;; CSC 151 (SEMESTER)
;; Lab: Strings
;; Authors: YOUR NAMES HERE
;; Date: THE DATE HERE
;; Acknowledgements:
;;   ACKNOWLEDGEMENTS HERE

;; In this lab you will be working with your partner to discover
;; common ways we manipulate characters and strings in Scheme.
;; 
;; For this lab, the partner nearer the board will drive on the
;; exercises marked "B" and the partner further from the board
;; will drive on the exercises marked "A".

;; 1. Make sure to introduce yourself to your partner.
;;
;; 2. Make sure to discuss work habits and any questions on the reading.
;;
;; 3. Make sure to upload this file as `strings.scm`.
;;
;; 4. Optional: Review the Q&A.

;; +---------------+--------------------------------------------------
;; | Supplied code |
;; +---------------+

(define ??? "undefined")

;; +--------------------------+---------------------------------------
;; | Exercise 1: Creating @'s |
;; +--------------------------+

;; Driver: A

;; Develop three ways of constructing the string "@@@": one using a call
;; to `make-string`, one a call to `string`, and one a call to 
;; `list->string`.

(define making-@s-with-make-string ???)

(define making-@s-with-string ???)

(define making-@s-with-list->string ???)

; +---------------------------------+--------------------------------
; | Exercise 2: Textual experiments |
; +---------------------------------+

;; Driver: B

;; Each of the following expressions evaluates to a string.  For each
;; expression write (a) its length of its resulting string value and
;; (b) a sentence description of the resulting string.

(define texperiment1 "")
;; Length of texperiment1: 
;; Description of texperiment1: 

(define texperiment2 "hello world!")
;; Length of texperiment2: 
;; Description of texperiment2: 


(define texperiment3 "\"hello world!\"")
;; Length of texperiment3: 
;; Description of texperiment3: 

(define texperiment4 (string #\space))
;; Length of texperiment4: 
;; Description of texperiment4: 

(define texperiment5 (string))
;; Length of texperiment5: 
;; Description of texperiment5: 

;; Enter any notes on what you've learned from this exercise.
;;

; +------------------------+-----------------------------------------
; | Exercise 3: Substrings |
; +------------------------+

;; Driver: B

;; Consider the string "Department". Using the `substring` procedure, we
;; can extract a wide variety of words from this one string. Write a
;; Racket expression to extract each of the requested words below. You
;; may use substring multiple times in combination with string-append,
;; but please do not use string constants (e.g. "apart"), characters, or
;; any other procedures.

;; a. Write an expression to extract the string "Depart" from "Department".
;; b. Write an expression to extract the string "part" from "Department".
;; c. Write an expression to extract the string "ment" from "Department".
;; d. Write an expression to extract the string "a" from "Department".
;; e. Write an expression to extract the empty string from "Department".
;; f. Write an expression to extract the string "Dent" from
;;    "Department". Note that you may need to use two calls to `substring`
;;    along with a call to `string-append`.
;; g. Write an expression to extract the string "apartment" from
;;    "Department". Once again, you may need multiple calls.

;; Use the interactions pane to check that each of your defined
;; expressions produces the desired value.

(define substring-ex-a "TODO!")

(define substring-ex-b "TODO!")

(define substring-ex-c "TODO!")

(define substring-ex-d "TODO!")

(define substring-ex-e "TODO!")

(define substring-ex-f "TODO!")

(define substring-ex-g "TODO!")

;; +---------------------------------+--------------------------------
;; | Exercise 4: Referencing lengths |
;; +---------------------------------+

;; Driver: A

;; Here are two opposing views about the relationship between
;; `string-length` and string-ref:
;; 
;; a. "No matter what string str is, provided that it is not the empty
;;    string, `(string-ref str (string-length str))` will return the last
;;    character in the string."
;; b. "No matter what string str is,
;;    `(string-ref str (string-length str))` is an error."

;; Which, if either, of these views is correct? Why? Experiment with code
;; in the interactions pane, substituting concrete strings for str (e.g.,
;; "hello world!"), to arrive at an answer. Answer this in a sentence or
;; two in the space below.

; +---------------------------------------+--------------------------
; | Exercise 5: Building simple sentences |
; +---------------------------------------+

;; Driver: B

;; a. Consider the following definitions.

