The AutoLisp Intermediate Tutorial

The AutoLisp Intermediate Tutorial

List Functions :

car cdr cadr caddr caar cddr foreach list cons nth

Example Programs

You are about to unravel the mystery behind the car of a cdr. Better sit down.

car - This function returns the first item of a list. The item can be a list as shown in example 3 below.

Syntax : (car list)

list - Any valid list.

(car (1 2 3)) returns 1

(car ("ab" "cde" "Jeff")) returns "ab"

(car ((1 2 3) (4 5 6))) returns (1 2 3)

(car 1) returns "Error: Bad Argument Type" [1 is an integer, not a list]

(car "Jeff") returns "Error: Bad Argument Type" ["Jeff" is a string, not a list]

(car (1 (2 3))) returns 1

(car ((1 2) 3)) returns (1 2)

This function is mainly used to get the x coordinate of a point. [ (car (x y z)) returns x ]

cdr - This function returns a list that includes everything but the first item in a list. The item can be a list as shown in example 3 below.

Syntax : (cdr list)

list - Any valid list.

(cdr (1 2 3)) returns ( 2 3)

(cdr ("ab" "cde" "Jeff")) returns ("cde" "Jeff")

(cdr ((1 2 3) (4 5 6))) returns (4 5 6) since (4 5 6) is the second item in the list.

(cdr 1) returns "Error: Bad Argument Type" [1 is an integer, not a list]

(cdr "Jeff") returns "Error: Bad Argument Type" ["Jeff" is a string, not a list]

(cdr (1 (2 3))) returns (2 3)

(cdr ((1 2) 3)) returns 3

Mystery HINT: (car (cdr ( 1 (2 3) ) ) ) returns 2 [So, that's what a car of a cdr is]

if the cdr of (1 (2 3)) returns (2 3) and the car of (2 3) returns 2 then the mystery is solved.

The car of a cdr is the first item in the second item in the list.

cadr - This function returns the second item in a list. The item can be a list as shown in example 3 below.

Syntax : (cadr list)

list - Any valid list.

(cadr (1 2 3)) returns 2

(cadr ("ab" "cde" "Jeff")) returns "cde"

(cadr ((1 2 3) (4 5 6) (7 8 9))) returns (4 5 6)

(cadr 1) returns "Error: Bad Argument Type" [1 is an integer, not a list]

(cadr "Jeff") returns "Error: Bad Argument Type" ["Jeff" is a string, not a list]

(cadr (1 (2 3))) returns (2 3)

(cadr ((1 2) 3)) returns 3

(cadr (1)) returns nil [There isn't a second item]

This function is mainly used to get the y coordinate of a point. [ (cadr (x y z)) returns y ]

caddr - This function returns the third item in a list. The item can be a list as shown in example 3 below.

Syntax : (caddr list)

list - Any valid list.

(caddr (1 2 3)) returns 3

(caddr ("ab" "cde" "Jeff")) returns "Jeff"

(caddr ((1 2 3) (4 5 6) (7 8 9))) returns (7 8 9)

(caddr 1) returns "Error: Bad Argument Type" [1 is an integer, not a list]

(caddr "Jeff") returns "Error: Bad Argument Type" ["Jeff" is a string, not a list]

(caddr (1 (2 3))) returns nil [There isn't a third item]

(caddr ((1 2) 3 (5 6) 7)) returns (5 6)

(caddr (1)) returns nil [There isn't a third item]

This function is mainly used to get the z coordinate of a point. [ (caddr (x y z)) returns z ]

caar - This function returns the first item of the first item in a list. The item can be a list as shown in example 3 below.

Syntax : (caar list)

list - Any valid list.

(caar (1 2 3)) returns "Error: Bad Argument Type" [The first item in the list is not a list]

(caar ((1 2 3)(4 5 6)) returns 1

(caar (("ab" "cde") ("Jeff")) returns "ab"

(caar (("Jeff" 1 2 3)("x" "y" "z")(4 5 6))) returns "Jeff"

(caar 1) returns "Error: Bad Argument Type" [1 is an integer, not a list]

(caar "Jeff") returns "Error: Bad Argument Type" ["Jeff" is a string, not a list]

(caar (1 (2 3))) returns "Error: Bad Argument Type" [The first item in the list is not a list]

(caar ((1 2) 3)) returns 1

cddr - This function returns a list that includes everything after the second item in a list.

Syntax : (cddr list)

list - Any valid list.

(cddr (1 2 3)) returns (3)

(cddr ("ab" "cde" "Jeff" "Sanders")) returns ("Jeff" "Sanders")

(cddr ((1 2 3) (4 5 6) (7 8 9)(10 11 12))) returns ((7 8 9)(10 11 12))

(cddr 1) returns "Error: Bad Argument Type" [1 is an integer, not a list]

(cddr "Jeff") returns "Error: Bad Argument Type" ["Jeff" is a string, not a list]

(cddr (1 (2 3))) returns nil [There isn't a third item]

(cddr ((1 2) 3 (5 6) 7)) returns ((5 6) 7)

(cddr (1)) returns nil [There isn't a third item]

foreach - This function steps through each item in the list and returns the last value.

