for loops and while statements as expressions

docs/index.md

@@ -195,6 +195,38 @@ single line:
 
     for j = 1,10,3 do print j
 
+A for loop can also be used an expression. The last statement in the body of
+the for loop is coerced into an expression and appended to an accumulating
+table if the value of that expression is not nil.
+
+Doubling every even number:
+
+    doubled_evens = for i=1,20
+      if i % 2 == 0
+        i * 2
+      else
+        i
+
+Filtering out odd numbers:
+    
+    my_numbers = {1,2,3,4,5,6}
+    odds = for x in *my_numbers
+      if x % 2 == 1 then x
+
+For loops at the end of a function body are not accumulated into a table for a
+return value (Instead the function will return `nil`).  Either an explicit
+`return` statement can be used, or the loop can be converted into a list
+comprehension.
+
+    func_a -> for i=1,10 do i
+    func_b -> return for i=1,10 do i
+
+    print func_a! -- prints nil
+    print func_b! -- prints table object
+
+This is done to avoid the needless creation of tables for functions that don't
+need to return the results of the loop.
+
 ## While Loop
 
 The while loop also comes in two variations:
@@ -206,6 +238,10 @@ The while loop also comes in two variations:
 
     while running == true do my_function!
 
+Like for loops, the while loop can also be used an expression. Additionally,
+for a function to return the accumlated value of a while loop, the statement
+must be explicitly returned.
+
 ## Conditionals
 
     have_coins = false

moonscript/compile.lua

@@ -304,7 +304,7 @@ Block_ = (function(_parent_0)
     end,
     ret_stms = function(self, stms, ret)
       if not ret then
-        ret = returner
+        ret = default_return
       end
       local i = 1
       while i < #stms do

moonscript/compile.moon

@@ -205,7 +205,7 @@ class Block_
 
   ret_stms: (stms, ret) =>
     if not ret
-      ret = returner
+      ret = default_return
 
     -- wow I really need a for loop
     i = 1

moonscript/compile/format.lua

@@ -11,8 +11,14 @@ user_error = function(...)
     ...
   })
 end
-returner = function(exp)
-  if ntype(exp) == "chain" and exp[2] == "return" then
+local manual_return = Set({
+  "foreach",
+  "for",
+  "while"
+})
+default_return = function(exp)
+  local t = ntype(exp)
+  if t == "chain" and exp[2] == "return" then
     local items = {
       "explist"
     }
@@ -27,6 +33,8 @@ returner = function(exp)
       "return",
       items
     }
+  elseif manual_return[t] then
+    return exp
   else
     return {
       "return",

moonscript/compile/format.moon

@@ -7,7 +7,7 @@ import itwos from util
 import Set, ntype from data
 import concat, insert from table
 
-export indent_char, returner, moonlib, cascading, non_atomic, has_value, is_non_atomic
+export indent_char, default_return, moonlib, cascading, non_atomic, has_value, is_non_atomic
 export count_lines, is_slice, user_error
 
 indent_char = "  "
@@ -15,12 +15,17 @@ indent_char = "  "
 user_error = (...) ->
   error {"user-error", ...}
 
-returner = (exp) ->
-  if ntype(exp) == "chain" and exp[2] == "return"
+manual_return = Set{"foreach", "for", "while"}
+
+default_return = (exp) ->
+  t = ntype exp
+  if t == "chain" and exp[2] == "return"
     -- extract the return
     items = {"explist"}
     insert items, v for v in *exp[3][2]
     {"return", items}
+  elseif manual_return[t]
+    exp
   else
     {"return", exp}
 

moonscript/compile/line.lua

@@ -35,8 +35,6 @@ line_compile = {
   end,
   assign = function(self, node)
     local _, names, values = unpack(node)
-    local undeclared = self:declare(names)
-    local declare = "local " .. concat(undeclared, ", ")
     if #values == 1 and cascading[ntype(values[1])] then
       return(self:stm({
         "assign",
@@ -44,6 +42,8 @@ line_compile = {
         values[1]
       }))
     end
+    local undeclared = self:declare(names)
+    local declare = "local " .. concat(undeclared, ", ")
     if self:is_stm(values) then
       if #undeclared > 0 then
         self:add(declare)

moonscript/compile/line.moon

@@ -29,13 +29,13 @@ line_compile =
   assign: (node) =>
     _, names, values = unpack node
 
-    undeclared = @declare names
-    declare = "local "..concat(undeclared, ", ")
-
     -- can we extract single cascading value
     if #values == 1 and cascading[ntype values[1]]
       return @stm {"assign", names, values[1]}
 
