You were scooped in 1985... https://link.springer.com/chapter/10.1007%2F3-540-15975-4_33 https://link.springer.com/chapter/10.1007%2F3-540-15975-4_33 Note that

You were scooped in 1985... https://link.springer.com/chapter/10.1007%2F3-540-15975-4_33 https://link.springer.com/chapter/10.1007%2F3-540-15975-4_33 Note that Philip Wadler was active in the Haskell committee. Early versions of Haskell did use a system like that. It was too error-prone. Monadic IO turned out to be theoretically equivalent, but without the easy ways to break it. See https://www.microsoft.com/en-us/research/wp-content/uploads/2016/07/history.pdf https://www.microsoft.com/en-us/research/wp-content/uploads/... for more details.