Difference between apply and funcall

Question

(describe-function apply) says:

apply is a built-in function in ‘src/eval.c’.                                                                                                                                                                      

(apply FUNCTION &rest ARGUMENTS)                                                                                                                                                                                   

Call FUNCTION with our remaining args, using our last arg as list of 
args.                                                                                                                                         
Then return the value FUNCTION returns.                                                                                                                                                                            
Thus, (apply '+ 1 2 '(3 4)) returns 10.  

(describe-function funcall) says:

funcall is a built-in function in ‘src/eval.c’.                                                                                                                                                                    

(funcall FUNCTION &rest ARGUMENTS)     

Call first argument as a function, passing remaining arguments to it.
Return the value that function returns.
Thus, (funcall 'cons 'x 'y) returns (x . y).

What is the difference between these two function?

Answer 1

Use apply when you don't know what the individual arguments are, or how many there are. You can use funcall (or apply) when you do know that.

For example, suppose your list of args to apply the function to is the value of variable foo. Then you would use (apply 'some-fun foo).

If you know that you're going to apply the function to args 3, toto, and 4, in that order, then you can use (apply 'some-fun (list 3 'toto 4)) or (funcall 'some-fun 3 'toto 4).