implement branch

1 files changed, 13 insertions, 0 deletions

diff --git a/interpreter.py b/interpreter.py
index ee7069c..4677432 100644
--- a/interpreter.py
+++ b/interpreter.py
@@ -291,6 +291,19 @@ def interpretPipe(expr, env):
 
 GLOBALS.register("|", Builtin(interpretPipe))
 
+def interpretBranch(expr, env):
+    if len(expr.args) == 0:
+        raise Exception("'branch' takes at least one expression")
+    for arg in expr.args:
+        if len(arg.args) != 1:
+            raise Exception("'branch' branches have two expressions")
+        cond = evaluate(arg.symbol, env)  # this is the condition
+        if cond:
+            return evaluate(arg.args[0], env)
+    return None
+
+GLOBALS.register("branch", Builtin(interpretBranch))
+
 def interpretEnv(expr, env_expr, env):
     ev = evaluate(env_expr, env)
     return ev  # TODO more than this?