CODEWITHSUNDEEP
functional-programmingschemeracketpolynomials
Mohammad Arshad
Mohammad Arshad

Reputation: 25

Convert a polynomial represented as a list of coefficients to a string

I know this is a newbish question. I am trying to create a function 'displayPoly' to display a polynomial in scheme. For example a list given as '(2 0 1 5.1 8) should display 2x^4 + x^2 + 5.1x + 8.

I have defined "degree" as the following: 

 (define degree
 (lambda(list)
  (if (null? list) 
      (- 1)
  (+ 1  (degree (cdr list))))))

Please note I am strictly limited to basic scheme functions •define, lambda, if, cond, cons,car, cdr, list , member, list-ref •predicates : null? list? equal? string? number? member? •arithmetic operators , relational operators, logical operators •sort, map, filter, foldr, foldl, length, reverse, append, last , let, let*, letrec, print, begin, newline, display, expt, string-append, reduce, range

Upvotes: 1

Views: 1196

Answers (1)

soegaard
soegaard

Reputation: 31147

You need to write some helper functions.

  1. Write a function that given a polynomial returns a list of the degrees.

    Input: '(2 0 1 5.1 8) Output: (4 3 2 1 0)

  2. Write a function mono that given a coefficient and a degree outputs a monomial as a string.

    Input: 2 4 Output: "2x^4"

  3. Use (map mono '(2 0 1 5.1 8) (4 3 2 1 0)) to produce a list of the monomials.

  4. Use add-between (or write one yourself) to add "+" between all your monomials.

  5. Use (apply string-append your-list-of-monomials) to get you final string.

Note: It's possible to produce prettier output, but this is a good start.

Upvotes: 1

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