Initial working version.

17 files changed, 909 insertions, 173 deletions

diff --git a/Makefile b/Makefile
index 3b96414..388f411 100644
--- a/Makefile
+++ b/Makefile
@@ -11,9 +11,11 @@ UNINSTALL_VERSION=
 # ========= You shouldn't need to mess with any of these variables below ================
 
 MOON_FILES= code_obj.moon error_handling.moon files.moon nomsu.moon nomsu_compiler.moon \
-			syntax_tree.moon parser.moon containers.moon bitops.moon
+			syntax_tree.moon parser.moon containers.moon bitops.moon \
+			parser2.moon pretty_errors.moon string2.moon
 LUA_FILES= code_obj.lua consolecolors.lua error_handling.lua files.lua nomsu.lua nomsu_compiler.lua \
-		   syntax_tree.lua parser.lua containers.lua bitops.lua utils.lua
+		   syntax_tree.lua parser.lua containers.lua bitops.lua utils.lua \
+		   parser2.lua pretty_errors.lua string2.lua
 CORE_NOM_FILES= $(wildcard core/*.nom)
 CORE_LUA_FILES= $(patsubst %.nom,%.lua,$(CORE_NOM_FILES))
 LIB_NOM_FILES= $(wildcard lib/*.nom)
diff --git a/containers.lua b/containers.lua
index 865098d..1b3fd94 100644
--- a/containers.lua
+++ b/containers.lua
@@ -264,83 +264,69 @@ for i, entry in ipairs(Dict({
 })) do
   assert(i == 1 and entry.key == "x" and entry.value == 99, "ipairs compatibility issue")
 end
-local Text
 do
   local reverse, upper, lower, find, byte, match, gmatch, gsub, sub, format, rep
   do
     local _obj_0 = string
     reverse, upper, lower, find, byte, match, gmatch, gsub, sub, format, rep = _obj_0.reverse, _obj_0.upper, _obj_0.lower, _obj_0.find, _obj_0.byte, _obj_0.match, _obj_0.gmatch, _obj_0.gsub, _obj_0.sub, _obj_0.format, _obj_0.rep
   end
-  local as_lua_id
-  as_lua_id = function(str)
-    str = gsub(str, "^\3*$", "%1\3")
-    str = gsub(str, "x([0-9A-F][0-9A-F])", "x78%1")
-    str = gsub(str, "%W", function(c)
-      if c == ' ' then
-        return '_'
-      else
-        return format("x%02X", byte(c))
-      end
-    end)
-    str = gsub(str, "^_*%d", "_%1")
-    return str
-  end
-  local line_matcher = re.compile([[ 
-        lines <- {| line (%nl line)* |}
-        line <- {(!%nl .)*}
-    ]], {
-    nl = lpeg.P("\r") ^ -1 * lpeg.P("\n")
-  })
+  local string2 = require('string2')
+  local lines, line, line_at, as_lua_id
+  lines, line, line_at, as_lua_id = string2.lines, string2.line, string2.line_at, string2.as_lua_id
   local text_methods = {
-    reversed = function(self)
-      return reverse(tostring(self))
-    end,
-    uppercase = function(self)
-      return upper(tostring(self))
-    end,
-    lowercase = function(self)
-      return lower(tostring(self))
-    end,
-    as_lua_id = function(self)
-      return as_lua_id(tostring(self))
-    end,
-    formatted_with_1 = function(self, args)
-      return format(tostring(self), unpack(args))
-    end,
-    byte_1 = function(self, i)
-      return byte(tostring(self), i)
-    end,
-    position_of_1 = function(self)
-      return find(tostring(self))
-    end,
-    position_of_1_after_2 = function(self, i)
-      return find(tostring(self), i)
-    end,
+    formatted_with_1 = format,
+    byte_1 = byte,
+    position_of_1 = find,
+    position_of_1_after_2 = find,
     bytes_1_to_2 = function(self, start, stop)
       return List({
         byte(tostring(self), start, stop)
       })
     end,
+    [as_lua_id("with 1 -> 2")] = gsub,
     bytes = function(self)
       return List({
-        byte(tostring(self), 1, #self)
+        byte(tostring(self), 1, -1)
       })
     end,
-    capitalized = function(self)
-      return gsub(tostring(self), '%l', upper, 1)
-    end,
     lines = function(self)
-      return List(line_matcher:match(self))
+      return List(lines(self))
+    end,
+    line_1 = line,
+    wrap_to_1 = function(self, maxlen)
+      local _lines = { }
+      local _list_0 = self:lines()
+      for _index_0 = 1, #_list_0 do
+        local line = _list_0[_index_0]
+        while #line > maxlen do
+          local chunk = line:sub(1, maxlen)
+          local split = chunk:find(' ', maxlen - 8) or maxlen
+          chunk = line:sub(1, split)
+          line = line:sub(split + 1, -1)
+          _lines[#_lines + 1] = chunk
+        end
+        _lines[#_lines + 1] = line
+      end
+      return table.concat(_lines, "\n")
+    end,
+    line_at_1 = function(self, i)
+      return (line_at(self, i))
+    end,
+    line_number_of_1 = function(self, i)
+      return select(2, line_at(self, i))
+    end,
+    line_position_of_1 = function(self, i)
+      return select(3, line_at(self, i))
     end,
     matches_1 = function(self, patt)
-      return match(tostring(self), patt) and true or false
+      return match(self, patt) and true or false
     end,
     [as_lua_id("* 1")] = function(self, n)
       return rep(self, n)
     end,
     matching_1 = function(self, patt)
       local result = { }
-      local stepper, x, i = gmatch(tostring(self), patt)
+      local stepper, x, i = gmatch(self, patt)
       while true do
         local tmp = List({
           stepper(x, i)
@@ -352,23 +338,10 @@ do
         result[#result + 1] = tmp
       end
       return List(result)
-    end,
-    [as_lua_id("with 1 -> 2")] = function(self, patt, sub)
-      return gsub(tostring(self), patt, sub)
-    end,
-    _coalesce = function(self)
-      if rawlen(self) > 1 then
-        local s = table.concat(self)
-        for i = rawlen(self), 2, -1 do
-          self[i] = nil
-        end
-        self[1] = s
-      end
-      return self
     end
   }
   setmetatable(text_methods, {
-    __index = string
+    __index = string2
   })
   getmetatable("").__index = function(self, i)
     if type(i) == 'number' then
@@ -382,6 +355,5 @@ do
 end
 return {
   List = List,
-  Dict = Dict,
-  Text = Text
+  Dict = Dict
 }
diff --git a/containers.moon b/containers.moon
index 243e129..eaf007a 100644
--- a/containers.moon
+++ b/containers.moon
@@ -106,68 +106,45 @@ Dict = (t)-> setmetatable(t, _dict_mt)
 for i,entry in ipairs(Dict({x:99}))
     assert(i == 1 and entry.key == "x" and entry.value == 99, "ipairs compatibility issue")
 
