; stuff - anything from a semicolon to the
;    end of a line is a Racket COMMENT, and will
;    be ignored!

;=====
; expression: a "chunk" that has meaning in
;    a programming language

;=====
; simple expression: the simplest form of
;     expression

; what you can DO with an expression
;    is based on its DATA TYPE

; the syntax of a simple expression
;    determines its data type

;=====
; for data type number, I must follow
;     Racket's syntax rules for its
;     number type -- 1 or more digits,
;     possibly started with a -,
;     possibly containing ONE decimal point:

4
10000
42

42.20
000003
.00003

-34
-3.4

; data type string: anything in double-quotes
;    is considered a simple expression of
;    type string

"moo"
"duck"
"Zeke"

"-34"

;=====
; Boolean type: #true #false

#true
#false

;=====
; and image is supported as a simple
;    expression type in Racket

; if you copy an image DrRacket, it is considered
;    a simple expression of type image



;=====
; compound expressions!

; in Beginning Student Language (BSL)
;    Racket, a compound expression has
;    THIS syntax:

; (operation argument-expression1
;            argument-expression2
;            ...
;            )
;
; *   the argument expressions following
;     the operation are separated by blanks
;     or newlines (not commas!)
;
; *   the data type of a compound expression
;     is the data type of the value its operation
;     computes, of the value its operation
;     RETURNS
;
; *   how many argument expressions you can have
;     depends on the operation -- each operation
;     expects a particular number and type
;     of argument expressions

;=====
; SO -- what kind of operations are available in Racket?
;
; *   has some built-in operators
; *   has some built-in functions
; *   has some available modules, collections or
;     libraries of additional operators and functions
; *   AND... you can write your OWN operations, your own
;     functions!  <-- starting next week!
;
; here are a FEW of the built-in operations...

;=====
; arithmetic operators!
; *   such as:   +  -  *  /
;
; *   these expect two or more argument expressions,
;     each of type number,
;     and return a number that is the result of
;     performing that arithmetic operator on
;     those argument expressions

(+ 4 3 7 42 20 17 10000 500 1 19)
(- 4 3)
(* 4 3)
(/ 4 3)

;=====
; some operations return types other than number,
; and some operations have names -- these are FUNCTIONS!

;=====
; string-append expects two or more argument
;     expressions of type string, and returns
;     a single string expression consisting
;     of the values of its arguments appended
;     (smushed) together

(string-append "me" "ow")

;=====
; operator = expects two or more arguments of type
;     number, and returns whether all of
;     its arguments have the same value

(= (- 4 3) 1)

;=====
; the require funcction is special --
;    it expects the name of a Racket module,
;    a collection of Racket definitions,
;    and it returns NOTHING (!!), 
;    BUT has the SIDE-EFFECT of making
;    those definitions available for use in
;    the rest of this Definitions
;    window/in expressions in the rest of
;    this .rkt file!

; 2htdp/image is the image library provided
;    by the "How to Design Programs", 2nd edition
;    text!

(require 2htdp/image)

;=====
; one operation 2htdp/image provides is a
;     star function --
;     it expects the desired distance between
;     a 5-pointed star's points in pixels,
;     a style string "solid" or "outline",
;     and a color, and it returns an image
;     of a star of that size, style, and color!

(star 30 "solid" "purple")