" I could enable the function by writing the lst separately, but I don't think it's the best way to do. (setq lst '(("a" . "c") ("b" . "c") ("c" . "c") ("c" . "f") ("d" . "f") ("f" . "f") )) Can someone help me how to write the function like foo?