-local Text
 do
     {:reverse, :upper, :lower, :find, :byte, :match, :gmatch, :gsub, :sub, :format, :rep} = string
-
-    -- Convert an arbitrary text into a valid Lua identifier. This function is injective,
-    -- but not idempotent, i.e. if (x != y) then (as_lua_id(x) != as_lua_id(y)),
-    -- but as_lua_id(x) is not necessarily equal to as_lua_id(as_lua_id(x))
-    as_lua_id = (str)->
-        -- Empty strings are not valid lua identifiers, so treat them like "\3",
-        -- and treat "\3" as "\3\3", etc. to preserve injectivity.
-        str = gsub str, "^\3*$", "%1\3"
-        -- Escape 'x' when it precedes something that looks like an uppercase hex sequence.
-        -- This way, all Lua IDs can be unambiguously reverse-engineered, but normal usage
-        -- of 'x' won't produce ugly Lua IDs.
-        -- i.e. "x" -> "x", "oxen" -> "oxen", but "Hex2Dec" -> "Hex782Dec" and "He-ec" -> "Hex2Dec"
-        str = gsub str, "x([0-9A-F][0-9A-F])", "x78%1"
-        -- Map spaces to underscores, and everything else non-alphanumeric to hex escape sequences
-        str = gsub str, "%W", (c)->
-            if c == ' ' then '_'
-            else format("x%02X", byte(c))
-        -- Lua IDs can't start with numbers, so map "1" -> "_1", "_1" -> "__1", etc.
-        str = gsub str, "^_*%d", "_%1"
-        return str
-
-    line_matcher = re.compile([[ 
-        lines <- {| line (%nl line)* |}
-        line <- {(!%nl .)*}
-    ]], nl:lpeg.P("\r")^-1 * lpeg.P("\n"))
-
+    string2 = require 'string2'
+    {:lines, :line, :line_at, :as_lua_id} = string2
     text_methods =
-        reversed:=>reverse(tostring @)
-        uppercase:=>upper(tostring @)
-        lowercase:=>lower(tostring @)
-        as_lua_id:=>as_lua_id(tostring @)
-        formatted_with_1:(args)=>format(tostring(@), unpack(args))
-        byte_1:(i)=>byte(tostring(@), i)
-        position_of_1:=>find(tostring @),
-        position_of_1_after_2:(i)=> find(tostring(@), i)
+        formatted_with_1:format, byte_1:byte, position_of_1:find, position_of_1_after_2:find,
         bytes_1_to_2: (start, stop)=> List{byte(tostring(@), start, stop)}
-        bytes: => List{byte(tostring(@), 1, #@)},
-        capitalized: => gsub(tostring(@), '%l', upper, 1)
-        lines: => List(line_matcher\match(@))
-        matches_1: (patt)=> match(tostring(@), patt) and true or false
+        [as_lua_id "with 1 -> 2"]: gsub
+        bytes: => List{byte(tostring(@), 1, -1)},
+        lines: => List(lines(@))
+        line_1: line
+        wrap_to_1: (maxlen)=>
+            _lines = {}
+            for line in *@lines!
+                while #line > maxlen
+                    chunk = line\sub(1, maxlen)
+                    split = chunk\find(' ', maxlen-8) or maxlen
+                    chunk = line\sub(1, split)
+                    line = line\sub(split+1, -1)
+                    _lines[#_lines+1] = chunk
+                _lines[#_lines+1] = line
+            return table.concat(_lines, "\n")
+                                
+        line_at_1: (i)=> (line_at(@, i))
+        line_number_of_1: (i)=> select(2, line_at(@, i))
+        line_position_of_1: (i)=> select(3, line_at(@, i))
+        matches_1: (patt)=> match(@, patt) and true or false
         [as_lua_id "* 1"]: (n)=> rep(@, n)
         matching_1: (patt)=>
             result = {}
-            stepper,x,i = gmatch(tostring(@), patt)
+            stepper,x,i = gmatch(@, patt)
             while true
                 tmp = List{stepper(x,i)}
                 break if #tmp == 0
                 i = tmp[1]
                 result[#result+1] = tmp
             return List(result)
-        [as_lua_id "with 1 -> 2"]: (patt, sub)=> gsub(tostring(@), patt, sub)
-        _coalesce: =>
-            if rawlen(@) > 1
-                s = table.concat(@)
-                for i=rawlen(@), 2, -1 do @[i] = nil
-                @[1] = s
-            return @
     
-    setmetatable(text_methods, {__index:string})
+    setmetatable(text_methods, {__index:string2})
 
     getmetatable("").__index = (i)=>
         -- Use [] for accessing text characters, or s[{3,4}] for s:sub(3,4)
@@ -175,4 +152,4 @@ do
         elseif type(i) == 'table' then return sub(@, i[1], i[2])
         else return text_methods[i]
 
