Fix empty list eval in step2 for most languages.

I think the only remaining ones are ada, elisp, factor, and rust.

Author: kanaka

bash/step2_eval.sh

@@ -48,6 +48,7 @@ EVAL () {
         EVAL_AST "${ast}" "${env}"
         return
     fi
+    _empty? "${ast}" && r="${ast}" && return
 
     # apply list
     EVAL_AST "${ast}" "${env}"

clojure/src/step2_eval.clj

@@ -32,11 +32,13 @@
       (eval-ast ast env)
 
       ;; apply list
-              ;; indented to match later steps
+            ;; indented to match later steps
+            (if (empty? ast)
+              ast
               (let [el (eval-ast ast env)
                     f (first el)
                     args (rest el)]
-                (apply f args))))
+                (apply f args)))))
 
 ;; print
 (defn PRINT [exp] (pr-str exp))

coffee/step2_eval.coffee

@@ -21,6 +21,7 @@ eval_ast = (ast, env) ->
 EVAL = (ast, env) ->
   #console.log "EVAL:", printer._pr_str ast
   if !types._list_Q ast then return eval_ast ast, env
+  if ast.length == 0 then return ast
 
   # apply list
   [f, args...] = eval_ast ast, env

crystal/step2_eval.cr

@@ -53,7 +53,7 @@ module Mal
   def eval(t, env)
     Mal::Type.new case ast = t.unwrap
     when Mal::List
-      eval_error "empty list" if ast.empty?
+      return gen_type Mal::List if ast.empty?
 
       f = eval_ast(ast.first, env)
       ast.shift(1)

d/step2_eval.d

@@ -57,6 +57,10 @@ MalType EVAL(MalType ast, Env env)
     {
         return eval_ast(ast, env);
     }
+    if ((cast(MalList) ast).elements.length == 0)
+    {
+        return ast;
+    }
 
     auto el = verify_cast!MalList(eval_ast(ast, env));
     auto fobj = verify_cast!MalBuiltinFunc(el.elements[0]);

elixir/lib/mix/tasks/step2_eval.ex

@@ -46,6 +46,7 @@ defmodule Mix.Tasks.Step2Eval do
     Mal.Reader.read_str(input)
   end
 
+  defp eval({:list, [], _} = empty_ast, env), do: empty_ast
   defp eval({:list, ast, meta}, env), do: eval_list(ast, env, meta)
   defp eval(ast, env), do: eval_ast(ast, env)
 

es6/step2_eval.js

@@ -32,6 +32,7 @@ const eval_ast = (ast, env) => {
 
 const EVAL = (ast, env) => {
     if (!_list_Q(ast)) { return eval_ast(ast, env) }
+    if (ast.length === 0) { return ast }
 
     const [f, ...args] = eval_ast(ast, env)
     return f(...args)

forth/step2_eval.fs

@@ -77,8 +77,12 @@ drop
 
 MalList
   extend mal-eval { env list -- val }
-    env list MalList/start @ @ eval
-    env list rot eval-invoke ;;
+    list MalList/count @ 0= if
+        list
+    else
+        env list MalList/start @ @ eval
+        env list rot eval-invoke
+    endif ;;
 drop
 
 MalVector

fsharp/step2_eval.fs

@@ -11,6 +11,7 @@ module REPL
         | node -> node
 
     and eval env = function
+        | List(_, []) as emptyList -> emptyList
         | List(_, _) as node ->
             let resolved = node |> eval_ast env
             match resolved with

go/src/core/core.go

@@ -235,7 +235,7 @@ func empty_Q(a []MalType) (MalType, error) {
 	case nil:
 		return true, nil
 	default:
-		return nil, errors.New("Count called on non-sequence")
+		return nil, errors.New("empty? called on non-sequence")
 	}
 }
 
@@ -250,7 +250,7 @@ func count(a []MalType) (MalType, error) {
 	case nil:
 		return 0, nil
 	default:
-		return nil, errors.New("Count called on non-sequence")
+		return nil, errors.New("count called on non-sequence")
 	}
 }
 

go/src/step2_eval/step2_eval.go

@@ -79,6 +79,10 @@ func EVAL(ast MalType, env map[string]MalType) (MalType, error) {
 		return eval_ast(ast, env)
 	}
 
