View source for Thunks and Streams Assignment

=Motivation=
It is all too easy to make a simple mistake on the [[Streams_Assignment|Streams Lab]] and have it burn way to much of ones time.  We will build some utility functions that will hopefully make our code more clear, as well as raise better errors sooner when we make a mistake.

=Code To Use=
[https://docs.racket-lang.org/reference/define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define-syntax%29%29 define-syntax]

[https://docs.racket-lang.org/reference/lambda.html?q=lambda#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29 lambda]

[https://docs.racket-lang.org/reference/procedures.html#%28def._%28%28quote._~23~25kernel%29._procedure~3f%29%29 procedure?]

[https://docs.racket-lang.org/reference/procedures.html?q=procedure-arity#%28def._%28%28quote._~23~25kernel%29._procedure-arity%29%29 procedure-arity]

[https://docs.racket-lang.org/reference/pairs.html?q=cons#%28def._%28%28quote._~23~25kernel%29._pair~3f%29%29 pair?]

[https://docs.racket-lang.org/reference/pairs.html?q=cons#%28def._%28%28quote._~23~25kernel%29._cons%29%29 cons]

[https://docs.racket-lang.org/reference/pairs.html?q=cons#%28def._%28%28quote._~23~25kernel%29._car%29%29 car]

[https://docs.racket-lang.org/reference/pairs.html?q=cons#%28def._%28%28quote._~23~25kernel%29._cdr%29%29 cdr]

=Code To Implement=
{{RacketToImplement|hw4|thunk?<br>thunk-that<br>dethunk-that<br>...|hw4}}
==Thunk Utilities==
===thunk?===
define a function <code>thunk?</code> which returns whether the specified parameter is a [https://en.wikipedia.org/wiki/Thunk thunk] or not.

 <nowiki>(define (thunk? th)
    (error 'not-yet-implemented))</nowiki>

true: [https://docs.racket-lang.org/reference/booleans.html #t]

false: [https://docs.racket-lang.org/reference/booleans.html #f]

is a function: [https://docs.racket-lang.org/reference/procedures.html#%28def._%28%28quote._~23~25kernel%29._procedure~3f%29%29 procedure?]

number of parameters: [https://docs.racket-lang.org/reference/procedures.html?q=procedure-arity#%28def._%28%28quote._~23~25kernel%29._procedure-arity%29%29 procedure-arity]

===thunk-that===
define a '''MACRO''' <code>thunk-that</code> which creates thunk

 (define-syntax-rule (thunk-that e)
    (error 'not-yet-implemented))

===dethunk===
define a function <code>dethunk</code> which takes a thunk parameter <code>th</code> and returns the result of invoking <code>th</code>.

==Stream Utilities==

===plausible-stream?===
define a function <code>plausible-stream?</code> which returns #t if the specified parameter is a thunk which when invoked returns a pair whose cdr is a thunk, #f otherwise.

WARNING: what could happen if you called <code>plausible-stream?</code> recursively on the <code>cdr</code>?

===next-value-from-stream===
define a function <code>next-value-from-stream</code> which takes a stream parameter and returns the next value of that stream.

===next-stream-from-stream===
define a function <code>next-stream-from-stream</code> which takes a stream parameter and returns the next stream of that stream.

===stream-next===
BONUS method not officially part of the studio but a good idea.

define a function <code>stream-next</code> which takes a stream parameter and returns a pair of values for the next value and the next stream.

===stream-cons===
define a function <code>stream-cons</code> which takes two parameters <code>value</code> and <code>stream-prime</code>.  if the specified <code>stream-prime</code> parameter is not a thunk then an error should be raised:

 <code>(raise (error "not a thunk" stream-prime))</code>

If <code>stream-prime</code> is a thunk it should simply [https://docs.racket-lang.org/reference/pairs.html#%28def._%28%28quote._~23~25kernel%29._cons%29%29 cons] <code>value</code> and <code>stream-prime</code>.  Do '''NOT''' create a thunk.

WARNING: what could happen if you called <code>plausible-stream?</code> on <code>stream-prime</code>?

==Stream App==
===flip-flop-stream===
define <code>flip-flop-stream</code> which produces #t #f #t #f #t #f #t #f...