;=====
; Racket examples from CS 111 - Week 1 Lecture 2,
; cleaned up after class!
; last modified: 2024-08-29
; this is a comment (anything from a semicolon to the end of the line)
; * comments are IGNORED by the computer!
; * they are there for HUMANS to read
;=====
; data type: number
; can have digits smushed together,
; optionally with a single . decimal point
; optionally starting with a + or -
; these are all simple expressions of type number
27 ; I am also a comment
2
123456789.0111
+27
-27
; in BSL Racket, you can separate expressions using blanks
; as well as newlines
; below: eight simple expressions of data type number
1 2 3 4 5 -7 5555 .45
; this attempted simple expression below does NOT follow
; the syntax ruls for a number;
; UNCOMMENT the line below (REMOVE the ;) and click run
; to see the error message you get!
; 1.2.3
;=====
; data type: string
; anything written in double quotes is considered
; a simple expression literal of type string
; three simple expressions of data type string
"moo"
"Hello how are you ?"
"oh
does
this
work?"
;=====
; data type: boolean
; for BSL Racket: the two most-basic literal simple expressions
; of type boolean
; are #true and #false
; BUT!!!! it also accepts true and #t for #true (considers true and #t to
; also have the value #true)
; it also accepts false and #f for #false (consider false and #f to
; also have the value #false
; so - these are six simple expressions all of data type boolean
#true
#false
#t
#f
true
false
;=====
; data type: image
; you can paste in a copied .jpg or .png or .tiff or .svg
; image into DrRacket and that is considered a simple
; expression of type image
;=====
; I searched for "dachshund small image" in a browser,
; right-clicked on and copied the desired image in the
; browser results,
; then clicked on DrRacket's Interactions window,
; and used control/command v to paste in the image!
; (Edit menu -> Paste works, also)
; NOTE: pasting in an image changes the Racket format "under the hood"
; in the .rkt file so that the image can be represented --
; in DrRacket it looks fine,
; but if you open the .rkt file in something OTHER than DrRacket,
; the format looks decidedly strange!
;=====
; compound expressions
;
; because we want to DO things! simple expressions alone are not
; enough!
;
; in BSL Racket, here is THE syntax for compound expressions:
;
; (operation expression expression expression ...)
; ^ these expressions are called arguments
;
; operation is followed by at least one blank/newline,
; argument expressions are separated by at least one
; blank/newline
;
; semantics: what is the value of a compound expression?
; the value returned by its operation when it is executed
; using those argument expressions
;
; NOTE: the data type of a compound expression is the data type
; of the value its operation returns
; NOTE: it depends on the individual operation
; how many and
; what data types of argument expressions it expects,
; and what order they must be in
;=====
; * is a supported operator for multiplication
;
; operator * expects two or more arguments of type number
; and returns the product of it number arguments
(* 3 8
5)
; THIS IS BAD STYLE
(* 3
8
5
)
; common arithmetic operators that Racket supports!
; each expects two more more argument expressions of type number,
; returns a value of type number that is the result of applying
; that operation to those argument expressions (in the order they
; appear)
;
; * multiply
; / divide
; + add
; - subtraction
(* 3 5)
(/ 3 5)
(+ 3 5)
(- 3 5)
; BY THE WAY -- we said a compound expression expects one or more
; expressions after its operation;
; ...those can be simple expressions OR compound expressions!
(+ 6 7
(* 3 2.2)
(- 7 8))
;=====
; some operations have names -- functions!
; and some operations return a value with a data type
; other than number!
; for example!
;=====
; string-append expects two or more string arguments
; and returns ONE string of those all smushed together
(string-append "m" "ooooo" "!" " ha! ")
;=====
; operators
; < > =
; expect two or more number arguments,
; return a boolean whose value is whether the number arguments
; meet that relationship
(< 3 5)
(> 3 5)
(= 3 5)
(< (+ 3 5)
(* 3 5))
; NOTE -- = operator ONLY works with argument expressions of type number!
; * but there ARE some operations to compare expressions of other types;
; * FOR EXAMPLE:
; string=? can be used to compare string expresssions, and returns
; whether its string argument expressions have the same value
(string=? "moo"
(string-append "m" "oo"))
;=====
; and IF you add this module using the special require operation:
(require 2htdp/image)
; NOW you can use operations from this Racket module!
; NOW I have image operations!
; for example:
; the circle function expects a desired radius in pixels,
; the desired style expressed as a string: "solid" or "outline:,
; and a color (one option is to write a known color name as a string),
; and it returns an image depicting a circle image with that radius,
; style, and color!
(circle 30 "solid" "cyan")
; uncomment to see the error you get if you try to call it with
; a "bad" color argument expression:
;(circle 30 "solid" "moo")
; for example:
; the above function expects one or more images
; and returns a single image that is a vertical "stack"
; of the image argument expressions
(above (circle 30 "solid" "cyan")
(rectangle 100 30 "outline" "purple"))
;=====
; You can read about more of the operations/functions in
; the module 2htdp/image in the DrRacket documentation --
; * go to the DrRacket Help menu,
; * select "Racket Documentation" near the top,
; * enter in 2htdp/image in the ...search manuals... textfield
; in the top-left corner
; ...and select the link to the 2htdp/image module's documentation
; that results --
; ...scroll through the index on the left-hand-side, it has links to
; descriptions of the many functions in the 2htdp/image module!