+	if len(ast.(List).Val) == 0 {
+		return ast, nil
+	}
+
 	// apply list
 	el, e := eval_ast(ast, env)
 	if e != nil {

groovy/step2_eval.groovy

@@ -32,6 +32,7 @@ eval_ast = { ast, env ->
 
 EVAL = { ast, env ->
     if (! types.list_Q(ast)) return eval_ast(ast, env)
+    if (ast.size() == 0) return ast
 
     def el = eval_ast(ast, env)
     def (f, args) = [el[0], el[1..-1]]

guile/step2_eval.scm

@@ -46,6 +46,7 @@
 
 (define (EVAL ast env)
   (match ast
+    (() ast)
     ((? list?) (eval_func ast env))
     (else (eval_ast ast env))))
 

haskell/step2_eval.hs

@@ -31,6 +31,8 @@ eval_ast ast@(MalHashMap lst m) env = do
 eval_ast ast env = return ast
 
 apply_ast :: MalVal -> (Map.Map String MalVal) -> IOThrows MalVal
+apply_ast ast@(MalList [] _) env = do
+    return ast
 apply_ast ast@(MalList _ _) env = do
     el <- eval_ast ast env
     case el of

haxe/Step2_eval.hx

@@ -37,6 +37,9 @@ class Step2_eval {
         if (!list_Q(ast)) { return eval_ast(ast, env); }
 
         // apply
+        var alst = switch (ast) { case MalList(lst): lst; case _: []; }
+        if (alst.length == 0) { return ast; }
+
         var el = eval_ast(ast, env);
         var lst = switch (el) { case MalList(lst): lst; case _: []; }
         var a0 = lst[0], args = lst.slice(1);

io/step2_eval.io

@@ -21,6 +21,7 @@ eval_ast := method(ast, env,
 
 EVAL := method(ast, env,
     if(ast type != "MalList", return(eval_ast(ast, env)))
+    if(ast isEmpty, return ast)
     el := eval_ast(ast, env)
     f := el at(0)
     args := el rest

js/step2_eval.js

@@ -36,6 +36,9 @@ function _EVAL(ast, env) {
     if (!types._list_Q(ast)) {
         return eval_ast(ast, env);
     }
+    if (ast.length === 0) {
+        return ast;
+    }
 
     // apply list
     var el = eval_ast(ast, env), f = el[0];

julia/step2_eval.jl

@@ -25,6 +25,7 @@ end
 
 function EVAL(ast, env)
     if !isa(ast, Array) return eval_ast(ast, env) end
+    if isempty(ast) return ast end
 
     # apply
     el = eval_ast(ast, env)

kotlin/src/mal/step2_eval.kt

@@ -3,7 +3,7 @@ package mal
 fun read(input: String?): MalType = read_str(input)
 
 fun eval(ast: MalType, env: Map<String, MalType>): MalType =
-        if (ast is MalList) {
+        if (ast is MalList && ast.count() > 0) {
             val evaluated = eval_ast(ast, env) as ISeq
             if (evaluated.first() !is MalFunction) throw MalException("cannot execute non-function")
             (evaluated.first() as MalFunction).apply(evaluated.rest())

lua/step2_eval.lua

@@ -39,6 +39,7 @@ end
 function EVAL(ast, env)
     --print("EVAL: "..printer._pr_str(ast,true))
     if not types._list_Q(ast) then return eval_ast(ast, env) end
+    if #ast == 0 then return ast end
     local args = eval_ast(ast, env)
     local f = table.remove(args, 1)
     return f(unpack(args))

make/step2_eval.mk

@@ -49,7 +49,9 @@ define EVAL
 $(strip $(if $(__ERROR),,\
   $(and $(EVAL_DEBUG),$(info EVAL: $(call _pr_str,$(1))))\
   $(if $(call _list?,$(1)),\
-    $(strip $(call EVAL_INVOKE,$(1),$(2))),\
+    $(if $(call _EQ,0,$(call _count,$(1))),\
+      $(1),\
+      $(strip $(call EVAL_INVOKE,$(1),$(2)))),\
     $(call EVAL_AST,$(1),$(2)))))
 endef
 

mal/step2_eval.mal

@@ -28,10 +28,12 @@
     (eval-ast ast env)
 
     ;; apply list
-    (let* [el (eval-ast ast env)
-          f (first el)
-          args (rest el)]
-      (apply f args))))))
+    (if (empty? ast)
+      ast
+      (let* [el (eval-ast ast env)
+            f (first el)
+            args (rest el)]
+        (apply f args)))))))
 
 
 ;; print

miniMAL/step2_eval.json

@@ -31,10 +31,12 @@
 ["def", "EVAL", ["fn", ["ast", "env"],
   ["if", ["not", ["list?", "ast"]],
         ["eval-ast", "ast", "env"],
-        ["let", ["el", ["eval-ast", "ast", "env"],
-                 "f", ["first", "el"],
-                 "args", ["rest", "el"]],
-          ["apply", "f", "args"]]]]],
+        ["if", ["empty?", "ast"],
+          "ast",
+          ["let", ["el", ["eval-ast", "ast", "env"],
+                   "f", ["first", "el"],
+                   "args", ["rest", "el"]],
+            ["apply", "f", "args"]]]]]],
 
