Thunks and Streams Assignment

Motivation

It is all too easy to make a simple mistake on the 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

define-syntax

lambda

procedure?

procedure-arity

pair?

cons

car

cdr

Code To Implement

file:	src/main/racket/hw4/hw4.rkt
functions:	thunk? thunk-that dethunk-that ...

Thunk Utilities

thunk?

define a function thunk? which returns whether the specified parameter is a thunk or not.

(define (thunk? th)
    (error 'not-yet-implemented))

true: #t

false: #f

is a function: procedure?

number of parameters: procedure-arity

thunk-that

define a MACRO thunk-that which creates thunk

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

dethunk-that

define a function dethunk which takes a thunk parameter th and returns the result of invoking th.

(define (dethunk-that e)
   (error 'not-yet-implemented))

Stream Utilities

plausible-stream?

define a function plausible-stream? 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 plausible-stream? recursively on the cdr?

next-value-from-stream

define a function next-value-from-stream which takes a stream parameter and returns the next value of that stream.

next-stream-from-stream

define a function next-stream-from-stream 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 stream-next which takes a stream parameter and returns a pair of values for the next value and the next stream.

stream-cons

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

(raise (error "not a thunk" stream-prime))

If stream-prime is a thunk it should simply cons value and stream-prime. Do NOT create a thunk.

WARNING: what could happen if you called plausible-stream? on stream-prime?

Stream App

flip-flop-stream

define flip-flop-stream which produces #t #f #t #f #t #f #t #f...