-return {:List, :Dict, :Text}
+return {:List, :Dict}
diff --git a/nomsu.4.peg b/nomsu.4.peg
new file mode 100644
index 0000000..ed119c5
--- /dev/null
+++ b/nomsu.4.peg
@@ -0,0 +1,208 @@
+-- Nomsu version 4
+file:
+    {:curr_indent: ' '* :}
+    (((action / expression / inline_block / indented_block) eol !.)
+     / file_chunks / empty_block)
+    {:curr_indent: %nil :}
+    !.
+
+shebang: "#!" (!"nomsu" [^%nl])* "nomsu" ws+ "-V" ws* {:version: [0-9.]+ :} [^%nl]*
+
+file_chunks (FileChunks):
+    {:curr_indent: ' '* :}
+    shebang? comment? blank_lines?
+    (top_block (section_division nl_nodent top_block)*)
+    blank_lines?
+    ws* unexpected_chunk?
+    {:curr_indent: %nil :}
+
+top_block (Block):
+    {:curr_indent: ' '* :}
+    comment? blank_lines? statement (nl_nodent statement?)*
+    {:curr_indent: %nil :}
+
+empty_block (Block):
+    {:curr_indent: ' '* :}
+    comment? blank_lines?
+    {:curr_indent: %nil :}
+
+nodent: (unexpected_indent [^%nl]* / =curr_indent)
+indent: =curr_indent ("    ")
+blank_lines: %nl ((nodent comment / ws*) %nl)*
+eol: ws* eol_comment? (!. / &%nl)
+
+nl_nodent: blank_lines nodent
+nl_indent: blank_lines {:curr_indent: indent :} (comment nl_nodent)*
+
+comment (Comment):
+    "#" {~ [^%nl]* (%nl+ (indent -> '') [^%nl]*)* ~}
+eol_comment (Comment):
+    "#" {[^%nl]*}
+
+unexpected_code: ws* _unexpected_code
+_unexpected_code (Error):
+    {:error: {~ [^%nl]+ -> "Couldn't parse this code" ~} :}
+unexpected_chunk (Error):
+    {:error: {~ .+ -> "Couldn't parse this code" ~} :}
+unexpected_indent (Error):
+    {:error: {~ (=curr_indent ws+) -> "Messed up indentation" ~} :}
+    {:hint: {~ '' -> 'Either make sure this line is aligned with the one above it, or make sure the previous line ends with something that uses indentation, like ":" or "(..)"' ~} :}
+missing_paren_err (Error):
+    {:error: {~ eol -> 'Line ended without finding a closing )-parenthesis' ~} :}
+    {:hint: {~ '' -> 'Put a ")" here' ~} :}
+missing_quote_err (Error):
+    {:error: {~ eol -> 'Line ended before finding a closing double quotation mark' ~} :}
+    {:hint: {~ "" -> "Put a quotation mark here" ~} :}
+missing_bracket_error (Error):
+    {:error: {~ eol -> "Line ended before finding a closing ]-bracket" ~} :}
+    {:hint: {~ '' -> 'Put a "]" here' ~} :}
+missing_brace_error (Error):
+    {:error: {~ eol -> "Line ended before finding a closing }-brace" ~} :}
+    {:hint: {~ '' -> 'Put a "}" here' ~} :}
+
+section_division: ("~")^+3 eol
+
+inline_block:
+    "(" ws* inline_block  ws* ")" / raw_inline_block
+raw_inline_block (Block):
+    (!"::") ":" ws* ((inline_statement (ws* ";" ws* inline_statement)*) / !(eol nl_indent))
+indented_block (Block):
+    ":" eol nl_indent statement (nl_nodent statement?)*
+    (%nl (ws* %nl)* nodent (comment / eol / unexpected_code))*
+    {:curr_indent: %nil :}
+
+statement:
+    (action / expression) (eol / unexpected_code)
+
+inline_statement: (inline_action / inline_expression)
+
+noindex_inline_expression:
+    number / variable / inline_text / inline_list / inline_dict / inline_nomsu
+    / ( "("
+            ws* (inline_action / inline_expression) ws*
+            (ws* ',' ws* (inline_action / inline_expression) ws*)*
+        (")" / missing_paren_err / unexpected_code)
+      )
+inline_expression: index_chain / noindex_inline_expression 
+indented_expression:
+    cool_indented_text / indented_text / indented_nomsu / indented_list / indented_dict / ({|
+        "(..)" nl_indent
+            (action / expression) (eol / unexpected_code)
+            (%nl (ws* %nl)* nodent (comment / eol / unexpected_code))*
+        {:curr_indent: %nil :}
+    |} -> unpack)
+expression:
+    inline_expression / indented_expression
+
+inline_nomsu (EscapedNomsu): "\" (inline_expression / inline_block)
+indented_nomsu (EscapedNomsu):
+    "\" (noindex_inline_expression / inline_block / indented_expression / indented_block)
+
+index_chain (IndexChain):
+    noindex_inline_expression ("." (text_word / noindex_inline_expression))+
+
+-- Actions need either at least 1 word, or at least 2 tokens
+inline_action (Action):
+    !section_division
+    ({:target: inline_arg :} ws* "::" ws*)?
+    (   (inline_arg (ws* (inline_arg / word))+)
+      / (word       (ws* (inline_arg / word))*))
+    (ws* inline_block)?
+inline_arg: inline_expression / inline_block
+action (Action):
+    !section_division
+    ({:target: arg :} (nl_nodent "..")? ws* "::" (nl_nodent "..")? ws*)?
+    (  (arg  ((nl_nodent "..")? ws* (arg / word))+)
+     / (word ((nl_nodent "..")? ws* (arg / word))*))
+arg: expression / inline_block / indented_block
+
+word: !number { operator_char+ / ident_char+ }
+
+text_word (Text): word
+
+inline_text (Text):
+    !(cool_indented_text / indented_text)
+    ('"' _inline_text* ('"' / missing_quote_err / unexpected_code))
+_inline_text:
+    {~ (('\"' -> '"') / ('\\' -> '\') / escaped_char / [^%nl\"])+ ~}
+    / inline_text_interpolation
+inline_text_interpolation:
+    "\" (
+        variable / inline_list / inline_dict / inline_text
+        / ("("
+            ws* (inline_action / inline_expression) ws*
+            (ws* ',' ws* (inline_action / inline_expression) ws*)*
+        (")" / missing_paren_err / unexpected_code))
+    )
+
+indented_text (Text):
+    '".."' eol %nl {%nl+}? {:curr_indent: indent :}
+        (indented_plain_text / text_interpolation / {~ %nl+ (=curr_indent -> "") ~})*
+    unexpected_code?
+    {:curr_indent: %nil :}
+cool_indented_text (Text):
+    ({|
+        '"' _inline_text* '\' %nl {:curr_indent: indent :} '..'
+            (indented_plain_text / text_interpolation / {~ %nl+ (=curr_indent -> "") ~})*
+        unexpected_code?
+    |} -> unpack)
+    ({(%nl &%nl)+}? %nl =curr_indent '..' _inline_text* '"')?
+-- Tracking text-lines-within-indented-text as separate objects allows for better debugging line info
+indented_plain_text (Text):
+    {~ (("\\" -> "\") / (("\" blank_lines =curr_indent "..") -> "") / (!text_interpolation "\") / [^%nl\]+)+
+        (%nl+ (=curr_indent -> ""))* ~}
+text_interpolation:
+    inline_text_interpolation / ("\" indented_expression (blank_lines =curr_indent "..")?)
+
+number (Number): (("-"? (([0-9]+ "." [0-9]+) / ("." [0-9]+) / "0x" [0-9a-fA-F]+ / ([0-9]+)))-> tonumber)
+
+-- Variables can be nameless (i.e. just %) and can only contain identifier chars.
+-- This ensures you don't get weird parsings of `%x+%y` or `%'s thing`.
+variable (Var): "%" {ident_char*}
+
+inline_list (List):
+    !('[..]')
+    "[" ws*
+        (inline_list_item (ws* ',' ws* inline_list_item)* (ws* ',')?)? ws*
+    ("]" / (","? (missing_bracket_error / unexpected_code)))
+indented_list (List):
+    "[..]" eol nl_indent
+        list_line (nl_nodent list_line?)*
+        (%nl (ws* %nl)* nodent (comment / eol / unexpected_code))*
+    (","? unexpected_code)?
+list_line:
+      (inline_list_item ws* "," ws*)+ eol
+    / (inline_list_item ws* "," ws*)* (action / expression) eol
+inline_list_item: inline_action / inline_expression
+
+inline_dict (Dict):
+    !('{..}')
+    "{" ws*
+        (inline_dict_entry (ws* ',' ws* inline_dict_entry)*)? ws*
+    ("}" / (","? (missing_brace_error / unexpected_code)))
+indented_dict (Dict):
+    "{..}" eol nl_indent
+        dict_line (nl_nodent dict_line?)*
+        (%nl (ws* %nl)* nodent (comment / eol / unexpected_code))*
+    (","? unexpected_code)?
+dict_line:
+      (inline_dict_entry ws* "," ws*)+ eol
+    / (inline_dict_entry ws* "," ws*)* dict_entry eol
+dict_entry(DictEntry):
+    dict_key (ws* ":" ws* (action / expression))?
+inline_dict_entry(DictEntry):
+    dict_key (ws* ":" ws* (inline_action / inline_expression)?)?
+dict_key:
+    text_word / inline_expression
+
+operator_char: ['`~!@$^&*+=|<>?/-]
+ident_char: [a-zA-Z0-9_] / %utf8_char
+ws: [ %tab]
+
+escaped_char:
+    ("\"->'') (
+        (([xX]->'') ((({[0-9a-fA-F]^2} %number_16) -> tonumber) -> tochar))
+      / ((([0-9] [0-9]^-2) -> tonumber) -> tochar)
+      / ("a"->ascii_7)  / ("b"->ascii_8)  / ("t"->ascii_9)  / ("n"->ascii_10)
+      / ("v"->ascii_11) / ("f"->ascii_12) / ("r"->ascii_13)
+    )
diff --git a/nomsu.lua b/nomsu.lua
index 24ca589..0a0dce1 100644
--- a/nomsu.lua
+++ b/nomsu.lua
@@ -59,7 +59,7 @@ else
 end
 local usage = [=[Nomsu Compiler
 
-Usage: (nomsu | lua nomsu.lua | moon nomsu.moon) [-V version] [-O optimization level] [-v] [-c] [-s] [-t] [-I file] [--help | -h] [--version] [--no-core] [file [nomsu args...]]
+Usage: (nomsu | lua nomsu.lua | moon nomsu.moon) [-V version] [-O optimization level] [-v] [-c] [-s] [-I file] [--help | -h] [--version] [--no-core] [file [nomsu args...]]
 
