tricu

A lazy functional language based on Tree Calculus
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state.tri (728B)

      1 !import io as IO
      2 !export pure
      3 !export bind
      4 !export lift
      5 !export current
      6 !export replace
      7 !export io
      8 
      9 -- Sequential test-only state transformer over IO. Each action is a function
     10 -- from explicit state to IO [value nextState]; no host state or concurrency.
     11 pure value state = IO.pure [value state]
     12 bind action next state = IO.bind (action state) (reply : case reply of
     13   [value following] = next value following
     14   _ = IO.fail "Invalid test state action")
     15 lift action state = IO.bind action (value : IO.pure [value state])
     16 current state = IO.pure [state state]
     17 replace value _ = IO.pure [t value]
     18 io action = IO.io (IO.bind (action []) (reply : case reply of
     19   [value _] = IO.pure value
     20   _ = IO.fail "Invalid test state action"))