Please submit using the Fire system

Assignments

  -- computes the sum of all numbers in the list
  sum :: [Integer] -> Integer
  sum []     = 0
  sum (x:xs) = x + sum xs  

  -- appends two lists
  (++) :: [Integer] -> [Integer] -> [Integer]
  []     ++ ys = ys
  (x:xs) ++ ys = x : (xs ++ ys) 

  sum (xs ++ ys) = sum xs + sum ys

  data Expr = Num Integer
            | Add Expr Expr
  
  -- evaluates the expression
  eval :: Expr -> Integer
  eval (Num n)   = n
  eval (Add a b) = eval a + eval b

  -- collects all numbers in the expression
  numbers :: Expr -> [Integer]
  numbers (Num n)   = [n]                 -- [n] is the same as n:[]
  numbers (Add a b) = numbers a ++ numbers b

  sum (numbers x) = eval x

Submission

Submission of this assignment should be done electronically through the Fire system.

The submission deadline is Wednesday, October 14, at 13:00. At this time, you should have submitted a serious attempt to solve the assignment. A serious attempt is either an answer you believe to be correct, or a partial answer plus a detailed explanation of what you have tried to come up with a full answer. An empty document is not a serious attempt.

After submitting, you have until October 26 (midnight) to submit a completely correct version.

You can submit your answers in any of the following formats:

• A simple text file, ending in .txt. You can make text files in any text editor, and then upload it to the Fire system.

  (When using a text file, you may sometimes need to "invent" notation. Please be clear about what your notation means. A list of suggested notation for text files is provided by us. You may also use Unicode.)

• A picture you have made in a painting program, ending in .gif, .jpg, or .png. You can use for example MS Paint, or Google Docs to make a picture, and upload it to the Fire system.

• A PDF-file, ending in .pdf. You can make PDF files by for example using OpenOffice, LibreOffice, Microsoft Word, or Google Docs, and choosing export as PDF. Then, upload the PDF-file to the Fire system.

• A scanned in document, ending in .pdf or .jpg. You can write your answer on a piece of paper, and use a scanner to scan it in and convert to a PDF-file. Or you can use your mobile phone to take pictures of the papers, and upload these to the Fire system.