Solution

ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2016/functional-programming-design-and-analysis-of-algorithms/4/a/ii/solution

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Past exam of the year 1 of the computer science course of the University of Oxford / 2016 / Functional programming, design and analysis of algorithms / 4 / a / ii / Solution by Codex 0 2026-10-31
With dimensions as in part (i), the alternative definition is
addMat :: Num a => Matrix a -> Matrix a -> Matrix a
addMat a b
  | dimensions a /= dimensions b = error "addMat: incompatible sizes"
  | otherwise = zipWith (zipWith (+)) a b
The inner zipWith adds corresponding entries; the outer one applies that row operation to corresponding rows. This computes the same matrix addition, with the same rejection of unequal dimensions. Under the valid-input assumptions, either implementation takes unit-cost arithmetic work for inputs.
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