 OPTIONS
     -O <level> Run the compiler with the given optimization level (>0: use precompiled .lua versions of Nomsu files, when available).
@@ -98,29 +98,24 @@ if not arg or debug.getinfo(2).func == require then
 end
 local file_queue = { }
 local sep = "\3"
-local parser = re.compile([[    args <- {| (flag %sep)* (({~ file ~} -> add_file) {:primary_file: '' -> true :} %sep)?
+local parser = re.compile([[    args <- {| (flag %sep)* (({~ file ~} -> add_file) {:primary_file: %true :} %sep)?
         {:nomsu_args: {| ({(!%sep .)*} %sep)* |} :} %sep? |} !.
     flag <-
-        {:optimization: "-O" (%sep? (([0-9]+) -> tonumber))? :}
+        {:optimization: "-O" (%sep? %number)? :}
       / ("-I" %sep? ({~ file ~} -> add_file))
-      / ("-e" %sep? (({} {~ file ~}) -> add_exec_string) {:exec_strings: '' -> true :})
-      / ({:check_syntax: ("-s" -> true):})
-      / ({:compile: ("-c" -> true):})
-      / ({:compile: ("-c" -> true):})
-      / {:verbose: ("-v" -> true) :}
-      / {:help: (("-h" / "--help") -> true) :}
-      / {:version: ("--version" -> true) :}
-      / {:no_core: ("--no-core" -> true) :}
+      / ("-e" %sep? (({} {~ file ~}) -> add_exec_string) {:exec_strings: %true :})
+      / ({:check_syntax: "-s" %true:})
+      / ({:compile: "-c" %true:})
+      / {:verbose: "-v" %true :}
+      / {:help: ("-h" / "--help") %true :}
+      / {:version: "--version" %true :}
+      / {:no_core: "--no-core" %true :}
       / {:debugger: ("-d" %sep? {(!%sep .)*}) :}
       / {:requested_version: "-V" (%sep? {([0-9.])+})? :}
     file <- ("-" -> "stdin") / {(!%sep .)+}
 ]], {
-  ["true"] = (function()
-    return true
-  end),
-  tonumber = (function(self)
-    return tonumber(self)
-  end),
+  ["true"] = lpeg.Cc(true),
+  number = lpeg.R("09") ^ 1 / tonumber,
   sep = lpeg.P(sep),
   add_file = function(f)
     return table.insert(file_queue, f)
@@ -255,7 +250,7 @@ run = function()
             _continue_0 = true
             break
           end
-          nomsu:parse(file, source)
+          local tree = nomsu:parse(file, source)
           print("Parse succeeded: " .. tostring(filename))
         end
         if args.compile then
diff --git a/nomsu.moon b/nomsu.moon
index 7a8ff34..0c989e6 100755
--- a/nomsu.moon
+++ b/nomsu.moon
@@ -20,7 +20,7 @@ else
 usage = [=[
 Nomsu Compiler
 
-Usage: (nomsu | lua nomsu.lua | moon nomsu.moon) [-V version] [-O optimization level] [-v] [-c] [-s] [-t] [-I file] [--help | -h] [--version] [--no-core] [file [nomsu args...]]
+Usage: (nomsu | lua nomsu.lua | moon nomsu.moon) [-V version] [-O optimization level] [-v] [-c] [-s] [-I file] [--help | -h] [--version] [--no-core] [file [nomsu args...]]
 
 OPTIONS
     -O <level> Run the compiler with the given optimization level (>0: use precompiled .lua versions of Nomsu files, when available).
@@ -57,24 +57,23 @@ if not arg or debug.getinfo(2).func == require
 file_queue = {}
 sep = "\3"
 parser = re.compile([[
-    args <- {| (flag %sep)* (({~ file ~} -> add_file) {:primary_file: '' -> true :} %sep)?
+    args <- {| (flag %sep)* (({~ file ~} -> add_file) {:primary_file: %true :} %sep)?
         {:nomsu_args: {| ({(!%sep .)*} %sep)* |} :} %sep? |} !.
     flag <-
-        {:optimization: "-O" (%sep? (([0-9]+) -> tonumber))? :}
+        {:optimization: "-O" (%sep? %number)? :}
       / ("-I" %sep? ({~ file ~} -> add_file))
-      / ("-e" %sep? (({} {~ file ~}) -> add_exec_string) {:exec_strings: '' -> true :})
-      / ({:check_syntax: ("-s" -> true):})
-      / ({:compile: ("-c" -> true):})
-      / ({:compile: ("-c" -> true):})
-      / {:verbose: ("-v" -> true) :}
-      / {:help: (("-h" / "--help") -> true) :}
-      / {:version: ("--version" -> true) :}
-      / {:no_core: ("--no-core" -> true) :}
+      / ("-e" %sep? (({} {~ file ~}) -> add_exec_string) {:exec_strings: %true :})
+      / ({:check_syntax: "-s" %true:})
+      / ({:compile: "-c" %true:})
+      / {:verbose: "-v" %true :}
+      / {:help: ("-h" / "--help") %true :}
+      / {:version: "--version" %true :}
+      / {:no_core: "--no-core" %true :}
       / {:debugger: ("-d" %sep? {(!%sep .)*}) :}
       / {:requested_version: "-V" (%sep? {([0-9.])+})? :}
     file <- ("-" -> "stdin") / {(!%sep .)+}
 ]], {
-    true:(-> true), tonumber:(=>tonumber(@)), sep:lpeg.P(sep)
+    true:lpeg.Cc(true), number:lpeg.R("09")^1/tonumber, sep:lpeg.P(sep)
     add_file: (f)-> table.insert(file_queue, f)
     add_exec_string: (pos, s)->
         name = "command line arg @#{pos}.nom"
@@ -165,7 +164,7 @@ run = ->
                 -- Check syntax
                 file, source = get_file_and_source(filename)
                 continue unless file
-                nomsu\parse(file, source)
+                tree = nomsu\parse(file, source)
                 print("Parse succeeded: #{filename}")
 