+    undeclared = @declare names
+    declare = "local "..concat(undeclared, ", ")
+
     if @is_stm values
       @add declare if #undeclared > 0
       if cascading[ntype(values)]

moonscript/compile/value.lua

@@ -5,6 +5,56 @@ local dump = require("moonscript.dump")
 require("moonscript.compile.format")
 local ntype = data.ntype
 local concat, insert = table.concat, table.insert
+local create_accumulate_wrapper
+create_accumulate_wrapper = function(block_pos)
+  return function(self, node)
+    do
+      local _with_0 = self:block("(function()", "end)()")
+      local accum_name = _with_0:init_free_var("accum", {
+        "table"
+      })
+      local value_name = _with_0:free_name("value", true)
+      local inner = node[block_pos]
+      inner[#inner] = {
+        "assign",
+        {
+          value_name
+        },
+        {
+          inner[#inner]
+        }
+      }
+      insert(inner, {
+        "if",
+        {
+          "exp",
+          value_name,
+          "~=",
+          "nil"
+        },
+        {
+          {
+            "chain",
+            "table.insert",
+            {
+              "call",
+              {
+                accum_name,
+                value_name
+              }
+            }
+          }
+        }
+      })
+      _with_0:stm(node)
+      _with_0:stm({
+        "return",
+        accum_name
+      })
+      return _with_0
+    end
+  end
+end
 value_compile = {
   exp = function(self, node)
     local _comp
@@ -60,14 +110,14 @@ value_compile = {
   with = function(self, node)
     do
       local _with_0 = self:block("(function()", "end)()")
-      _with_0:stm(node, returner)
+      _with_0:stm(node, default_return)
       return _with_0
     end
   end,
   ["if"] = function(self, node)
     do
       local _with_0 = self:block("(function()", "end)()")
-      _with_0:stm(node, returner)
+      _with_0:stm(node, default_return)
       return _with_0
     end
   end,
@@ -100,6 +150,9 @@ value_compile = {
       return _with_0
     end
   end,
+  ["for"] = create_accumulate_wrapper(4),
+  foreach = create_accumulate_wrapper(4),
+  ["while"] = create_accumulate_wrapper(3),
   chain = function(self, node)
     local callee = node[2]
     if callee == -1 then

moonscript/compile/value.moon

@@ -12,6 +12,23 @@ import concat, insert from table
 
 export value_compile
 
+create_accumulate_wrapper = (block_pos) ->
+  (node) =>
+    with @block "(function()", "end)()"
+      accum_name = \init_free_var "accum", {"table"}
+      value_name = \free_name "value", true
+
+      inner = node[block_pos]
+      inner[#inner] = {"assign", {value_name}, {inner[#inner]}}
+      insert inner, {
+        "if", {"exp", value_name, "~=", "nil"}, {
+          {"chain", "table.insert", {"call", {accum_name, value_name}}}
+        }
+      }
+
+      \stm node
+      \stm {"return", accum_name}
+
 value_compile =
   exp: (node) =>
     _comp = (i, value) ->
@@ -40,11 +57,11 @@ value_compile =
 
   with: (node) =>
     with @block "(function()", "end)()"
-      \stm node, returner
+      \stm node, default_return
 
   if: (node) =>
     with @block "(function()", "end)()"
-      \stm node, returner
+      \stm node, default_return
 
   comprehension: (node) =>
     exp = node[2]
@@ -58,6 +75,10 @@ value_compile =
       \stm node, action
       \stm {"return", tmp_name}
 
+  for: create_accumulate_wrapper 4
+  foreach: create_accumulate_wrapper 4
+  while: create_accumulate_wrapper 3
+
   chain: (node) =>
     callee = node[2]
 

moonscript/parse.lua

@@ -244,7 +244,7 @@ local build_grammar = wrap(function()
 		Block = Ct(Line * (Break^1 * Line)^0),
 		Line = Cmt(Indent, check_indent) * Statement + _Space * Comment,
 
-		Statement = (Import + While + With + For + Foreach + Return
+		Statement = (Import + While + With + For + ForEach + Return
 			+ ClassDecl + Export + BreakLoop + Ct(ExpList) / flatten_or_mark"explist" * Space) * (
 				-- statement decorators
 				key"if" * Exp * (key"else" * Exp)^-1 * Space / mark"if" +
@@ -277,7 +277,7 @@ local build_grammar = wrap(function()
 		For = key"for" * (Name * sym"=" * Ct(Exp * sym"," * Exp * (sym"," * Exp)^-1)) *
 			key"do"^-1 * Body / mark"for",
 
-		Foreach = key"for" * Ct(NameList) * key"in" * (sym"*" * Exp / mark"unpack" + Exp) * key"do"^-1 * Body / mark"foreach",
+		ForEach = key"for" * Ct(NameList) * key"in" * (sym"*" * Exp / mark"unpack" + Exp) * key"do"^-1 * Body / mark"foreach",
 
 		Comprehension = sym"[" * Exp * CompInner * sym"]" / mark"comprehension",
 
@@ -303,6 +303,7 @@ local build_grammar = wrap(function()
 		SimpleValue =
 			If +
 			With +
+			ForEach + For + While +
 			sym"-" * -SomeSpace * Exp / mark"minus" +
 			sym"#" * Exp / mark"length" +
 			sym"not" * Exp / mark"not" +

tests/inputs/cond.moon

@@ -21,16 +21,6 @@ if cool then wow cool else
 if working
   if cool then if cool then okay else what else nah
 