(define person "my lab partner")
(define adjective "awesome")

(define like
  (string-append 
     "I like " 
     person 
     " because " 
     person 
     " is "
     adjective
     "."))

;; What value do you expect `like` to have?

;; ENTER YOUR ANSWER HERE

;; b. Enter the expressions in Scamper's interactions pane (REPL) and check
;; your result.

;; ENTER THE VALUE OF `like` HERE

;; c. Write a procedure that does the same thing as this definition.
;; (That is, write a procedure, `like-person`, that takes a person and 
;; an adjective as inputs and produces a string that describes the person.

(define like-sentence
  ???)

;; d. Write another "template sentence" procedure of your own design. Make sure 
;; to take at least two parameters.

(define our-sentence
  ???)

; +---------------------------------+--------------------------------
; | Exercise 6: Deleting characters |
; +---------------------------------+

;; DRIVER: A

;; Write a procedure, `(delete-char str pos)`, that creates a new string 
;; by deleting the character at position `pos` from `str`.
;; 
;; For example,
;; 
;;     > (delete-char "starlings" 8)
;;     "starling"
;;     > (delete-char "starling" 4)
;;     "staring"
;;     > (delete-char "staring" 2)
;;     "string"
;;     > (delete-char "string" 2)
;;     "sting"
;;     > (delete-char "sting" 1)
;;     "sing"
;;     > (delete-char "sing" 3)
;;     "sin"
;;     > (delete-char "sin" 0)
;;     "in"
;;     > (delete-char "in" 1)
;;     "i"
;;     > (delete-char "i" 0)
;;     ""
;; 
;; Example suggested by one of the Rebelsky offspring.

(define delete-char
  (lambda (str pos)
    ???))

; +-------------+----------------------------------------------------
; | Wrapping Up |
; +-------------+

;; Congratulations on finishing this lab!  To turn in your work:
;; 
;; a. Make sure you've put your names, your section, and the date at the
;; top of the file.
;;
;; b. Save the file to disk. Make sure this file is named `strings.scm`.
;;
;; c. Submit this final file to Gradescope.  Make sure, if appropriate,
;;    to submit your work as a group submission and include your
;;    partner in the submission.

;; +---------------------------+--------------------------------------
;; | For those with extra time |
;; +---------------------------+

;; If you find that you finish all of these problems early, try one
;; or more of the following problems.  Note that some of these problems
;; require you to write procedures.

;; +-----------------------------------+------------------------------
;; | Extra 1: Collating your sequences |
;; +-----------------------------------+

;; In the reading, we discussed the fact that Scheme assigns each of its
;; characters a unique integer.  These numbers are called a "collating
;; sequence".  In this exercise, we'll explore these sequences in more
;; detail.

;; a. Compare notes with your partner about your answers to Check 2:
;; Collating sequences from the reading.  Use this acquired knowledge
;; to answer the following question:

;; What are the collating sequence numbers for the uppercase English
;; letters (A--Z)?  Write your answer in the space below:
;; (Hint: the description should be shorter than listing 26 letter-number
;; pairs!)

;; REPLACE THIS WITH YOUR ANSWER

;; b. Use your answer from part (a) to describe in a few sentences a
;; method for determining if a character is an upper-case English letter
;; by using collating sequences and subtraction.

;; REPLACE THIS WITH YOUR ANSWER

;; c. Describe how you would extend your answer to part (b) to also
;; include lower-case English letters.  Can you just use the numbers
;; corresponding to 'A' (the beginning of the uppercase letter sequence)
;; and 'z' (the end of the lowercase letter sequence) or do we need to do
;; something more complicated?

;; REPLACE THIS WITH YOUR ANSWER

;; d. Finally, let's think a little bit more broadly!  What about other
;; ;languages?  For example, below are lowercase and uppercase alpha and
;; omega, the beginning and end of the Greek alphabet:

;; Α (uppercase alpha---note: *not* A!)
;; α (lowercase alpha)
;; Ω (uppercase omega)
;; ω (lowercase omega)

;; Describe in a few sentences how you would incorporate other languages
;; into your technique.  If you have the capability, try out letters in
;; other languages to see if your technique still works!

;; REPLACE THIS WITH YOUR ANSWER