Problem with typeclasses blog post

[bon]

I was reading through the blog post on typeclasses but ran into a problem with the coalton and cl packages. Here's a snippet that fails with the error Unknown binding COMMON-LISP:SQRT

(cl:defpackage :coalton-typeclasses
  (:use :coalton :coalton-library))

(cl:in-package :coalton-typeclasses)

(coalton-toplevel

  (define-type Translation (Trans Single-Float Single-Float))

  (declare distance (Translation -> Single-Float))
  (define (distance t)
    (match t
      ((Trans dx dy) (cl:sqrt (+ (* dx dx) (* dy dy)))))))

It give the same error when replacing the defpackage with (in-package :coalton-user)
I'm using SBCL 2.1.11 with Quicklisp and Coalton updated to today.

[stylewarning]

Sorry, sqrt isn't in the standard library. Add this above the distance definition:

(declare sqrt (Single-Float -> Single-Float))
(define (sqrt x)
  (lisp Single-Float (x)
    (cl:sqrt x)))

I'm not exactly sure where sqrt should go in the standard library yet.