             if args.compile
diff --git a/nomsu_compiler.lua b/nomsu_compiler.lua
index e6462b6..510de16 100644
--- a/nomsu_compiler.lua
+++ b/nomsu_compiler.lua
@@ -35,6 +35,7 @@ do
 end
 local AST = require("syntax_tree")
 local Parser = require("parser")
+local make_parser = require("parser2")
 SOURCE_MAP = { }
 table.map = function(t, fn)
   return setmetatable((function()
@@ -61,6 +62,69 @@ table.copy = function(t)
     return _tbl_0
   end)(), getmetatable(t))
 end
+local Parsers = { }
+local max_parser_version = 0
+for version = 1, 999 do
+  local _continue_0 = false
+  repeat
+    if not (version == 4) then
+      _continue_0 = true
+      break
+    end
+    local peg_file = io.open("nomsu." .. tostring(version) .. ".peg")
+    if not peg_file and package.nomsupath then
+      for path in package.nomsupath:gmatch("[^;]+") do
+        peg_file = io.open(path .. "/nomsu." .. tostring(version) .. ".peg")
+        if peg_file then
+          break
+        end
+      end
+    end
+    if not (peg_file) then
+      break
+    end
+    max_parser_version = version
+    local make_tree
+    make_tree = function(tree, userdata)
+      local cls = AST[tree.type]
+      tree.source = Source(userdata.filename, tree.start, tree.stop)
+      tree.start, tree.stop = nil, nil
+      tree.type = nil
+      do
+        local _accum_0 = { }
+        local _len_0 = 1
+        for _index_0 = 1, #tree do
+          local t = tree[_index_0]
+          if AST.is_syntax_tree(t, "Comment") then
+            _accum_0[_len_0] = t
+            _len_0 = _len_0 + 1
+          end
+        end
+        tree.comments = _accum_0
+      end
+      if #tree.comments == 0 then
+        tree.comments = nil
+      end
+      for i = #tree, 1, -1 do
+        if AST.is_syntax_tree(tree[i], "Comment") then
+          table.remove(tree, i)
+        end
+      end
+      tree = setmetatable(tree, cls)
+      cls.source_code_for_tree[tree] = userdata.source
+      if tree.__init then
+        tree:__init()
+      end
+      return tree
+    end
+    Parsers[version] = make_parser(peg_file:read("*a"), make_tree)
+    peg_file:close()
+    _continue_0 = true
+  until true
+  if not _continue_0 then
+    break
+  end
+end
 local MAX_LINE = 80
 local NomsuCompiler = setmetatable({
   name = "Nomsu"
@@ -79,12 +143,68 @@ local NomsuCompiler = setmetatable({
     return self.name
   end
 })
+local _anon_chunk = 0
 do
   NomsuCompiler.NOMSU_COMPILER_VERSION = 7
-  NomsuCompiler.NOMSU_SYNTAX_VERSION = Parser.version
+  NomsuCompiler.NOMSU_SYNTAX_VERSION = max_parser_version
   NomsuCompiler.nomsu = NomsuCompiler
-  NomsuCompiler.parse = function(self, ...)
-    return Parser.parse(...)
+  NomsuCompiler.parse = function(self, nomsu_code, source, version)
+    if source == nil then
+      source = nil
+    end
+    if version == nil then
+      version = nil
+    end
+    source = source or nomsu_code.source
+    nomsu_code = tostring(nomsu_code)
+    if not (source) then
+      source = Source("anonymous chunk #" .. tostring(_anon_chunk), 1, #nomsu_code)
+      _anon_chunk = _anon_chunk + 1
+    end
+    version = version or nomsu_code:match("^#![^\n]*nomsu[ ]+-V[ ]*([0-9.]+)")
+    local syntax_version = version and tonumber(version:match("^[0-9]+")) or max_parser_version
+    local parse = Parsers[syntax_version] or Parsers[max_parser_version]
+    local tree = parse(nomsu_code, source.filename)
+    local pretty_error = require("pretty_errors")
+    local find_errors
+    find_errors = function(t)
+      if t.type == "Error" then
+        return pretty_error({
+          error = t.error,
+          hint = t.hint,
+          source = t:get_source_code(),
+          start = t.source.start,
+          stop = t.source.stop
+        })
+      end
+      local errs = ""
+      for k, v in pairs(t) do
+        local _continue_0 = false
+        repeat
+          if not (AST.is_syntax_tree(v)) then
+            _continue_0 = true
+            break
+          end
+          local err = find_errors(v)
+          if #err > 0 then
+            if #errs > 0 then
+              errs = errs .. "\n\n"
+            end
+            errs = errs .. err
+          end
+          _continue_0 = true
+        until true
+        if not _continue_0 then
+          break
+        end
+      end
+      return errs
+    end
+    local errs = find_errors(tree)
+    if #errs > 0 then
+      error(errs, 0)
+    end
+    return tree
   end
   NomsuCompiler.can_optimize = function()
     return false
@@ -699,6 +819,10 @@ do
       return LuaCode.Value(tree.source, (tree[1]):as_lua_id())
     elseif "FileChunks" == _exp_0 then
       return error("Cannot convert FileChunks to a single block of lua, since each chunk's " .. "compilation depends on the earlier chunks")
+    elseif "Comment" == _exp_0 then
+      return LuaCode(tree.source, "")
+    elseif "Error" == _exp_0 then
+      return error("Cannot compile errors")
     else
       return error("Unknown type: " .. tostring(tree.type))
     end
@@ -726,6 +850,10 @@ do
     local _exp_0 = tree.type
     if "FileChunks" == _exp_0 then
       return error("Cannot inline a FileChunks")
+    elseif "Comment" == _exp_0 then
+      return NomsuCode(tree.source, "")
+    elseif "Error" == _exp_0 then
+      return error("Cannot compile errors")
     elseif "Action" == _exp_0 then
       local nomsu = NomsuCode(tree.source)
       if tree.target then
@@ -950,15 +1078,8 @@ do
       end
       local space = MAX_LINE - pos
       local inline
-      local check
-      check = function(prefix, nomsu, tree)
-        if type(tree) == 'number' then
-          require('ldt').breakpoint()
-        end
-        return coroutine.yield(prefix, nomsu, tree)
-      end
       for prefix, nomsu, tree in coroutine.wrap(function()
-        inline = self:tree_to_inline_nomsu(t, false, check)
+        inline = self:tree_to_inline_nomsu(t, false, coroutine.yield)
       end) do
         local len = #tostring(nomsu)
         if prefix + len > MAX_LINE then
@@ -1197,7 +1318,7 @@ do
       end
       nomsu:append(": ", recurse(value, #tostring(nomsu)))
       return nomsu
-    elseif "IndexChain" == _exp_0 or "Number" == _exp_0 or "Var" == _exp_0 then
+    elseif "IndexChain" == _exp_0 or "Number" == _exp_0 or "Var" == _exp_0 or "Comment" == _exp_0 or "Error" == _exp_0 then
       return self:tree_to_inline_nomsu(tree)
     else
       return error("Unknown type: " .. tostring(tree.type))
diff --git a/nomsu_compiler.moon b/nomsu_compiler.moon
index f388c2d..4300327 100644
--- a/nomsu_compiler.moon
+++ b/nomsu_compiler.moon
@@ -24,6 +24,7 @@ unpack or= table.unpack
 {:NomsuCode, :LuaCode, :Source} = require "code_obj"
 AST = require "syntax_tree"
 Parser = require("parser")
+make_parser = require("parser2")
 -- Mapping from source string (e.g. "@core/metaprogramming.nom[1:100]") to a mapping
 -- from lua line number to nomsu line number
 export SOURCE_MAP
@@ -37,15 +38,74 @@ table.copy = (t)-> setmetatable({k,v for k,v in pairs(t)}, getmetatable(t))
 -- consider non-linear codegen, rather than doing thunks for things like comprehensions
 -- Re-implement nomsu-to-lua comment translation?
 
+Parsers = {}
+max_parser_version = 0
+for version=1,999
+    continue unless version == 4 -- TODO: remove
+    peg_file = io.open("nomsu.#{version}.peg")
+    if not peg_file and package.nomsupath
+        for path in package.nomsupath\gmatch("[^;]+")
+            peg_file = io.open(path.."/nomsu.#{version}.peg")
+            break if peg_file
+    break unless peg_file
+    max_parser_version = version
+    make_tree = (tree, userdata)->
+        cls = AST[tree.type]
+        tree.source = Source(userdata.filename, tree.start, tree.stop)
+        tree.start, tree.stop = nil, nil
+        tree.type = nil
+        tree.comments = [t for t in *tree when AST.is_syntax_tree(t, "Comment")]
+        if #tree.comments == 0 then tree.comments = nil
+        for i=#tree,1,-1
+            if AST.is_syntax_tree(tree[i], "Comment")
+                table.remove(tree, i)
+        tree = setmetatable(tree, cls)
+        cls.source_code_for_tree[tree] = userdata.source
+        if tree.__init then tree\__init!
+        return tree
+    Parsers[version] = make_parser(peg_file\read("*a"), make_tree)
+    peg_file\close!
+
 MAX_LINE = 80 -- For beautification purposes, try not to make lines much longer than this value
 NomsuCompiler = setmetatable {name:"Nomsu"},
     __index: (k)=> if _self = rawget(@, "self") then _self[k] else nil
     __tostring: => @name
+_anon_chunk = 0
 with NomsuCompiler
     .NOMSU_COMPILER_VERSION = 7
-    .NOMSU_SYNTAX_VERSION = Parser.version
+    .NOMSU_SYNTAX_VERSION = max_parser_version
     .nomsu = NomsuCompiler
-    .parse = (...)=> Parser.parse(...)
+    .parse = (nomsu_code, source=nil, version=nil)=>
+        source or= nomsu_code.source
+        nomsu_code = tostring(nomsu_code)
+        unless source
+            source = Source("anonymous chunk ##{_anon_chunk}", 1, #nomsu_code)
+            _anon_chunk += 1
+        version or= nomsu_code\match("^#![^\n]*nomsu[ ]+-V[ ]*([0-9.]+)")
+        syntax_version = version and tonumber(version\match("^[0-9]+")) or max_parser_version
+        parse = Parsers[syntax_version] or Parsers[max_parser_version]
+        tree = parse(nomsu_code, source.filename)
+        pretty_error = require("pretty_errors")
+        -- TODO: truncate
+        find_errors = (t)->
+            if t.type == "Error"
+                return pretty_error{
+                    error:t.error, hint:t.hint, source:t\get_source_code!
+                    start:t.source.start, stop:t.source.stop
+                }
+            errs = ""
+            for k,v in pairs(t)
+                continue unless AST.is_syntax_tree(v)
+                err = find_errors(v)
+                if #err > 0
+                    if #errs > 0 then errs ..="\n\n"
+                    errs ..= err
+            return errs
+
+        errs = find_errors(tree)
+        if #errs > 0
+            error(errs, 0)
+        return tree
     .can_optimize = -> false
 
