lambda , function , mapcar , apply , foreach : explained

[samifox]

why apply do this :

 

_$ (apply '+ '(1 2 3))
6

 

while mapcar do that

 

$ (mapcar '+ '(1 2 3))
(1 2 3)

[Lee Mac]

why apply do this :

 

_$ (apply '+ '(1 2 3))
6

while mapcar do that

 

$ (mapcar '+ '(1 2 3))
(1 2 3)

 

Because:

(apply '+ '(1 2 3))

Is equivalent to:

(+ 1 2 3)

Whereas:

(mapcar '+ '(1 2 3))

Is equivalent to:

((+ 1) (+ 2) (+ 3))  -->  (1 2 3)

I would suggest reading the documentation on the apply & mapcar functions; you might also find this tutorial on mapcar/lambda useful for your understanding.

[neophoible]

why apply do this :

 

_$ (apply '+ '(1 2 3))
6

while mapcar do that

 

$ (mapcar '+ '(1 2 3))
(1 2 3)

Why indeed! apply applies a function to one list, whereas mapcar is mapped to matching elements in the list(s) provided, which means they must be of equal length. There doesn't seem to be much point to the mapcar example you gave (and you might even ask why it worked at all), but mapping '- might be useful thus.