I am now onto the mutations chapter.
It seems that Decimal has changed it’s parse return. It used to be {:ok, decimal}
but is now {decimal, remainder}
which means that you will need the following to get Chapter 5 to build:
scalar :decimal do
parse fn
%{value: value}, _ ->
{d,_} = Decimal.parse(value)
{:ok, d}
_, _ ->
:error
end
serialize &to_string/1
end