     -- Discretionary/convenience stuff
@@ -457,6 +517,13 @@ with NomsuCompiler
             when "FileChunks"
                 error("Cannot convert FileChunks to a single block of lua, since each chunk's "..
                     "compilation depends on the earlier chunks")
+            
+            when "Comment"
+                -- TODO: implement?
+                return LuaCode(tree.source, "")
+            
+            when "Error"
+                error("Cannot compile errors")
 
             else
                 error("Unknown type: #{tree.type}")
@@ -467,6 +534,13 @@ with NomsuCompiler
         switch tree.type
             when "FileChunks"
                 error("Cannot inline a FileChunks")
+            
+            when "Comment"
+                -- TODO: implement?
+                return NomsuCode(tree.source, "")
+            
+            when "Error"
+                error("Cannot compile errors")
 
             when "Action"
                 nomsu = NomsuCode(tree.source)
@@ -601,10 +675,7 @@ with NomsuCompiler
             if type(pos) != 'number' then pos = #tostring(pos)\match("[ ]*([^\n]*)$")
             space = MAX_LINE - pos
             local inline
-            check = (prefix,nomsu,tree)->
-                if type(tree) == 'number' then require('ldt').breakpoint!
-                coroutine.yield(prefix,nomsu,tree)
-            for prefix, nomsu, tree in coroutine.wrap(-> inline = @tree_to_inline_nomsu(t, false, check))
+            for prefix, nomsu, tree in coroutine.wrap(-> inline = @tree_to_inline_nomsu(t, false, coroutine.yield))
                 len = #tostring(nomsu)
                 break if prefix+len > MAX_LINE
                 break if tree.type == "Block" and (#tree > 1 or len > 20)
@@ -779,7 +850,7 @@ with NomsuCompiler
                 nomsu\append ": ", recurse(value, #tostring(nomsu))
                 return nomsu
             
-            when "IndexChain", "Number", "Var"
+            when "IndexChain", "Number", "Var", "Comment", "Error"
                 return @tree_to_inline_nomsu tree
             
