From d1f378b7ed770f1ad78eb3e748f6ebc6c7024ef3 Mon Sep 17 00:00:00 2001
From: Rose Hogenson <rhogenson@posteo.net>
Date: Tue, 11 Jan 2022 19:49:48 -0800
Subject: Add guards to the match syntax.

I'm not sure the syntax is great, but it's very helpful to have.
---
 match-test.csc | 10 ++++++++++
 match.csc      | 11 ++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/match-test.csc b/match-test.csc
index 73daa58..bbecce4 100644
--- a/match-test.csc
+++ b/match-test.csc
@@ -66,3 +66,13 @@
       ((! 'a) 1)
       ((! 'b) 2)
       (_ 3))))
+
+
+(test match-when
+  (assert-equal
+    3
+    (match 'b
+      ((! 'a) 1)
+      ((! 'b) (when #f) 2)
+      ((! 'b) 3)
+      (_ 4))))
diff --git a/match.csc b/match.csc
index 07ca98c..d188349 100644
--- a/match.csc
+++ b/match.csc
@@ -40,10 +40,19 @@
 
 
     (define-syntax match
-      (syntax-rules ()
+      (syntax-rules (when)
+        ((match x (pattern (when condition) result result* ...))
+         (if (and (matches? x pattern)
+                  condition)
+           (bind-pattern x pattern result result* ...)))
         ((match x (pattern result1 result2 ...))
          (if (matches? x pattern)
            (bind-pattern x pattern result1 result2 ...)))
+        ((match x (pattern (when condition) result result* ...) clause clause* ...)
+         (if (and (matches? x pattern)
+                  condition)
+           (bind-pattern x pattern result result* ...)
+           (match x clause clause* ...)))
         ((match x (pattern result1 result2 ...) clause1 clause2 ...)
          (if (matches? x pattern)
            (bind-pattern x pattern result1 result2 ...)
-- 
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