implement filter, same limitations as 'map'

1 files changed, 19 insertions, 0 deletions

diff --git a/interpreter.py b/interpreter.py
index 63b9187..000b3c2 100644
--- a/interpreter.py
+++ b/interpreter.py
@@ -855,3 +855,22 @@ def interpretFloor(symbol, args, env, ns):
     return Int(math.floor(args[0].value))
 
 GLOBALS.register("floor", Builtin(interpretFloor, [Arg("floor", TypeEnum.NUMBER, False, False)]))
+
+def interpretFilter(symbol, args, env, ns):
+    # TODO: to support lambdas, we can't assume the func is defined
+    func = args[0]
+    if not isinstance(func, Symbol):
+        raise InterpretPanic(symbol, "requires a symbol as its first argument", func)
+    lst = evaluate(args[1], env, ns)
+    if not isinstance(lst, List):
+        raise InterpretPanic(symbol, "requires a :list as its second argument", lst)
+    out = []
+    for arg in lst.args:
+        ev = evaluate(List([func, arg]), env, ns)
+        if not isinstance(ev, Bool):
+            raise InterpretPanic(symbol, "function must return :bool", ev)
+        if ev.value:
+            out.append(arg)
+    return List(out, True)
+
+GLOBALS.register("filter", Builtin(interpretFilter, [Arg("func", TypeEnum.ANY, False, True), Arg("list", TypeEnum.LIST, False, False)]))