erlang, factor, rust: fix empty list eval

This should address remaining implementation fixes for #194.

erlang/src/step2_eval.erl

@@ -43,6 +43,8 @@ read(String) ->
         {error, Reason} -> io:format("error: ~s~n", [Reason]), nil
     end.
 
+eval({list, [], _Meta}=AST, _Env) ->
+    AST;
 eval({list, List, Meta}, Env) ->
     case eval_ast({list, List, Meta}, Env) of
         {list, [F|Args], _M} -> erlang:apply(F, [Args]);

factor/step2_eval/step2_eval.factor

@@ -1,8 +1,8 @@
 ! Copyright (C) 2015 Jordan Lewis.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: accessors arrays assocs combinators continuations fry io
-kernel math lib.printer lib.reader lib.types quotations readline
-sequences ;
+USING: accessors arrays assocs combinators combinators.short-circuit
+continuations fry io kernel math lib.printer lib.reader lib.types
+quotations readline sequences ;
 IN: step2_eval
 
 CONSTANT: repl-env H{
@@ -34,7 +34,7 @@ DEFER: EVAL
 : READ ( str -- maltype ) read-str ;
 
 : EVAL ( maltype env -- maltype )
-    eval-ast dup array? [
+    eval-ast dup { [ array? ] [ empty? not ] } 1&& [
         unclip
         dup quotation? [ "not a fn" throw ] unless
         with-datastack first

rust/src/bin/step2_eval.rs

@@ -54,8 +54,14 @@ fn eval(ast: MalVal, env: &HashMap<String,MalVal>) -> MalRet {
     // apply list
     match *try!(eval_ast(ast, env)) {
         List(ref args,_) => {
-            let ref f = args.clone()[0];
-            f.apply(args[1..].to_vec())
+            match args.len() {
+                0 =>
+                    Ok(list(vec![])),
+                _ =>  {
+                    let ref f = args.clone()[0];
+                    f.apply(args[1..].to_vec())
+                }
+            }
         },
         _ => return err_str("Expected list"),
     }