;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname lect17-cond-semantics-stepper) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
(require "student-extras.rkt")

; - review: using local variables (or not)
; - syntax/semantics of `cond`, w/o '...'
; - stepping through my-max (w/ and w/o `let`)


;; We re-write the following to use 0,1,2 or 3 local variables, via `let*`:

; downcased-initial : string -> string
; Given a *non-empty* string `w`,
; return its first character, downcased.
;
#;(define (downcased-initial w)
  (string (char-downcase (string-ref w 0)))) 


;; Step through this:
(downcased-initial "hello")


#| Syntax,semantics of `cond`:

 A <cond-expr> is:
     (cond <qas>)

 A <qas> ("question/answers") is either:
   - ε                          (that's our notation for 'nothing at all')
   - [<expr_q> <expr_a>]
     <qas>


Semantics of `cond`:
  eval of (cond <qas>) returns:
    - if <qas> is ε, then: semantics say trigger a run-time error.
    - if <qas> is   [<expr_q> <expr_a>] <qas>, then:
        eval <expr_q>;
          If true:  return result of eval'ing <expr_a>.
          If false: return result of eval'ing (cond <qas>).

|#




;;;;;;;;;;;;;;; my-max



; my-max : list-of-number -> number 
;
(define (my-max a-lon)
  (cond [(empty? a-lon) -inf.0]
        [(cons? a-lon)  (if (< (first a-lon)
                               (my-max (rest a-lon)))
                            (my-max (rest a-lon))
                            (first a-lon))]))


(my-max (cons 1 (cons 2 empty)))