Scheme is a minimalist dialect of the Lisp family consisting of a small core for language extension.
Scheme follows the “Prefix Notation”, where operations use the format (* 5 5) instead of (5 * 5). For example, if we wanted to add a lot of numbers together, we conventionally do 2 + 3 + 4 + 6 + 11, in Scheme we would instead write (+ 2 3 4 6 11), which is much more concise.
Arithmetic
A pair of parentheses indicates one step of calculation. A function name comes after the open parenthesis followed by arguments. Tokens are reparated by spaces, tabs and newlines.
(/ (* (+ 2 3) (- 5 3)) 2)
Other included arithmetic operators are:
| quotient | sin | exp | asin |
| remainder | cos | log | acos |
| modulo | tan | sqrt | atan |
Variables
To define a variable, use define, to print the value of an expression, use display.
(define color "red") (display color)
Functions
To define a function, use define, to add parameters to the function, use lambda. The following functions can thereafter be used like (greet "Alex").
(define greet (lambda (name) (string-append "Hello " name "!")))
Another example:
(define add-three (lambda (a b c) (+ a b c)))
The previous example can also be defined using the following short-form:
(define (add-three a b c) (+ a b c))
List
You can create a list of items, and access items in the list by id:
(define colors (list red yellow green cyan)) (list-ref colors 2) ; yellow
Logic
Logic operations are in the format of (if true this that) where the result of the operation will be this if the second parameter is true, otherwise will be that. In Scheme, true is indicated as #t, and falseis indicated as #f.
(define (min a b) (if (< a b) a b))
Compare
eq? | Compares addresses of two objects and returns #t if they are same. |
|---|---|
eqv? | Compares types and values of two object stored in the memory space and returns #t if they are same. |
equal? | Compares sequences such as list or string and returns #t if they are same. |