Dynamic Spreadsheet Assignment

Code To Use

• #t true
• #f false
• define-syntax
• lambda
• procedure?
• procedure-arity number of arguments a function takes Arity on Wikipedia
• pair?
• cons
• car
• cdr
• values
• raise

Code To Implement

file:	src/main/racket/spreadsheet/spreadsheet.rkt
functions:	to-cell csv->spreadsheet row-count row-at sheet sum-row

to-cell

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

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

csv->spreadsheet

define a MACRO thunk-that which takes a parameter e creates thunk. that is: wraps e in a zero argument function.

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

Thunks are useful for delaying the evaluation of expressions. As such thunk-that must be declared as a macro and not a function. Unlike Haskell which has lazy evaluation, Racket (and most other languages) eagerly evaluates function arguments.

row-count

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

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

If thunking and expression wraps an expression in a single argument function, then de-thunking is simply calling that function.

If the parameter thunk is not a thunk? then dethunk-that should raise an argument error.

NOTE: It may seem unnecessary to use dethunk-that when implementing Lab4, when you could simply (thunk)... that is "call the thunk". Still, you are encouraged to use dethunk-that as a bit of verbosity can sometimes help in debugging a sea already full of parentheses.

sum-row

define a function destream which takes a stream parameter and a pair of the next answer and the next stream.

(define (destream stream)
   (error 'not-yet-implemented))

A critical value of this utility function is to provide early error detection. As such, exceptions should be raised if either

• the parameter s is not a thunk (this can be handled by dethunk-that)
• the result of de-thunking the stream is not a pair
• next-stream of the pair is not thunk

stream-cons-ensuring-stream-prime-is-thunk

Define a function cons-with-thunk-check-on-next-stream which takes two parameters value and next-stream.

((define (cons-with-thunk-check-on-next-stream element next-stream)
  (error 'not-yet-implemented))

If the specified next-stream parameter is not a thunk then an error should be raised:

(raise-argument-error "next-stream" "thunk?" next-stream)

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

Test

file:	spreadsheet_test.rkt	Test
source folder:	src/test/racket/spreadsheet

note: ensure that you have removed all printing to receive credit for any assignment.