Subject: bug#74031: [PATCH] srfi-64: Accept complex numbers in test-approximate.

From: Tomas Volf <[email-masked]>
Date: Sat, 26 Oct 2024 18:07:06 +0200

The specification mandates reals, but the reference implementation
supports complex numbers.  So as implementation extension, support them
as well.

* module/srfi/srfi-64.scm (within-epsilon): Support complex arguments.
---
Proposal for how to extend test-approximate to handle complex arguments.
However it differs from the original one.  That one expected `error' to be a
real number, and used it for comparing both real parts and imaginary parts.

To me, that seems weird.  I would consider it useful to be able to have
different errors for real and imaginary parts.

However I cannot remember the last time I have used complex numbers, so I am not
sure I am qualified to have an opinion here.  What do other people think?

 module/srfi/srfi-64.scm | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/module/srfi/srfi-64.scm b/module/srfi/srfi-64.scm
index 1f60a72e5..5fc23e28a 100644
--- a/module/srfi/srfi-64.scm
+++ b/module/srfi/srfi-64.scm
@@ -776,8 +776,16 @@ Test whether result of @var{test-expr} matches @var{expected} using

 (define (within-epsilon ε)
   (λ (expected actual)
-    (and (>= actual (- expected ε))
-         (<= actual (+ expected ε)))))
+    (let ((e-r (real-part expected))
+          (e-i (imag-part expected))
+          (a-r (real-part actual))
+          (a-i (imag-part actual))
+          (ε-r (real-part ε))
+          (ε-i (imag-part ε)))
+      (and (>= a-r (- e-r ε-r))
+           (<= a-r (+ e-r ε-r))
+           (>= a-i (- e-i ε-i))
+           (<= a-i (+ e-i ε-i))))))

 (define-syntax %test-approximate
   (λ (x)
@@ -808,6 +816,10 @@ Test whether result of @var{test-expr} matches @var{expected} using
 Test whether result of @var{test-expr} is within @var{error} of
 @var{expected}.

+As implementation extension, complex numbers are supported as well.  It tests
+whether real parts are within @code{(real-part @var{error})}, and imaginary
+parts within @code{(imag-part @var{error})}.
+
 @end defspec")

 (define-syntax %test-error
--
2.46.0