             else
diff --git a/parser.lua b/parser.lua
index 4662f5e..8a94314 100644
--- a/parser.lua
+++ b/parser.lua
@@ -47,7 +47,7 @@ do
     return string.char(tonumber(self))
   end)
   _with_0.escaped_char = _with_0.escaped_char + ((P("\\") * C(S("ntbavfr"))) / string_escapes)
-  _with_0.operator_char = S("'`~!@$^&*-+=|<>?/")
+  _with_0.operator_char = S("'`~!@$^&*+=|<>?/-")
   _with_0.utf8_char = (R("\194\223") * R("\128\191") + R("\224\239") * R("\128\191") * R("\128\191") + R("\240\244") * R("\128\191") * R("\128\191") * R("\128\191"))
   _with_0.ident_char = R("az", "AZ", "09") + P("_") + _with_0.utf8_char
   _with_0.userdata = Carg(1)
diff --git a/parser.moon b/parser.moon
index 0e68b4d..f2e5b17 100644
--- a/parser.moon
+++ b/parser.moon
@@ -21,7 +21,7 @@ NOMSU_DEFS = with {}
     .escaped_char = (P("\\")*S("xX")*C(hex*hex)) / => string.char(tonumber(@, 16))
     .escaped_char += (P("\\")*C(digit*(digit^-2))) / => string.char(tonumber @)
     .escaped_char += (P("\\")*C(S("ntbavfr"))) / string_escapes
-    .operator_char = S("'`~!@$^&*-+=|<>?/")
+    .operator_char = S("'`~!@$^&*+=|<>?/-")
     .utf8_char = (
         R("\194\223")*R("\128\191") +
         R("\224\239")*R("\128\191")*R("\128\191") +
diff --git a/parser2.moon b/parser2.moon
new file mode 100644
index 0000000..9a2e2ff
--- /dev/null
+++ b/parser2.moon
@@ -0,0 +1,64 @@
+-- This file contains the parser, which converts text into abstract syntax trees
+lpeg = require 'lpeg'
+re = require 're'
+lpeg.setmaxstack 20000
+{:P,:R,:S,:C,:Cmt,:Carg,:Cc} = lpeg
+{:repr} = require 'utils'
+
+DEFS = with {}
+    -- Newline supports either windows-style CR+LF or unix-style LF
+    .nl = P("\r")^-1 * P("\n")
+    .tab = P("\t")
+    .tonumber = tonumber
+    .tochar = string.char
+    .unpack = unpack or table.unpack
+    .nil = Cc(nil)
+    .userdata = Carg(1)
+    .utf8_char = (
+        R("\194\223")*R("\128\191") +
+        R("\224\239")*R("\128\191")*R("\128\191") +
+        R("\240\244")*R("\128\191")*R("\128\191")*R("\128\191"))
+    .Tree = (t, userdata)-> userdata.make_tree(t, userdata)
+
+setmetatable(DEFS, {__index:(key)=>
+    if i = key\match("^ascii_(%d+)$")
+        c = string.char(tonumber(i))
+        self[key] = c
+        return c
+    elseif i = key\match("^number_(%d+)$")
+        p = Cc(tonumber(i))
+        self[key] = p
+        return p
+})
+
+-- Just for cleanliness, I put the language spec in its own file using a slightly modified
+-- version of the lpeg.re syntax.
+peg_tidier = re.compile [[
+file <- %nl* {~ (def/comment) (%nl+ (def/comment))* %nl* ~}
+def <- anon_def / captured_def
+anon_def <-
+    ({ident} (" "*) ":" {[^%nl]* (%nl+ " "+ [^%nl]*)*}) 
+    -> "%1 <- %2"
+captured_def <-
+    ({ident} (" "*) "(" {ident} ")" (" "*) ":" {[^%nl]* (%nl+ " "+ [^%nl]*)*})
+    -> "%1 <- ({| {:start:{}:} %3 {:stop:{}:} {:type: (''->'%2') :} |} %%userdata) -> Tree"
+ident <- [a-zA-Z_][a-zA-Z0-9_]*
+comment <- "--" [^%nl]*
+]]
+
+make_parser = (peg, make_tree=nil)->
+    peg = assert(peg_tidier\match(peg))
+    peg = assert(re.compile(peg, DEFS))
+    return (input, filename='???')->
+        input = tostring(input)
+        tree_mt = {__index: {source:input, filename:filename}}
+        userdata = {
+            make_tree: make_tree or ((t)->setmetatable(t, tree_mt))
+            :filename, source:input
+        }
+        tree = peg\match(input, nil, userdata)
+        if not tree
+            error "File #{filename} failed to parse:\n#{input}"
+        return tree
+
+return make_parser
diff --git a/pretty_errors.lua b/pretty_errors.lua
new file mode 100644
index 0000000..f2a608e
--- /dev/null
+++ b/pretty_errors.lua
@@ -0,0 +1,60 @@
+require("containers")
+local string2 = require('string2')
+local box
+box = function(text)
+  local max_line = 0
+  for line in text:gmatch("[^\n]+") do
+    max_line = math.max(max_line, #(line:gsub("\027%[[0-9;]*m", "")))
+  end
+  local ret = ("\n" .. text):gsub("\n([^\n]*)", function(line)
+    local line_len = #(line:gsub("\027%[[0-9;]*m", ""))
+    return "\n" .. tostring(line) .. tostring((" "):rep(max_line - line_len)) .. " \027[0m"
+  end)
+  return ret:sub(2, -1), max_line
+end
+local format_error
+format_error = function(err)
+  local context = err.context or 2
+  local err_line, err_linenum, err_linepos = string2.line_at(err.source, err.start)
+  local err_size = math.min((err.stop - err.start), (#err_line - err_linepos) + 1)
+  local nl_indicator = (err_linepos > #err_line) and " " or ""
+  local fmt_str = " %" .. tostring(#tostring(err_linenum + context)) .. "d|"
+  local pointer
+  if err_size >= 2 then
+    pointer = (" "):rep(err_linepos + #fmt_str:format(0) - 1) .. "╚" .. tostring(("═"):rep(err_size - 2)) .. "╝"
+  else
+    pointer = (" "):rep(err_linepos + #fmt_str:format(0) - 1) .. "⬆"
+  end
+  local err_msg = "\027[33;41;1mParse error at " .. tostring(err.filename) .. ":" .. tostring(err_linenum) .. "\027[0m"
+  for i = err_linenum - context, err_linenum - 1 do
+    do
+      local line = string2.line(err.source, i)
+      if line then
+        err_msg = err_msg .. "\n\027[2m" .. tostring(fmt_str:format(i)) .. "\027[0m" .. tostring(line) .. "\027[0m"
+      end
+    end
+  end
+  if err_line then
+    local box_width = 60
+    local before = err_line:sub(1, err_linepos - 1)
+    local during = err_line:sub(err_linepos, err_linepos + err_size - 1)
+    local after = err_line:sub(err_linepos + err_size, -1)
+    err_line = "\027[0m" .. tostring(before) .. "\027[41;30m" .. tostring(during) .. tostring(nl_indicator) .. "\027[0m" .. tostring(after)
+    err_msg = err_msg .. "\n\027[2m" .. tostring(fmt_str:format(err_linenum)) .. tostring(err_line) .. "\027[0m\n" .. tostring(pointer)
+    local err_text = "\027[47;31;1m" .. tostring((" " .. err.error):wrap_to_1(box_width):gsub("\n", "\n\027[47;31;1m "))
+    if err.hint then
+      err_text = err_text .. "\n\027[47;30m" .. tostring((" Suggestion: " .. tostring(err.hint)):wrap_to_1(box_width):gsub("\n", "\n\027[47;30m "))
+    end
+    err_msg = err_msg .. ("\n\027[33;1m " .. box(err_text):gsub("\n", "\n "))
+  end
+  for i = err_linenum + 1, err_linenum + context do
+    do
+      local line = string2.line(err.source, i)
+      if line then
+        err_msg = err_msg .. "\n\027[2m" .. tostring(fmt_str:format(i)) .. "\027[0m" .. tostring(line) .. "\027[0m"
+      end
+    end
+  end
+  return err_msg
+end
+return format_error
diff --git a/pretty_errors.moon b/pretty_errors.moon
new file mode 100644
index 0000000..3adada5
--- /dev/null
+++ b/pretty_errors.moon
@@ -0,0 +1,46 @@
+-- This file has code for converting errors to user-friendly format, with colors,
+-- line numbers, code excerpts, and so on.
+require "containers"
+string2 = require 'string2'
+
+box = (text)->
+    max_line = 0
+    for line in text\gmatch("[^\n]+")
+        max_line = math.max(max_line, #(line\gsub("\027%[[0-9;]*m","")))
+    ret = ("\n"..text)\gsub "\n([^\n]*)", (line)->
+        line_len = #(line\gsub("\027%[[0-9;]*m",""))
+        return "\n#{line}#{(" ")\rep(max_line-line_len)} \027[0m"
+    return ret\sub(2,-1), max_line
+
+format_error = (err)->
+    context = err.context or 2
+    err_line, err_linenum, err_linepos = string2.line_at(err.source, err.start)
+    -- TODO: better handle multi-line errors
+    err_size = math.min((err.stop - err.start), (#err_line-err_linepos) + 1)
+    nl_indicator = (err_linepos > #err_line) and " " or ""
+    fmt_str = " %#{#tostring(err_linenum+context)}d|"
+    pointer = if err_size >= 2
+        (" ")\rep(err_linepos+#fmt_str\format(0)-1).."╚#{("═")\rep(err_size-2)}╝"
+    else
+        (" ")\rep(err_linepos+#fmt_str\format(0)-1).."⬆"
+    err_msg = "\027[33;41;1mParse error at #{err.filename}:#{err_linenum}\027[0m"
+    for i=err_linenum-context,err_linenum-1
+        if line = string2.line(err.source, i)
+            err_msg ..= "\n\027[2m#{fmt_str\format(i)}\027[0m#{line}\027[0m"
+    if err_line
+        box_width = 60
+        before = err_line\sub(1, err_linepos-1)
+        during = err_line\sub(err_linepos,err_linepos+err_size-1)
+        after = err_line\sub(err_linepos+err_size, -1)
+        err_line = "\027[0m#{before}\027[41;30m#{during}#{nl_indicator}\027[0m#{after}"
+        err_msg ..= "\n\027[2m#{fmt_str\format(err_linenum)}#{err_line}\027[0m\n#{pointer}"
+        err_text = "\027[47;31;1m#{(" "..err.error)\wrap_to_1(box_width)\gsub("\n", "\n\027[47;31;1m ")}"
+        if err.hint
+            err_text ..= "\n\027[47;30m#{(" Suggestion: #{err.hint}")\wrap_to_1(box_width)\gsub("\n", "\n\027[47;30m ")}"
+        err_msg ..= "\n\027[33;1m "..box(err_text)\gsub("\n", "\n ")
+    for i=err_linenum+1,err_linenum+context
+        if line = string2.line(err.source, i)
+            err_msg ..= "\n\027[2m#{fmt_str\format(i)}\027[0m#{line}\027[0m"
+    return err_msg
+
+return format_error
diff --git a/string2.lua b/string2.lua
new file mode 100644
