With this Lisp dialect, a keyword must be placed at the first position of (most) of the expressions in Lisp. In some situations (such as boolean or arithmetic operations), a keyword must not take the first position in a list.
(defun main () (
(princ "Hello World.")
; ^^^^^ <- This is the keyword.
))Currently, there are multiple keywords available with this Lisp dialect.
var
This keyword is used to declare a new variable.
setf
This keyword is used to change the value of any variable.
princ
This keyword is used to output anything in the terminal.
princln
This keyword is used to output anything in the terminal and adds a line break afterwards.
scan
This keyword is used to scan an input from the user.
if
This keyword indicates an if-statement.
while
This keyword indicates a while-loop.
defun
This keyword is used to define a new function.
return
This keyword is used to exit a function and return a value.
import
This keyword is used to import source code from another file.
The keyword var is used to declare a new variable.
IMPORTANT: Variables in Lisp do not have any datatype, so that you can store numbers, booleans, strings, etc. in them.
variable name
Represents the name of the declared variable. The variables name can be any word, as long as it does not represent any keyword, parenthesis, number, etc.
variable value (optional)
Represents the value of the declared variable. If no value is given, the variable will be initialized with a value of "0.00".
(defun main () (
;Declare a new variable with no specified value:
(var myVarWithoutValue)
;Declare a new variable with the value of 5:
(var myVarWithValue 5)
))The keyword setf is used to change a variable's value.
variable name
Represents the name of the variable, whose value should be changed.
variable value
Represents the new value, to which the variable should be changed to.
(defun main () (
(var myVar) ;Declare a new variable.
(setf myVar 15) ;Change variable's value to 15.
(setf myVar "Hello World") ;Change variable's value to "Hello World"
(setf myVar sqrt(25)) ;Change variable's value to the return value of the "sqrt(25)"-function
(setf myVar (+ 7 13)) ;Change variable's value to the result of the arithmetic operation 7 + 13.
))The keywords princ and princln are used to output anything to the terminal. princ simply prints any element into the console, while princln does the same and adds a line break afterwards.
IMPORTANT: princ and princln are capable of processing escape sequences, such as \n, \t, etc. A list with available escape sequences can be found here.
output
This element is printed into the terminal.
(defun main () (
(princ "Hello World") ;Print the String "Hello World".
(princ 15) ;Print the value 15.
(princ (* 2 14)) ;Print the result of the arithmetic operation 2 * 17.
(princ sqrt(9)) ;Print the return value of the "sqrt(9)"-function.
;Princln simply adds a line break afterwards:
(princln "Hello World") ;Print the String "Hello World".
(princln 15) ;Print the value 15.
(princln (* 2 14)) ;Print the result of the arithmetic operation 2 * 17.
(princln sqrt(9)) ;Print the return value of the "sqrt(9)"-function.
))The keyword scan is used for input actions. With this, the user can input anything. The scanned user's input is then stored into a variable.
After this keyword is encountered in the source code by the Interpreter, the user's input is scanned until the ENTER-button is pressed.
variable name
Represents the variable, in which the user's input should be stored.
(defun main () (
(var userInput) ;Declare a new variable, which is supposed to store the user's input.
(scan userInput) ;Scan the user's input and store the result in the userInput-variable.
))The keyword if indicates an if-statement. Such an if-statement executes the expressions in it's body, if the condition is considered to be true. Further information on conditions and boolean operations can be found here.
If statements can be encapsulated.
condition
This list contains a boolean comparison, which represents the condition of the statement.
body
This list contains all the expressions that are executed, if the condition is true.
else (optional)
This list contains all the expressions that are executed, if the condition is false.
(defun main () (
;If-statement without optional else-branch:
(if (= 5 5) (
; ^^^^^^^ <- This represents the condition of the statment.
(princ "5 is equal to 5.") ;Expression is executed if condition is true.
))
;If statement with optional else-branch:
(if (> 3 5) (
(princ "3 is greater than 5.") ;Expression is executed if condition is true.
) (
(princ "3 is not greater than 5.") ;Expression is executed if condition is false.
))
))The keyword while indicates an while-loop. Such a while-loop checks wether the condition is true, and executes all the expressions in it's body. This cycle is repeated, until the condition is no longer true.
condition
This list contains a boolean comparison, which represents the condition of the loop.
body
This list contains all the expressions that are executed for as long as the condition is true.
(defun main () (
(var I 0)
(while (< i 15) (
; ^^^^^^^^ <- This represents the condition.
;These expressions are executed, for as long as the value of "i" is less than 15:
(princ "iteration: ")
(princ i)
(setf i (+ i 1))
))
))The keyword defun is used to define a new function.
Further informaion on functions can be found here.
function name
This represents the function's name.
function parameters
This list contains all the parameters of the function.
function body
This list contains all the expressions, that are executed whenever the function is called.
;main-function represents the starting point of the program:
(defun main () (
(printSum(5 9)) ;Executes the "printSum()"-function.
))
;The "printSum()"-function exhibits the two parameters "a" and "b" and prints their sum:
(defun printSum (a b) (
;Expressions are executed whenever this function is called:
(princ (+ a b))
))The keyword return is used to exit a function. This keyword can be used as well to return any value from the currently executed function.
return value (optional)
This element is returned by the function.
(defun main () (
(princ mul(2 7)) ;Prints the return value of the "mul()"-function.
))
(defun mul (a b) (
(returns (* a b)) ;Returns the result of the arithmetic operation a * b.
))The keyword import is used to import source code from another file. The functions etc. of the other file can be used in the current file as well.
IMPORTANT: Please make sure that you do not create a StackOverflow when using the import statement.
file name
This element represents the file name, which should be imported.
;File: code.lsp
(defun mul (a b) (
(return (* a b))
));File: main.lsp
(import "code.lsp")
(defun main () (
(princ mul(2 5)) ;Calls the "mul()"-function from the other file.
))