-while true do print "name"
-
-while 5 + 5
-  print "okay world"
-  working man
-
-while also do
-  i work too
-  "okay"
-
 
 if yeah then no day elseif cool me then okay ya else u way
 if yeah then no dad else if cool you then okay bah else p way

tests/inputs/loops.moon

@@ -28,4 +28,43 @@ x = ->
   for x in y
     y
 
+hello = {1,2,3,4,5}
+
+x = for y in *hello
+  if y % 2 == 0
+    y
+
+x = ->
+  for x in *hello
+    y
+
+t = for i=10,20 do i * 2
+
+hmm = 0
+y = for j = 3,30, 8
+  hmm += 1
+  j * hmm
+
+->
+  for k=10,40
+    "okay"
+
+->
+  return for k=10,40
+    "okay"
+
+while true do print "name"
+
+while 5 + 5
+  print "okay world"
+  working man
+
+while also do
+  i work too
+  "okay"
+
+i = 0
+x = while i < 10
+  i += 1
+
 

tests/inputs/syntax.moon

@@ -160,6 +160,8 @@ what whack - 5
 
 x = hello - world - something
 
-
+((something = with what
+  \cool 100) ->
+  print something)!
 
 

tests/inputs/with.moon

@@ -20,3 +20,14 @@ with leaf
 
 zyzyzy = with something
   .set_state "hello world"
+
+
+x = 5 + with Something!
+  \write "hello world"
+
+
+x = {
+  hello: with yeah
+    \okay!
+}
+

tests/outputs/cond.lua

@@ -37,17 +37,6 @@ if working then
     local _ = nah
   end
 end
-while true do
-  print("name")
-end
-while 5 + 5 do
-  print("okay world")
-  working(man)
-end
-while also do
-  i(work(too))
-  local _ = "okay"
-end
 if yeah then
   no(day)
 elseif cool(me) then

tests/outputs/loops.lua

@@ -37,3 +37,99 @@ x = function()
     local _ = y
   end
 end
+local hello = {
+  1,
+  2,
+  3,
+  4,
+  5
+}
+x = (function()
+  local _accum_0 = { }
+  do
+    local _item_0 = hello
+    for _index_0 = 1, #_item_0 do
+      local y = _item_0[_index_0]
+      local _value_0
+      if y % 2 == 0 then
+        _value_0 = y
+      end
+      if _value_0 ~= nil then
+        table.insert(_accum_0, _value_0)
+      end
+    end
+  end
+  return _accum_0
+end)()
+x = function()
+  do
+    local _item_0 = hello
+    for _index_0 = 1, #_item_0 do
+      local x = _item_0[_index_0]
+      local _ = y
+    end
+  end
+end
+local t = (function()
+  local _accum_0 = { }
+  for i = 10, 20 do
+    local _value_0 = i * 2
+    if _value_0 ~= nil then
+      table.insert(_accum_0, _value_0)
+    end
+  end
+  return _accum_0
+end)()
+local hmm = 0
+local y = (function()
+  local _accum_0 = { }
+  for j = 3, 30, 8 do
+    hmm = hmm + 1
+    local _value_0 = j * hmm
+    if _value_0 ~= nil then
+      table.insert(_accum_0, _value_0)
+    end
+  end
+  return _accum_0
+end)()
+local _
+_ = function()
+  for k = 10, 40 do
+    _ = "okay"
+  end
+end
+_ = function()
+  return (function()
+    local _accum_0 = { }
+    for k = 10, 40 do
+      local _value_0 = "okay"
+      if _value_0 ~= nil then
+        table.insert(_accum_0, _value_0)
+      end
+    end
+    return _accum_0
+  end)()
+end
+while true do
+  print("name")
+end
+while 5 + 5 do
+  print("okay world")
+  working(man)
+end
+while also do
+  i(work(too))
+  _ = "okay"
+end
+local i = 0
+x = (function()
+  local _accum_0 = { }
+  while i < 10 do
+    i = i + 1
+    local _value_0 = i
+    if _value_0 ~= nil then
+      table.insert(_accum_0, _value_0)
+    end
+  end
+  return _accum_0
+end)()

tests/outputs/syntax.lua

@@ -165,3 +165,13 @@ what(whack + 5)
 _ = 5 - what(wack)
 what(whack - 5)
 x = hello - world - something
+(function(something)
+  if something == nil then
+    do
+      local _with_0 = what
+      _with_0:cool(100)
+      something = _with_0
+    end
+  end
+  return print(something)
+end)()

tests/outputs/with.lua

@@ -24,3 +24,19 @@ do
   _with_0.set_state("hello world")
   zyzyzy = _with_0
 end
+local x = 5 + (function()
+  do
+    local _with_0 = Something()
+    _with_0:write("hello world")
+    return _with_0
+  end
+end)()
+x = {
+  hello = (function()
+    do
+      local _with_0 = yeah
+      _with_0:okay()
+      return _with_0
+    end
+  end)()
+}

todo

@@ -1,10 +1,8 @@
 # TODO
 
-- use `with` as an arugment to function (normal expression)
 - varargs that get put in a nested generated function aren't valid anymore:
 
 - cascading expressions in function
-- assigning a for loop
 
 - class expressions, x = class extends Hello do new: => print "hello"