.. _typedd-index: Type Driven Development with Idris: Updates Required ==================================================== The code in the book `Type-Driven Development with Idris `_ by Edwin Brady, available from `Manning `_, will mostly work in Idris 2, with some small changes as detailed in this document. The updated code is also [going to be] part of the test suite (see `tests/typedd-book `_ in the Idris 2 source). Chapter 1 --------- No changes necessary Chapter 2 --------- The Prelude is smaller than Idris 1, and many functions have been moved to the base libraries instead. So: In ``Average.idr``, add: .. code-block:: idris import Data.Strings -- for `words` import Data.List -- for `length` on lists In ``AveMain.idr`` and ``Reverse.idr`` add: .. code-block:: idris import System.REPL -- for 'repl' Chapter 3 --------- Unbound implicits have multiplicity 0, so we can't match on them at run-time. Therefore, in ``Matrix.idr``, we need to change the type of ``createEmpties`` and ``transposeMat`` so that the length of the inner vector is available to match on: .. code-block:: idris createEmpties : {n : _} -> Vect n (Vect 0 elem) transposeMat : {n : _} -> Vect m (Vect n elem) -> Vect n (Vect m elem) Chapter 4 --------- For the reasons described above: + In ``DataStore.idr``, add ``import System.REPL`` and ``import Data.Strings`` + In ``SumInputs.idr``, add ``import System.REPL`` + In ``TryIndex.idr``, add an implicit argument: .. code-block:: idris tryIndex : {n : _} -> Integer -> Vect n a -> Maybe a Chapter 5 --------- There is no longer a ``Cast`` instance from ``String`` to ``Nat``, because its behaviour of returing Z if the ``String`` wasn't numeric was thought to be confusing. Instead, there is ``stringToNatOrZ`` in ``Data.Strings`` which at least has a clearer name. So: In ``Loops.idr`` and ``ReadNum.idr`` add ``import Data.Strings`` and change ``cast`` to ``stringToNatOrZ`` Chapter 6 --------- In ``DataStore.idr`` and ``DataStoreHoles.idr``, add ``import Data.Strings`` and ``import System.REPL``. Also in ``DataStore.idr``, the ``schema`` argument to ``display`` is required for matching, so change the type to: .. code-block:: idris display : {schema : _} -> SchemaType schema -> String In ``TypeFuns.idr`` add ``import Data.Strings`` Chapter 7 --------- ``Abs`` is now a separate interface from ``Neg``. So, change the type of ``eval`` to include ``Abs`` specifically: .. code-block:: idris eval : (Abs num, Neg num, Integral num) => Expr num -> num Also, take ``abs`` out of the ``Neg`` implementation for ``Expr`` and add an implementation of ``Abs`` as follows: .. code-block:: idris Abs ty => Abs (Expr ty) where abs = Abs Chapter 8 --------- In ``AppendVec.idr``, add ``import Data.Nat`` for the ``Nat`` proofs ``cong`` now takes an explicit argument for the function to apply. So, in ``CheckEqMaybe.idr`` change the last case to: .. code-block:: idris checkEqNat (S k) (S j) = case checkEqNat k j of Nothing => Nothing Just prf => Just (cong S prf) A similar change is necessary in ``CheckEqDec.idr``. In ``ExactLength.idr``, the ``m`` argument to ``exactLength`` is needed at run time, so change its type to: .. code-block:: idris exactLength : {m : _} -> (len : Nat) -> (input : Vect m a) -> Maybe (Vect len a) A similar change is necessary in ``ExactLengthDec.idr``. Also, ``DecEq`` is no longer part of the prelude, so add ``import Decidable.Equality``. In ``ReverseVec.idr``, add ``import Data.Nat`` for the ``Nat`` proofs. Chapter 9 --------- + In ``ElemType.idr``, add ``import Decidable.Equality`` In ``Hangman.idr``: + Add ``import Decidable.Equality`` and ``import Data.Strings`` + ``removeElem`` pattern matches on ``n``, so it needs to be written in its type: .. code-block:: idris removeElem : {n : _} -> (value : a) -> (xs : Vect (S n) a) -> {auto prf : Elem value xs} -> Vect n a + ``letters`` is used by ``processGuess``, because it's passed to ``removeElem``: .. code-block:: idris processGuess : {letters : _} -> (letter : Char) -> WordState (S guesses) (S letters) -> Either (WordState guesses (S letters)) (WordState (S guesses) letters) + ``guesses`` and ``letters`` are implicit arguments to ``game``, but are used by the definition, so add them to its type: .. code-block:: idris game : {guesses : _} -> {letters : _} -> WordState (S guesses) (S letters) -> IO Finished In ``RemoveElem.idr`` + ``removeElem`` needs to be updated as above. Chapter 10 ---------- Lots of changes necessary here, at least when constructing views, due to Idris 2 having a better (that is, more precise and correct!) implementation of unification, and the rules for recursive ``with`` application being tightened up. In ``MergeSort.idr``, add ``import Data.List`` In ``MergeSortView.idr``, add ``import Data.List``, and make the arguments to the views explicit: .. code-block:: idris mergeSort : Ord a => List a -> List a mergeSort input with (splitRec input) mergeSort [] | SplitRecNil = [] mergeSort [x] | SplitRecOne x = [x] mergeSort (lefts ++ rights) | (SplitRecPair lefts rights lrec rrec) = merge (mergeSort lefts | lrec) (mergeSort rights | rrec) In ``SnocList.idr``, in ``my_reverse``, the link between ``Snoc rec`` and ``xs ++ [x]`` needs to be made explicit. Idris 1 would happily decide that ``xs`` and ``x`` were the relevant implicit arguments to ``Snoc`` but this was little more than a guess based on what would make it type check, whereas Idris 2 is more precise in what it allows to unify. So, ``x`` and ``xs`` need to be explicit arguments to ``Snoc``: .. code-block:: idris data SnocList : List a -> Type where Empty : SnocList [] Snoc : (x, xs : _) -> (rec : SnocList xs) -> SnocList (xs ++ [x]) Correspondingly, they need to be explicit when matching. For example: .. code-block:: idris my_reverse : List a -> List a my_reverse input with (snocList input) my_reverse [] | Empty = [] my_reverse (xs ++ [x]) | (Snoc x xs rec) = x :: my_reverse xs | rec Similar changes are necessary in ``snocListHelp`` and ``my_reverse_help``. See tests/typedd-book/chapter10/SnocList.idr for the full details. Also, in ``snocListHelp``, ``input`` is used at run time so needs to be bound in the type: .. code-block:: idris snocListHelp : {input : _} -> (snoc : SnocList input) -> (rest : List a) -> SnocList (input + It's no longer necessary to give ``{input}`` explicitly in the patterns for ``snocListHelp``, although it's harmless to do so. In ``IsSuffix.idr``, the matching has to be written slightly differently. The recursive with application in Idris 1 probably shouldn't have allowed this! .. code-block:: idris isSuffix : Eq a => List a -> List a -> Bool isSuffix input1 input2 with (snocList input1, snocList input2) isSuffix [] input2 | (Empty, s) = True isSuffix input1 [] | (s, Empty) = False isSuffix (xs ++ [x]) (ys ++ [y]) | (Snoc xsrec, Snoc ysrec) = if x == y then isSuffix xs ys | (xsrec, ysrec) else False This doesn't yet get past the totality checker, however, because it doesn't know about looking inside pairs. In ``DataStore.idr``: Well this is embarrassing - I've no idea how Idris 1 lets this through! I think perhaps it's too "helpful" when solving unification problems. To fix it, add an extra parameter ``scheme`` to ``StoreView``, and change the type of ``SNil`` to be explicit that the ``empty`` is the function defined in ``DataStore``. Also add ``entry`` and ``store`` as explicit arguments to ``SAdd``: .. code-block:: idris data StoreView : (schema : _) -> DataStore schema -> Type where SNil : StoreView schema DataStore.empty SAdd : (entry, store : _) -> (rec : StoreView schema store) -> StoreView schema (addToStore entry store) Since ``size`` is as explicit argument in the ``DataStore`` record, it also needs to be relevant in the type of ``storeViewHelp``: .. code-block:: idris storeViewHelp : {size : _} -> (items : Vect size (SchemaType schema)) -> StoreView schema (MkData size items) In ``TestStore.idr``: + In ``listItems``, ``empty`` needs to be ``DataStore.empty`` to be explicit that you mean the function + In ``filterKeys``, there is an error in the ``SNil`` case, which wasn't caught because of the type of ``SNil`` above. It should be: .. code-block:: idris filterKeys test DataStore.empty | SNil = [] Chapter 11 ---------- Remove ``%default total`` throughout - it's not yet implemented. In ``Streams.idr`` add ``import Data.Stream`` for ``iterate``. In ``Arith.idr`` and ``ArithTotal.idr``, the ``Divides`` view now has explicit arguments for the dividend and remainder, so they need to be explicit in ``bound``: .. code-block:: idris bound : Int -> Int bound x with (divides x 12) bound ((12 * div) + rem) | (DivBy div rem prf) = rem + 1 In ``ArithCmd.idr``, update ``DivBy`` as above. Also add ``import Data.Strings`` for ``Strings.toLower``. In ``ArithCmd.idr``, update ``DivBy`` and ``import Data.Strings`` as above. Also, since export rules are per-namespace now, rather than per-file, you need to export ``(>>=)`` from the namespaces ``CommandDo`` and ``ConsoleDo``. Chapter 12 ---------- Remove ``%default total`` throughout, at least until it's implemented. For reasons described above: In ``ArithState.idr``, add ``import Data.Strings``. Also the ``(>>=)`` operators need to be set as ``export`` since they are in their own namespaces, and in ``getRandom``, ``DivBy`` needs to take additional arguments ``div`` and ``rem``. Chapter 13 ---------- TODO Chapter 14 ---------- TODO Chapter 15 ---------- TODO