Ok, here is the exact assignment.  Tiny Scheme Details: The Scheme or LISP that you are going to implement should include the following primitives: T, NIL, CAR, CDR, CONS, ATOM, EQ, NULL, INT, PLUS, MINUS, TIMES, LESS, GREATER COND, QUOTE, DEFINE. T and NIL represent true and false. In general atoms may be identifiers or integers. An identifier will start with a letter of the alphabet, and maybe followed by one or more letters or digits; only uppercase letters will be used. No underscores or other characters are allowed in identifiers. Integers may be signed or unsigned, i.e., 25, +25, −25 are all legal.   CAR, CDR, CONS are the standard Scheme primitive functions. ATOM returns T if its argument is atomic, and returns NIL otherwise. INT returns T if its argument is an atom that is a number. EQ works only on atomic arguments; it returns T if its two atomic arguments are the same [or equal, for numbers] and NIL otherwise. NULL returns T if its argument is NIL and NIL otherwise (non-atomic arguments should be acceptable to NULL). PLUS, MINUS etc., take two numbers [integers] as their arguments and return the result [an integer]. LESS and GREATER allow you to compare two integers and return T if the first is less or greater than the second respectively.   COND and QUOTE are the standard Scheme forms. DEFINE allows the user to define a new function and use it later. A function definition looks like (define (f x) fb )   where f is the function being defined; its formal parameter(s) is named x; and its body is the Scheme expression fb. When this is “evaluated”, it should add a pair (f . ((X Y) . fb)) to the d-list [the list of definitions that your interpreter should maintain internally; actually, how you store function definitions on the d-list is up to you; the above is only one possibility]. The features of Tiny Scheme that have not been included are: LAMBDA, LABEL. These are not needed because Define is sufficient for defining new functions. I thought it would be easier to post it all instead of trying to explain it. <div class="gmail_quote">On 9 November 2010 15:37, John Clements <<a href="mailto:clements@brinckerhoff.org">clements@brinckerhoff.org</a>> wrote: <blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div class="im"> On Nov 9, 2010, at 12:32 PM, Peter Breitsprecher wrote: > Ok, here is the code I have written so far for the function I am having trouble with... > > (define (rep-loop) >   (newline) >   (display "repl>") >   (read-token)) </div>I'm going to ignore rep-loop. <div class="im"> > > (define (read-token) >   (let ((expr (read-char))) >     ((cond [(char-whitespace? expr) (read-token1)] >            [(eq? expr #\() (read-token2)] >            [(eq? expr #\)) (read-token3)] >            [(char-alphabetic? expr) (read-token4)] >            [(char-numeric? expr) (read-token5)] >            [else (display "Exiting Loop")])))) </div>Okay! we've got a name: read-token. The way it's written, it's going to be very hard to test.  This is because it operates on typed-in input. This program would be much easier to develop if you could write a function that accepts strings as input.  Can we break the problem up this way? John Clements <div><div></div><div class="h5"> > The cond calls other functions I have written just so I could see it if was reading the output letter by letter...  Now I need to make read-token read the whole word if it sees a character and the entire number if it sees a number. > > Is that getting closer? > > On 9 November 2010 15:28, John Clements <<a href="mailto:clements@brinckerhoff.org">clements@brinckerhoff.org</a>> wrote: > > On Nov 9, 2010, at 12:27 PM, Peter Breitsprecher wrote: > > > I'd lie but no.. I was just trying to clarify what I was looking for.  I gave a the code for one of the functions I had written, and then an example of the input the user is giving below, and then tried to describe in more detail what I needed help with... > > Well, I'm glad you're not lying :). > > Can you start by picking a name for the function that you're trying to write? > > John Clements > > > > On 9 November 2010 15:23, Shriram Krishnamurthi <<a href="mailto:sk@cs.brown.edu">sk@cs.brown.edu</a>> wrote: > > Hi, > > > > That would not be considered an "example" for at least two reasons. Do you see why? > > > > > >> On Nov 9, 2010 12:17 PM, "Peter Breitsprecher" <<a href="mailto:pkbreits@lakeheadu.ca">pkbreits@lakeheadu.ca</a>> wrote: > >> > >> As an example, I want have most of the functions for Plus, Minus already written. > >> > >> Here is the code for it. > >> > >> (define (plus num1 num2) > >> (+ num1 num2)) > >> > >> That is childs stuff...  Here is where I am having the problem, and please keep in mind I am new to DrRacket... > >> > >> If my program accepts input such as > >> (plus 13 5) > >> > >> I need to parse it so that I know what it is asking for.  If It is a left parent, then I need to move on, if it is a right parent, move on to the next character, once i get to the next character I can see it is an alphanumeric character, but then I need to somehow read the whole word, so that I can store that value in a variable so that I can read the next number.  If the numbers are single digits, it is easy, because they are only one charater each and read-char works perfect, but I need something like a read-word, or read-number and I can't seem to figure out how to do it. > >> > >> So really I need to know how do I read the words when there are characters present, and read the whole numbers when there is a number present. > >> > >> > >> > >> On 9 November 2010 15:00, John Clements <<a href="mailto:clements@brinckerhoff.org">clements@brinckerhoff.org</a>> wrote: > >> > > >> > > >> > On Nov 9, 2010, a... > >> > >> -- > >> Kurt Breitsprecher > >> (807) 474-9601 > >> <a href="mailto:pkbreits@lakeheadu.ca">pkbreits@lakeheadu.ca</a> > >> > >> > >> _________________________________________________ > >>  For list-related administrative tasks: > >>  <a href="http://lists.racket-lang.org/listinfo/users" target="_blank">http://lists.racket-lang.org/listinfo/users</a> > > > > > > > > -- > > Kurt Breitsprecher > > (807) 474-9601 > > <a href="mailto:pkbreits@lakeheadu.ca">pkbreits@lakeheadu.ca</a> > > > > > > > -- > Kurt Breitsprecher > (807) 474-9601 > <a href="mailto:pkbreits@lakeheadu.ca">pkbreits@lakeheadu.ca</a> > </div></div></blockquote></div> -- <div>Kurt Breitsprecher</div> <div>(807) 474-9601</div> <div><a href="mailto:pkbreits@lakeheadu.ca" target="_blank">pkbreits@lakeheadu.ca</a></div>