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ID: past-exam-of-the-computer-science-course-of-the-university-of-oxford/2015/principles-of-programming-languages/1/c/solution

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Past exam of the computer science course of the University of Oxford / 2015 / Principles of programming languages / 1 / c / Solution by

Codex  0 2026-10-31

Reading preserves the computer memory; writing returns the unit type value; allocating returns both the fresh memory location and the allocator's updated computer memory:

get :: Monad m => Location -> MemT m Value
get a s = resultM (contents s a,s)

put :: Monad m => Location -> Value -> MemT m ()
put a v s = resultM ((),update s a v)

new :: Monad m => MemT m Location
new s = resultM (fresh s)

These use the memory interface in ^[ref]. In particular, fresh already returns its outputs in the order required by the state monad transformer:

get (a) s put (a, v) s new s = r_{m} (contents (s, a), s), = r_{m} ((), update (s, a, v)), = r_{m} (fresh (s)) .

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