Wadler's Blog

In the downloads for the paper "How to make ad-hoc
polymorphism less ad hoc" available here:

http://homepages.inf.ed.ac.uk/wadler/topics/type-classes.html

...there seems to be a typo on page 7, figure 4 ("Translation of
equality")--I believe

eqDChar :: EqD Int

should read

eqDChar :: EqD Char

Thanks!
 

Marriage of Monads and Effects

homepages.inf.ed.ac.uk/wadler/papers/effectstocl/effectstocl.pdf

In the conclusions section:


Here one might define T σ τ = S_σ → X ×S^σ where S_σ is a store restricted to contain only locations in regions ρ such that read(ρ) or init(ρ) is in σ, and S^σ is a store restricted to contain only locations in regions ρ such that init(ρ) or write(ρ) is in σ.


S^σ (the returned store) is incorrectly defined, and doesn't in general form a monad (in the expected way). Think how you would define the return for this monad!.

The initialization complicates matters, but assuming σ does not contain init(ρ), S^σ should be defined along the following lines:

S^σ = S1(σ)*(1+S2(σ))

where S1(σ) is the store restricted to contain only locations in regions ρ such thar both read(ρ) and write(ρ) are in σ,
and S2(σ) is store restricted to contain only locations in regions ρ such thar only write(ρ) is in σ,
 

Monads for functional programming

http://homepages.inf.ed.ac.uk/wadler/papers/marktoberdorf/baastad.pdf

In the section 3 where the paper explains the Monad Laws (3) there is an example of the evaluator code as addition rather than division but it's incorrectly shown as division again.

"eval (Add t u) = eval t ⋆ λa. eval u ⋆ λb. unit (a ÷ b)"

In part 4r there's a typo "can be use to manipulate extenal state" (instead of external state).