add guard macro

jcubic · Jan 9, 2024 · f3167bf · f3167bf
1 parent a262c11
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,4 +1,6 @@
 ## 1.0.0-beta.18
+### Features
+* add R7RS `guard` macro
 ### Bugfix
 * remove evaluating of async list data as first argument
 

diff --git a/lib/R7RS.scm b/lib/R7RS.scm
@@ -1184,6 +1184,23 @@
        ,@body
        (--> ,parent (set ',name ,module-var)))))
 
+;; -----------------------------------------------------------------------------
+(define-syntax guard
+  (syntax-rules (catch)
+    ((_ (var cond1 cond2 ...)
+        body ...)
+     (try
+       body ...
+       (catch (var)
+              (cond cond1
+                    cond2 ...)))))
+  "(guard (variable (cond result)
+                    (cond2 result))
+          body)
+
+   Macro that executes the body and when there is exception, triggered by
+   raise it's saved in variable that can be tested by conditions.")
+
 ;; -----------------------------------------------------------------------------
 (define-syntax define-library/export
   (syntax-rules (rename :c)