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;'<<SPEC'

<!--
Copyright (c) 2012-2024, Chris Pressey, Cat's Eye Technologies.
This file is distributed under a 2-clause BSD license.  See LICENSES/ dir.
SPDX-License-Identifier: LicenseRef-BSD-2-Clause-X-Robin
-->

### `extend` ###

    -> Tests for functionality "Evaluate Robin Expression (with List)"

`extend` evaluates its first two arguments to values of any type, and its
third argument to obtain an alist.  It returns a new alist which
associates the first two values in a new pair.  The new pair shadows
any existing pairs with the same key that may already be in the alist.

    | (extend (literal b) 6 (literal ((a 1) (b 2) (c 3))))
    = ((b 6) (a 1) (b 2) (c 3))

The following should be true for any identifier i and alist x.

    | (let ((i (literal a))
    |       (x (literal ((f 5) (g 7)))))
    |   (lookup i (extend i 1 x)))
    = (1)

    | (extend (literal b) 6 ())
    = ((b 6))

    | (extend (literal b) 6 81)
    ? abort (expected-list 81)

'<<SPEC'

(define extend (fun (id val alist)
  (prepend (list id val) alist)))