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<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">If I were trying to do something like creating types like….<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">> {-# LANGUAGE DataKinds #-}<o:p></o:p></p>
<p class="MsoNormal">> {-# LANGUAGE ExplicitForAll #-}<o:p></o:p></p>
<p class="MsoNormal">> {-# LANGUAGE FlexibleContexts #-}<o:p></o:p></p>
<p class="MsoNormal">> {-# LANGUAGE FlexibleInstances #-}<o:p></o:p></p>
<p class="MsoNormal">> {-# LANGUAGE GADTs #-}<o:p></o:p></p>
<p class="MsoNormal">> {-# LANGUAGE MultiParamTypeClasses #-}<o:p></o:p></p>
<p class="MsoNormal">> {-# LANGUAGE PolyKinds #-}<o:p></o:p></p>
<p class="MsoNormal">> {-# LANGUAGE StandaloneDeriving #-}<o:p></o:p></p>
<p class="MsoNormal">> {-# LANGUAGE TypeFamilies #-}<o:p></o:p></p>
<p class="MsoNormal">> {-# LANGUAGE TypeOperators #-}<o:p></o:p></p>
<p class="MsoNormal">> {-# LANGUAGE UndecidableInstances #-}<o:p></o:p></p>
<p class="MsoNormal">> {-# LANGUAGE ScopedTypeVariables #-}<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">> data MyList a where<o:p></o:p></p>
<p class="MsoNormal">> MyEnd :: MyList '[]<o:p></o:p></p>
<p class="MsoNormal">> MyCons :: a -> MyList b -> MyList (a ': b)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">> mysimplelist :: MyList '[Integer]<o:p></o:p></p>
<p class="MsoNormal">> mysimplelist = MyCons 1 (MyEnd)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">what about <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">> myrecursivelist = MyCons 1 myrecursivelist<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:Consolas;color:#AF0000">Cafe2.lhs:23:30:<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:Consolas;color:#AF0000"> Occurs check: cannot construct the infinite type: b ~ a : b<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:Consolas;color:#AF0000"> Expected type: MyList b<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:Consolas;color:#AF0000"> Actual type: MyList (a : b)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:Consolas;color:#AF0000"> Relevant bindings include<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:Consolas;color:#AF0000"> myrecursivelist :: MyList (a : b) (bound at Cafe2.lhs:23:3)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:Consolas;color:#AF0000"> In the second argument of ‘MyCons’, namely ‘myrecursivelist’<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:Consolas;color:#AF0000"> In the expression: MyCons 1 myrecursivelist<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">can I “fix” this somehow?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I obviously want the type of myrecursivelist to be <o:p></o:p></p>
<p class="MsoNormal">MyList ‘[Integer, Integer, Integer, Integer, Integer, Integer, Integer, Integer,…..]<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Something like a completely nonsensical…<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">MyList (Fix (Integer ‘: ))<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">P.S.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Yes, I barely understand “fix” as a function, let alone a data type.<o:p></o:p></p>
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