index 0000000..387fd65
--- /dev/null
+++ b/string2.lua
@@ -0,0 +1,134 @@
+local reverse, upper, lower, find, byte, match, gmatch, gsub, sub, format, rep, char
+do
+  local _obj_0 = string
+  reverse, upper, lower, find, byte, match, gmatch, gsub, sub, format, rep, char = _obj_0.reverse, _obj_0.upper, _obj_0.lower, _obj_0.find, _obj_0.byte, _obj_0.match, _obj_0.gmatch, _obj_0.gsub, _obj_0.sub, _obj_0.format, _obj_0.rep, _obj_0.char
+end
+local isplit
+isplit = function(self, sep)
+  if sep == nil then
+    sep = '%s+'
+  end
+  local step
+  step = function(self, i)
+    local start = self.pos
+    if not (start) then
+      return 
+    end
+    i = i + 1
+    local nl = find(self.str, self.sep, start)
+    self.pos = nl and (nl + 1) or nil
+    local line = sub(self.str, start, nl and (nl - 1) or #self.str)
+    return i, line, start, (nl and (nl - 1) or #self.str)
+  end
+  return step, {
+    str = self,
+    pos = 1,
+    sep = sep
+  }, 0
+end
+local string2 = {
+  isplit = isplit,
+  uppercase = upper,
+  lowercase = lower,
+  reversed = reverse,
+  capitalized = function(self)
+    return gsub(self, '%l', upper, 1)
+  end,
+  byte = byte,
+  bytes = function(self, i, j)
+    return {
+      byte(self, i or 1, j or -1)
+    }
+  end,
+  split = function(self, sep)
+    local _accum_0 = { }
+    local _len_0 = 1
+    for i, chunk in isplit(self, sep) do
+      _accum_0[_len_0] = chunk
+      _len_0 = _len_0 + 1
+    end
+    return _accum_0
+  end,
+  lines = function(self)
+    local _accum_0 = { }
+    local _len_0 = 1
+    for i, line in isplit(self, '\n') do
+      _accum_0[_len_0] = line
+      _len_0 = _len_0 + 1
+    end
+    return _accum_0
+  end,
+  line = function(self, line_num)
+    for i, line, start in isplit(self, '\n') do
+      if i == line_num then
+        return line
+      end
+    end
+  end,
+  line_at = function(self, pos)
+    assert(type(pos) == 'number', "Invalid string position")
+    if pos < 1 or pos > #self then
+      return 
+    end
+    for i, line, start, stop in isplit(self, '\n') do
+      if stop >= pos then
+        return line, i, (pos - start + 1)
+      end
+    end
+  end,
+  wrap = function(self, maxlen, buffer)
+    if maxlen == nil then
+      maxlen = 80
+    end
+    if buffer == nil then
+      buffer = 8
+    end
+    local lines = { }
+    local _list_0 = self:lines()
+    for _index_0 = 1, #_list_0 do
+      local line = _list_0[_index_0]
+      while #line > maxlen do
+        local chunk = line:sub(1, maxlen)
+        local split = chunk:find(' ', maxlen - buffer, true) or maxlen
+        chunk = line:sub(1, split)
+        line = line:sub(split + 1, -1)
+        lines[#lines + 1] = chunk
+      end
+      lines[#lines + 1] = line
+    end
+    return table.concat(lines, "\n")
+  end,
+  as_lua_id = function(str)
+    local orig = str
+    str = gsub(str, "^ *$", "%1 ")
+    str = gsub(str, "x([0-9A-F][0-9A-F])", "x78%1")
+    str = gsub(str, "%W", function(c)
+      if c == ' ' then
+        return '_'
+      else
+        return format("x%02X", byte(c))
+      end
+    end)
+    str = gsub(str, "^_*%d", "_%1")
+    if str.from_lua_id then
+      local re_orig = str:from_lua_id()
+      if re_orig ~= orig then
+        require('ldt').breakpoint()
+      end
+    end
+    return str
+  end,
+  from_lua_id = function(str)
+    str = gsub(str, "^_(_*%d.*)", "%1")
+    str = gsub(str, "_", " ")
+    str = gsub(str, "x([0-9A-F][0-9A-F])", function(hex)
+      return char(tonumber(hex, 16))
+    end)
+    str = gsub(str, "^ ([ ]*)$", "%1")
+    return str
+  end
+}
+for k, v in pairs(string) do
+  string2[k] = string2[k] or v
+end
+return string2
diff --git a/string2.moon b/string2.moon
new file mode 100644
index 0000000..735a2cb
--- /dev/null
+++ b/string2.moon
@@ -0,0 +1,79 @@
+-- Expand the capabilities of the built-in strings
+{:reverse, :upper, :lower, :find, :byte, :match, :gmatch, :gsub, :sub, :format, :rep, :char} = string
+
+isplit = (sep='%s+')=>
+    step = (i)=>
+        start = @pos
+        return unless start
+        i += 1
+        nl = find(@str, @sep, start)
+        @pos = nl and (nl+1) or nil
+        line = sub(@str, start, nl and (nl-1) or #@str)
+        return i, line, start, (nl and (nl-1) or #@str)
+    return step, {str:@, pos:1, :sep}, 0
+
+string2 = {
+    :isplit, uppercase:upper, lowercase:lower, reversed:reverse
+    capitalized: => gsub(@, '%l', upper, 1)
+    byte: byte, bytes: (i, j)=> {byte(@, i or 1, j or -1)}
+    split: (sep)=> [chunk for i,chunk in isplit(@, sep)]
+    lines: => [line for i,line in isplit(@, '\n')]
+    line: (line_num)=>
+        for i, line, start in isplit(@, '\n')
+            return line if i == line_num
+
+    line_at: (pos)=>
+        assert(type(pos) == 'number', "Invalid string position")
+        return if pos < 1 or pos > #@
+        for i, line, start, stop in isplit(@, '\n')
+            if stop >= pos
+                return line, i, (pos-start+1)
+
+    wrap: (maxlen=80, buffer=8)=>
+        lines = {}
+        for line in *@lines!
+            while #line > maxlen
+                chunk = line\sub(1, maxlen)
+                split = chunk\find(' ', maxlen-buffer, true) or maxlen
+                chunk = line\sub(1, split)
+                line = line\sub(split+1, -1)
+                lines[#lines+1] = chunk
+            lines[#lines+1] = line
+        return table.concat(lines, "\n")
+
+    -- Convert an arbitrary text into a valid Lua identifier. This function is injective,
+    -- but not idempotent. In logic terms: (x != y) => (as_lua_id(x) != as_lua_id(y)),
+    -- but not (as_lua_id(a) == b) => (as_lua_id(b) == b).
+    as_lua_id: (str)->
+        orig = str
+        -- Empty strings are not valid lua identifiers, so treat them like " ",
+        -- and treat " " as "  ", etc. to preserve injectivity.
+        str = gsub str, "^ *$", "%1 "
+        -- Escape 'x' (\x78) when it precedes something that looks like an uppercase hex sequence.
+        -- This way, all Lua IDs can be unambiguously reverse-engineered, but normal usage
+        -- of 'x' won't produce ugly Lua IDs.
+        -- i.e. "x" -> "x", "oxen" -> "oxen", but "Hex2Dec" -> "Hex782Dec" and "He-ec" -> "Hex2Dec"
+        str = gsub str, "x([0-9A-F][0-9A-F])", "x78%1"
+        -- Map spaces to underscores, and everything else non-alphanumeric to hex escape sequences
+        str = gsub str, "%W", (c)->
+            if c == ' ' then '_'
+            else format("x%02X", byte(c))
+        -- Lua IDs can't start with numbers, so map "1" -> "_1", "_1" -> "__1", etc.
+        str = gsub str, "^_*%d", "_%1"
+        if str.from_lua_id
+            re_orig = str\from_lua_id!
+            require('ldt').breakpoint! if re_orig != orig
+        return str
+
+    -- from_lua_id(as_lua_id(str)) == str, but behavior is unspecified for inputs that
+    -- did not come from as_lua_id()
+    from_lua_id: (str)->
+        str = gsub(str, "^_(_*%d.*)", "%1")
+        str = gsub(str, "_", " ")
+        str = gsub(str, "x([0-9A-F][0-9A-F])", (hex)-> char(tonumber(hex, 16)))
+        str = gsub(str, "^ ([ ]*)$", "%1")
+        return str
+}
+for k,v in pairs(string) do string2[k] or= v
+
+return string2
diff --git a/syntax_tree.lua b/syntax_tree.lua
index 8fa15b7..b4cf45e 100644
--- a/syntax_tree.lua
+++ b/syntax_tree.lua
@@ -26,7 +26,9 @@ local types = {
   "DictEntry",
   "IndexChain",
   "Action",
-  "FileChunks"
+  "FileChunks",
+  "Error",
+  "Comment"
 }
 for _index_0 = 1, #types do
   local name = types[_index_0]
@@ -49,6 +51,10 @@ for _index_0 = 1, #types do
         return Source:is_instance(x) and tostring(x) or nil
       end)))
     end
+    cls.source_code_for_tree = { }
+    cls.get_source_code = function(self)
+      return self.source_code_for_tree[self]
+    end
     cls.map = function(self, fn)
       local replacement = fn(self)
       if replacement == false then
diff --git a/syntax_tree.moon b/syntax_tree.moon
index 96230a1..2f46d9e 100644
--- a/syntax_tree.moon
+++ b/syntax_tree.moon
@@ -10,7 +10,7 @@ AST.is_syntax_tree = (n, t=nil)->
     type(n) == 'table' and getmetatable(n) and AST[n.type] == getmetatable(n) and (t == nil or n.type == t)
 
 types = {"Number", "Var", "Block", "EscapedNomsu", "Text", "List", "Dict", "DictEntry",
-    "IndexChain", "Action", "FileChunks"}
+    "IndexChain", "Action", "FileChunks", "Error", "Comment"}
 for name in *types
     cls = {}
     with cls
@@ -21,6 +21,8 @@ for name in *types
         .is_instance = (x)=> getmetatable(x) == @
         .__tostring = => "#{@type}#{repr @, ((x)-> Source\is_instance(x) and tostring(x) or nil)}"
         .__repr = => "#{@type}#{repr @, ((x)-> Source\is_instance(x) and tostring(x) or nil)}"
+        .source_code_for_tree = {}
+        .get_source_code = => @source_code_for_tree[@]
         .map = (fn)=>
             replacement = fn(@)
             if replacement == false then return nil