imeraj
Advanced Functional Programming with Elixir: Problem Running Code Example
I am reading this book with great enthusiasm.
So far the code works great but while running the examples in Predicates That Span Contexts section I am encountering some function arity errors as below -
iex(13)> FunPark.Ride.eligible?(alice, tea_cup)
** (FunctionClauseError) no function clause matching in FunPark.Monoid.FunPark.Monoid.PredAll.wrap/2
The following arguments were given to FunPark.Monoid.FunPark.Monoid.PredAll.wrap/2:
# 1
%FunPark.Monoid.PredAll{
value: &FunPark.Monoid.PredAll.default_pred?/1
}
# 2
#Function<1.2796843/2 in FunPark.Ride.tall_enough?>
Attempted function clauses (showing 1 out of 1):
def wrap(%FunPark.Monoid.PredAll{}, value) when is_function(value, 1)
Apparently, we are passing two arguments instead of one here -
def eligible?(%Patron{} = patron, %__MODULE__{} = ride),
do: p_all([&tall_enough?/2, &old_enough?/2]).(patron, ride)
I ran the book’s sample code and it works fine. But it has code with curry.
I am wondering if the example code from this section is supposed to run without curry as I am typing in the code as I go.
Thanks!
First Post!
luistavera
Hi
I am running into the same issue. I think this is an error in the book since the Predicate expects a function with arity 1. The following works:
def elegible?(%Patron{} = patron, %MODULE{} = ride) do
te = fn patron → tall_enough?(patron, ride) end
oe = fn patron → old_enough?(patron, ride) end
p_all([te, oe]).(patron)
end
Cheers
Popular Pragmatic Bookshelf topics
Other popular topics
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /wasm
- /ruby
- /erlang
- /phoenix
- /keyboards
- /python
- /js
- /rails
- /security
- /go
- /swift
- /vim
- /java
- /clojure
- /emacs
- /haskell
- /typescript
- /svelte
- /onivim
- /kotlin
- /c-plus-plus
- /crystal
- /tailwind
- /react
- /gleam
- /ocaml
- /elm
- /vscode
- /flutter
- /html
- /ash
- /deepseek
- /zig
- /opensuse
- /centos
- /php
- /scala
- /react-native
- /lisp
- /textmate
- /sublime-text
- /nixos
- /debian
- /agda
- /deno
- /django
- /kubuntu
- /arch-linux
- /nodejs
- /ubuntu
- /spring
- /revery
- /manjaro
- /diversity
- /julia
- /lua
- /quarkus
- /markdown









