Define Haskell type with multiple contained types -

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my goal replace signature like

execute :: [instruction] -> state -> pointer -> state

with

execute :: program -> state

i created type synonym

type program = [instruction] -> state -> pointer

when define implementation (e.g. execute [] s _ = s), receive following compile error:

couldn't match expected type ‘state -> pointer -> state’             actual type ‘[int]’ equation(s) ‘execute’ have 3 arguments, type ‘program -> state’ has 1

without replacing [instruction] -> state -> pointer program, compiles. appears attempt match program type first argument. there way match program type on first 3 arguments?

your type synonym function type (of 2 arguments, uncurried). when have function

fun :: programm -> state fun p = ...

that p function needs 2 arguments, namely 1 [instruction] , 1 state produce pointer. function, not needed instructions nor state. (and no pointer, if can computed instructions , state, why have parameter original function...)

what seem want packing 3 arguments one. tuple therefore:

type program = ([instruction], state, pointer)

or use record syntax:

data program = program {   instructionsof :: [instruction],   stateof :: state,   pointerof :: pointer }

then code comes closer english:

fun :: program -> state fun program = run (instructionsof program)  -- or whatever

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