Clean's type system.

[Arjan van IJzendoorn]

Hello Nick,

>jump :: Addr State -> State.
>
>A more elegant way of looking at jump is as a function that takes an address
>and ruturns an Instruction. Thus,
>
>jump :: Addr -> Instruction.
>
>"Unfortunately, the Clean type system does not allow us to write [this]" (p.
>257).

Clean's type system DOES allow you to write this. It only enforces
that the arity of the type is the same as the arity of the definition.
I don't know what jump does, but you can write something like:

jump :: Addr -> Instruction
jump address = \state -> changePC state
  where
    changePC state = ....

Or you can write...

jump :: Addr -> Instruction
jump address = realJump
  where
    realJump state = changePC state
    changePC state = ....do something with address...

...if you do not like lambda-expressions.

Greetings,
 Arjan