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diff --git a/Douglas_Richardson.md b/Douglas_Richardson.md new file mode 100644 index 0000000..af86b16 --- /dev/null +++ b/Douglas_Richardson.md @@ -0,0 +1,144 @@ +# Hermes project report + +## Douglas Richardson +### April 28, 2017 + +# Overview +Hermes is a multi-user chat program that allows users to setup a server, connect to it +and communicate with all other members of the server. + +Hermes uses TCP pipes to tread input and output like a port. Essentially, each client sends +information to the server and depending on the input, the server decides what to do with it +and usually sends output back to all the other users. + +# Libraries Used +The code uses two non-default libraries: + +``` +(require racket/gui/base) +(require math/base) +``` + +* The ```racket/gui/base``` library is the primary library for the GUI. +* the ```math/base``` is used for random number generation. + +# Key Code Excerpts + +Here is a discussion of the most essential procedures, including a description of how they embody ideas from +UMass Lowell's COMP.3010 Organization of Programming languages course. + +Five examples are shown and they are individually numbered. + +## 1. Initializing the gui + +This line of code allows us to wrap the gui into an object. + +``` +(define (make-gui) + ... + (cond ((eq? command 'show) (lambda () (send main-frame show #t))) + ((eq? command 'get-color) get-my-color) + ((eq? command 'set-color) set-color) + ((eq? command 'prompt-color) prompt-color) + ((eq? command 'prompt-username) prompt-username) + ((eq? command 'prompt-hostname) prompt-hostname) + ((eq? command 'send) send-message) ;; call to show a message in a gui + ((eq? command 'set-name) (lambda (newname) (if (string? newname) + (set! name newname) + (print "Thats not good")))) + ; ((eq? command 'recieve-message) user-message) + ; ((eq? command 'get-list) listy) + ; ((eq? command 'set-list) update) + ;;Something up with that + ; else should assume a message and output to screen we do not want it + ; to fail + ((eq? command 'get-message) get-message) + (else (error "Invalid Request" command)) + )) + ;;dispatch goes below that + dispatch)``` + +This allows us to make our code simpler and lets us treat the gui like an object in it's self. +Giving the gui commands to change it's self rather than having to remember all the commands it has. + +## 2. Working with lists + +This code is code that allows us to append a new message onto the end of the list of messages using recursion + +``` +(define (appendlist listoflist add-to-end) + (if (null? listoflist) + (cons add-to-end '()) + (cons (car listoflist) (appendlist (cdr listoflist) add-to-end))))``` + +Normally there is a function to just append onto the end of a list, however the problem is that if we attempt to append +a list of elements onto the end of a list, it just appends the elements onto the end of the list. For example if I had +a list of the following '(("Doug" "Hello World!" "Purple")) +and wanted to append the list '("Gordon" "No one else is here Doug." "Black") The list I want back would be +'(("Doug" "Hello World!" "Purple")("Gordon" "No one else is here Doug." "Black")) but if I use the default +list append I get'(("Doug" "Hello World!" "Purple")"Gordon" "No one else is here Doug." "Black") +which is no good for the gui. + +This follows on our idea of working with lists and using recursion to walk down a list. + +## 3. Re-drawing messages + +The following procedure is used to re-draw messages onto the canvas after a screen move or resize. + +``` + (define (update-helper given-list) + (if (null? given-list) + '() + (if (null? (car given-list)) + '() + (begin (user-message + (get-username-from-list (car given-list)) + (get-message-from-list (car given-list)) + (get-color-from-list (car given-list))) + (update-helper (cdr given-list))))))``` + +While it doesn't actually use the map function, this is a map as for every element of a list (each element is a list of three strings) +it runs a procedure (or in this case a set of procedures) in the order of the list. + +## 4. Parsing Messages + +This line of code is used to parse a single string message into a three string message + +``` + (define (user-message-parse string-i start) + (define (helper str index) + (if (eq? (string-ref str (+ start index)) #\~) ; regexes would allow us + ; to avoid this #\~ + (substring str start (+ start index)) + (helper str (+ index 1)))) + (helper string-i 0))``` + +This was used to parse a string into smaller strings. In hermes we can only send one string to each client at one time, therefore +the three elements that the gui uses to print messages need to be compressed together. We append a ~ inbetween each of these so we can +parse them out at the client end. + +While we don't run any commands off it (saved that part for the commands we do interpret from strings) +it is similar to the symbolic differentaitor. + +## 5. Color setting + Here we have an example of when we use a symbolic differentiator in the gui to determine when a user wants to run a command + rather than input text. + + ``` + (define (button-do-stuff b e);b and e do nothing :/ + (if (color-change-request? (send input get-value)) + (set! my-color (get-color-from-input (send input get-value))) +... + + (define (color-change-request? given-string) + (if (> (string-length given-string) 7) + (if (equal? (substring given-string 0 6) "/color") + #t + #f) + #f))``` + +The procedure button-do-stuff is run every time the user presses the return key or presses the send button on the gui +and what it will do is check to see if the user typed in "/color", and if they did it sets the internal color to be +what the user said after that. This is part of our symbolic differentiator that allows the user to use commands +rather than the typical use of the input (which is just to send a message to other clients) + |