40d9235b3f
There's a bit of a trade off here. It would be better to report the ambiguity but this would lead to a need for (I think) excessive precision in types which would impact usability. It will always take the leftmost interface. Chapter 7 tests added.
2.6 KiB
Type Driven Development with Idris
The code in the book "Type Driven Development with Idris" by Edwin Brady, published by 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).
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:
import Data.Strings -- for `words`
import Data.List -- for `length` on lists
In AveMain.idr and Reverse.idr add:
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:
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:
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:
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:
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:
Abs ty => Abs (Expr ty) where
abs = Abs
Chapter 8
TODO
Chapter 9
TODO
Chapter 10
TODO
Chapter 11
TODO
Chapter 12
TODO
Chapter 13
TODO
Chapter 14
TODO
Chapter 15
TODO