Syntax : (foreach varName list yourFunctions)

varName - Any valid variable name that you make up.

list - Any valid list.

yourFunctions - Any valid autolisp functions.

(foreach a (list 1 2 3)(princ a)) prints 123 to the screen and returns 3 [same as (princ 1) (princ 2) (princ 3) except that it only returns the last value.]

(foreach a (list 1 2 3)(princ (+ a 5))) prints 678 to the screen and returns 8 [same as (princ (+ 1 5)) (princ (+ 2 5)) (princ (+ 3 5)) except that it only returns the last value.]

list - This function creates a list.

Syntax : (list Item)

Syntax : (list firstItem secondItem)

Syntax : (list firstItem secondItem thirdItem...)

Item - Any valid item including a list.

(list) returns nil [an Empty list]

(list 1 2 3) returns (1 2 3)

(list "ab" "cde" "Jeff" "Sanders") returns ("ab" "cde" "Jeff" "Sanders")

(list (list 1 2 3) (list 4 5 6)) returns ((1 2 3) (4 5 6))

(list 1) returns (1)

(list "Jeff") returns ("Jeff")

(list 1 (list 2 3)) returns (1 (2 3))

(list (list 1 2) 3 (list 5 6) 7) returns ( (1 2) 3 (5 6) 7)

cons - This function takes an item and a list, and returns the addition of that item to the beginning of the list. The first item can be an atom or a list.

Syntax : (cons Item list) ;thanks tim!

Item - Any valid item including a list.

list - Any valid list.

(cons) returns "Error: Too Few Arguments" [cons requires an item and a list]

(cons 1 2 3) returns "Error: Too Many Arguments" [cons requires an item and a list]

(cons "ab" (list "cde" "Jeff" "Sanders")) returns ("ab" "cde" "Jeff" "Sanders")

(cons (list 1 2 3) (list 4 5 6)) returns ((1 2 3) 4 5 6)

(cons 1) returns "Error: Too Few Arguments" [cons requires an item and a list]

(cons "Jeff") returns "Error: Too Few Arguments" [cons requires an item and a list]

(cons 1 (list 2 3)) returns (1 2 3) [notice the difference here from the list function above]

(cons "Jeff" (list 1 2 3 5 6 7)) returns ( "Jeff" 1 2 3 5 6 7 )

nth - This function returns the Nth item in a list. The first item in a list is item zero.

Syntax : (nth integer list)

integer - Any valid integer.

list - Any valid list.

(nth) returns "Error: Too Few Arguments" [cons requires an item and a list]

(nth 2 1 2 3) returns "Error: Bad Argument Type" [nth requires an integer and a list]

(nth 2 (list "cde" "Jeff" "Sanders")) returns "Sanders"

(nth 0 (list 1 2 3)) returns 1

(nth 1 (list 1 2 3)) returns 2

(nth 2 (list 1 2 3)) returns 3

(nth 1 (list "a" (list "b" "c") "d")) returns ("b" "c")

(nth 4 (list 1 2 3 5 6 7)) returns 6

Example Program 1:

(defun C:myProg() [define program]

(setq pt1(getpoint "\n First Corner: ")) [get first point]

(setq pt2(getcorner pt1 "\n Last Corner: ")) [get other point on a square]

(setq x1(car pt1)) [get x coordinate of pt1]

(setq x2(car pt2)) [get x coordinate of pt2]

(setq y1(cadr pt1)) [get y coordinate of pt2]

(setq y2(cadr pt2)) [get y coordinate of pt2]

(setq hor1(- x2 x1)) [get horizontal distance]

(setq ver1(- y2 y1)) [get vertical distance]

(princ "\n Horizontal Distance = ")(princ hor1) [print to screen]

(princ "\n Vertical Distance = ")(princ ver1) [print to screen]

(princ) [supress echo..clean exit]

) [close program]

Execution:

Command: (load "myProg")<enter>

Command: myProg<enter>

Command: First Corner: <pick a point>

Command: Last Corner: <pick a point>

Command: Horizontal Distance = 23.5

Command: Vertical Distance = 11.5

Example Program 2:

(defun C:AddText() [define program]

(setq myList(list "e" "b" "c" "m" "at")) [make a list of 6 letters]

(foreach myVar myList [start the foreach loop]

(princ (strcat myVar (nth 4 myList))) [define a valid function]

) [close the foreach statement]

(princ) [supress echo..clean exit]

) [close program]

Execution:

Command: (load "AddText")<enter>

Command: AddText<enter>

Command: eat

Command: bat

Command: cat

Command: mat

Command: atat

End of List Functions

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Last Updated January 4th, 2012