From 0adc1abd5088fd51068edda9afa859b6da6b8b1b Mon Sep 17 00:00:00 2001
From: Veit Heller <veit@veitheller.de>
Date: Thu, 8 Jul 2021 20:43:48 +0200
Subject: [PATCH] feat: allow for multibranches in case (#1276)

---
 core/ControlMacros.carp | 18 ++++++++++++++----
 core/Gensym.carp        |  2 +-
 test/macros.carp        |  9 +++++++++
 3 files changed, 24 insertions(+), 5 deletions(-)

diff --git a/core/ControlMacros.carp b/core/ControlMacros.carp
index 327f56bf..fed5d864 100644
--- a/core/ControlMacros.carp
+++ b/core/ControlMacros.carp
@@ -141,6 +141,12 @@ Example:
 (defmacro unless [condition form]
   (list 'if condition (list) form))
 
+(hidden treat-case-handler)
+(defndynamic treat-case-handler [name handler]
+  (if (and (list? handler) (> (length handler) 1) (= ':or (car handler)))
+    (cons 'or (map (fn [val] (list '= name val)) (cdr handler)))
+    (list '= name handler)))
+
 (hidden case-internal)
 (defndynamic case-internal [name xs]
   (if (= (length xs) 0)
@@ -150,24 +156,28 @@ Example:
       (if (= (length xs) 1)
         (car xs)
         (list 'if
-              (list '= name (car xs))
+              (treat-case-handler name (car xs))
               (cadr xs)
               (case-internal name (cddr xs)))))))
 
 (doc case "takes a form and a list of branches which are value and operation
-pairs. If a value matches, the operation is executed. It takes a catch-all else
-branch that is executed if nothing matches.
+pairs. If a value matches (or any in a list of values preced by `:or`), the
+operation is executed. It takes a catch-all else branch that is executed if
+nothing matches.
 
 Example:
 ```
 (case (+ 10 1)
   10 (println* \"nope\")
   11 (println* \"yup\")
+  (:or 12 13) (println* \"multibranch, but nope\")
   (println* \"else branch\")
 )
 ```")
 (defmacro case [form :rest branches]
-  (case-internal form branches))
+  (let [name (gensym)]
+    (list 'let [name form]
+      (case-internal name branches))))
 
 (defmodule Dynamic
   (doc flip
diff --git a/core/Gensym.carp b/core/Gensym.carp
index 78b91bd6..438c17ef 100644
--- a/core/Gensym.carp
+++ b/core/Gensym.carp
@@ -7,7 +7,7 @@
 (doc gensym-with "Generates symbols dynamically, based on a symbol name.")
 (defndynamic gensym-with [x]
   (do
-    (set! *gensym-counter* (inc *gensym-counter*))
+    (set! *gensym-counter* (+ *gensym-counter* 1))
     (Symbol.concat [x (Symbol.from *gensym-counter*)])))
 
 (doc gensym "Generates symbols dynamically as needed.")
diff --git a/test/macros.carp b/test/macros.carp
index 44734f2e..e4466ad6 100644
--- a/test/macros.carp
+++ b/test/macros.carp
@@ -34,6 +34,12 @@
     1 true
     false))
 
+(defn test-case-multi []
+  (case 1
+    2 false
+    (:or 1 3) true
+    false))
+
 (defmacro test-not [a] (not a))
 (defmacro test-< [a b] (< a b))
 (defmacro test-> [a b] (> a b))
@@ -84,6 +90,9 @@
   (assert-true test
                (test-case-select)
                "case correctly selects branch")
+  (assert-true test
+               (test-case-multi)
+               "case correctly selects multibranch")
   (assert-true test
                (test-comment)
                "comment ignores input")