"when" macro for Try.

1 files changed, 15 insertions, 1 deletions

diff --git a/stdlib/source/library/lux/control/try.lux b/stdlib/source/library/lux/control/try.lux
index 4da14bb92..d00d15d28 100644
--- a/stdlib/source/library/lux/control/try.lux
+++ b/stdlib/source/library/lux/control/try.lux
@@ -150,4 +150,18 @@
                                    (~ else))))]}
 
     _
-    {#Failure "Wrong syntax for else"}))
+    {#Failure "Wrong syntax for 'else'"}))
+
+(macro: .public (when tokens state)
+  (case tokens
+    (pattern (.list test then))
+    (let [code#encoded ("lux in-module" "library/lux" .code#encoded)
+          text$ ("lux in-module" "library/lux" .text$)]
+      {.#Right [state (.list (` (.if (~ test)
+                                  (~ then)
+                                  {..#Failure (~ (text$ ($_ "lux text concat"
+                                                            "[" (code#encoded (` .when)) "]"
+                                                            " " "Invalid condition:")))})))]})
+
+    _
+    {.#Left "Wrong syntax for 'when'"}))