 ["def", "PRINT", ["fn", ["exp"],
   ["pr-str", "exp", true]]],

nim/step2_eval.nim

@@ -24,6 +24,7 @@ proc eval_ast(ast: MalType, env: Table[string, MalType]): MalType =
 proc eval(ast: MalType, env: Table[string, MalType]): MalType =
   case ast.kind
   of List:
+    if ast.list.len == 0: return ast
     let el = ast.eval_ast(env)
     el.list[0].fun(el.list[1 .. ^1])
   else:

perl/step2_eval.pl

@@ -57,6 +57,7 @@ sub EVAL {
     }
 
     # apply list
+    if (scalar(@{$ast->{val}}) == 0) { return $ast; }
     my $el = eval_ast($ast, $env);
     my $f = $el->nth(0);
     return &{ $f }($el->rest());

php/step2_eval.php

@@ -37,6 +37,9 @@ function MAL_EVAL($ast, $env) {
     if (!_list_Q($ast)) {
         return eval_ast($ast, $env);
     }
+    if ($ast->count() === 0) {
+        return $ast;
+    }
 
     // apply list
     $el = eval_ast($ast, $env);

process/guide.md

@@ -515,6 +515,7 @@ repl_env = {'+': lambda a,b: a+b,
 * Modify `EVAL` to check if the first parameter `ast` is a list.
   * `ast` is not a list: then return the result of calling `eval_ast`
     on it.
+  * `ast` is a empty list: return ast unchanged.
   * `ast` is a list: call `eval_ast` to get a new evaluated list. Take
     the first item of the evaluated list and call it as function using
     the rest of the evaluated list as its arguments.

ps/step2_eval.ps

@@ -33,6 +33,7 @@ def EVAL(ast, env):
             return eval_ast(ast, env)
 
         # apply list
+        if len(ast) == 0: return ast
         el = eval_ast(ast, env)
         f = el[0]
         return f(*el[1:])

python/step2_eval.py

@@ -33,6 +33,9 @@ EVAL <- function(ast, env) {
     }
 
     # apply list
+    if (length(ast) == 0) {
+        return(ast)
+    }
     el <- eval_ast(ast, env)
     f <- el[[1]]
     return(do.call(f,el[-1]))

r/step2_eval.r

@@ -21,7 +21,7 @@
     [else ast]))
 
 (define (EVAL ast env)
-  (if (not (list? ast))
+  (if (or (not (list? ast)) (empty? ast))
         (eval-ast ast env)
 
         (let* ([el (eval-ast ast env)]

racket/step2_eval.rkt

@@ -42,6 +42,7 @@ def EVAL(ast, env):
             return eval_ast(ast, env)
 
         # apply list
+        if len(ast) == 0: return ast
         el = eval_ast(ast, env)
         f = el.values[0]
         if isinstance(f, MalFunc):

rpython/step2_eval.py

@@ -33,6 +33,9 @@ def EVAL(ast, env)
     if not ast.is_a? List
         return eval_ast(ast, env)
     end
+    if ast.empty?
+        return ast
+    end
 
     # apply list
     el = eval_ast(ast, env)

ruby/step2_eval.rb

@@ -25,6 +25,8 @@ object step2_eval {
       return eval_ast(ast, env)
 
     // apply list
+    if (ast.asInstanceOf[MalList].value.length == 0)
+      return ast
     eval_ast(ast, env).asInstanceOf[MalList].value match {
       case f :: el => {
         var fn: List[Any] => Any = null

scala/step2_eval.scala

@@ -46,6 +46,10 @@ proc EVAL {ast env} {
     if {![list_q $ast]} {
         return [eval_ast $ast $env]
     }
+    set a0 [lindex [obj_val $ast] 0]
+    if {$a0 == ""} {
+        return $ast
+    }
     set lst_obj [eval_ast $ast $env]
     set lst [obj_val $lst_obj]
     set f [lindex $lst 0]

tcl/step2_eval.tcl

@@ -45,6 +45,9 @@ function EVAL(ast, env)
   if !ListQ(a:ast)
     return EvalAst(a:ast, a:env)
   end
+  if EmptyQ(a:ast)
+    return a:ast
+  endif
 
   " apply list
   let el = EvalAst(a:ast, a:env)