diff --git a/bootstrap.lua b/bootstrap.lua
index 27a1953..97a565d 100644
--- a/bootstrap.lua
+++ b/bootstrap.lua
@@ -14,7 +14,7 @@ local fail_at
 fail_at = require('nomsu_compiler').fail_at
 local MAX_LINE = 80
 local compile_actions = {
-  [""] = function(self, fn, ...)
+  [""] = function(self, _t, fn, ...)
     local lua = LuaCode()
     local fn_lua = self:compile(fn)
     lua:add(fn_lua)
@@ -31,7 +31,7 @@ local compile_actions = {
     lua:add(")")
     return lua
   end,
-  ["Lua"] = function(self, code)
+  ["Lua"] = function(self, _t, code)
     if not code then
       return LuaCode("LuaCode()")
     end
@@ -62,7 +62,7 @@ local compile_actions = {
     end
     return operate_on_text(code)
   end,
-  ["lua >"] = function(self, code)
+  ["lua >"] = function(self, _t, code)
     if code.type ~= "Text" then
       return code
     end
@@ -83,7 +83,7 @@ local compile_actions = {
     end
     return operate_on_text(code)
   end,
-  ["= lua"] = function(self, code)
+  ["= lua"] = function(self, _t, code)
     return self:compile(SyntaxTree({
       type = "Action",
       "lua",
@@ -91,19 +91,19 @@ local compile_actions = {
       code
     }))
   end,
-  ["1 as lua"] = function(self, code)
+  ["1 as lua"] = function(self, _t, code)
     return LuaCode("_ENV:compile(", self:compile(code), ")")
   end,
-  ["use"] = function(self, path)
+  ["use"] = function(self, _t, path)
     return LuaCode("_ENV:use(" .. tostring(self:compile(path)) .. ")")
   end,
-  ["export"] = function(self, path)
+  ["export"] = function(self, _t, path)
     return LuaCode("_ENV:export(" .. tostring(self:compile(path)) .. ")")
   end,
-  ["run"] = function(self, path)
+  ["run"] = function(self, _t, path)
     return LuaCode("_ENV:run(" .. tostring(self:compile(path)) .. ")")
   end,
-  ["test"] = function(self, body)
+  ["test"] = function(self, _t, body)
     if not (body.type == 'Block') then
       fail_at(body, "Compile error: This should be a Block")
     end
@@ -121,22 +121,22 @@ local compile_actions = {
     }))
     return LuaCode("TESTS[" .. tostring(tostring(body.source):as_lua()) .. "] = ", test_text)
   end,
-  ["is jit"] = function(self, code)
+  ["is jit"] = function(self, _t, code)
     return LuaCode("jit")
   end,
-  ["Lua version"] = function(self, code)
+  ["Lua version"] = function(self, _t, code)
     return LuaCode("_VERSION")
   end,
-  ["nomsu environment"] = function(self)
+  ["nomsu environment"] = function(self, _t)
     return LuaCode("_ENV")
   end,
-  ["nomsu environment name"] = function(self)
+  ["nomsu environment name"] = function(self, _t)
     return LuaCode('"_ENV"')
   end,
-  ["this file was run directly"] = function(self)
+  ["this file was run directly"] = function(self, _t)
     return LuaCode('WAS_RUN_DIRECTLY')
   end,
-  ["the command line arguments"] = function(self)
+  ["the command line arguments"] = function(self, _t)
     return LuaCode('COMMAND_LINE_ARGS')
   end
 }
diff --git a/bootstrap.moon b/bootstrap.moon
index aca2dd7..d30e56b 100644
--- a/bootstrap.moon
+++ b/bootstrap.moon
@@ -8,7 +8,7 @@ Files = require "files"
 
 MAX_LINE = 80 -- For beautification purposes, try not to make lines much longer than this value
 compile_actions = {
-    [""]: (fn, ...)=>
+    [""]: (_t, fn, ...)=>
         lua = LuaCode!
         fn_lua = @compile(fn)
         lua\add fn_lua
@@ -21,7 +21,7 @@ compile_actions = {
         lua\add ")"
         return lua
 
-    ["Lua"]: (code)=>
+    ["Lua"]: (_t, code)=>
         if not code
             return LuaCode("LuaCode()")
         if code.type != "Text"
@@ -58,7 +58,7 @@ compile_actions = {
 
         return operate_on_text code
 
-    ["lua >"]: (code)=>
+    ["lua >"]: (_t, code)=>
         if code.type != "Text"
             return code
         operate_on_text = (text)->
@@ -73,22 +73,22 @@ compile_actions = {
             return lua
         return operate_on_text code
 
-    ["= lua"]: (code)=>
+    ["= lua"]: (_t, code)=>
         @compile(SyntaxTree{type:"Action", "lua", ">", code})
 
-    ["1 as lua"]: (code)=>
+    ["1 as lua"]: (_t, code)=>
         LuaCode("_ENV:compile(", @compile(code), ")")
 
-    ["use"]: (path)=>
+    ["use"]: (_t, path)=>
         LuaCode("_ENV:use(#{@compile(path)})")
 
-    ["export"]: (path)=>
+    ["export"]: (_t, path)=>
         LuaCode("_ENV:export(#{@compile(path)})")
 
-    ["run"]: (path)=>
+    ["run"]: (_t, path)=>
         LuaCode("_ENV:run(#{@compile(path)})")
 
-    ["test"]: (body)=>
+    ["test"]: (_t, body)=>
         unless body.type == 'Block'
             fail_at(body, "Compile error: This should be a Block")
         test_nomsu = body\get_source_code!\match(":[ ]*(.*)")
@@ -97,12 +97,12 @@ compile_actions = {
         test_text = @compile(SyntaxTree{type:"Text", source:body.source, test_nomsu})
         return LuaCode "TESTS[#{tostring(body.source)\as_lua!}] = ", test_text
 
-    ["is jit"]: (code)=> LuaCode("jit")
-    ["Lua version"]: (code)=> LuaCode("_VERSION")
-    ["nomsu environment"]: ()=> LuaCode("_ENV")
-    ["nomsu environment name"]: ()=> LuaCode('"_ENV"')
-    ["this file was run directly"]: => LuaCode('WAS_RUN_DIRECTLY')
-    ["the command line arguments"]: => LuaCode('COMMAND_LINE_ARGS')
+    ["is jit"]: (_t, code)=> LuaCode("jit")
+    ["Lua version"]: (_t, code)=> LuaCode("_VERSION")
+    ["nomsu environment"]: (_t)=> LuaCode("_ENV")
+    ["nomsu environment name"]: (_t)=> LuaCode('"_ENV"')
+    ["this file was run directly"]: (_t)=> LuaCode('WAS_RUN_DIRECTLY')
+    ["the command line arguments"]: (_t)=> LuaCode('COMMAND_LINE_ARGS')
 }
 
 return compile_actions
diff --git a/lib/compatibility/4.10.12.7.nom b/lib/compatibility/4.10.12.7.nom
index eeff2f2..be53cb6 100644
--- a/lib/compatibility/4.10.12.7.nom
+++ b/lib/compatibility/4.10.12.7.nom
@@ -63,10 +63,8 @@ upgrade $tree to "4.10.12.7" as:
             $i += 1
         return
         --- (insert chunk) ---
-        [$chunk1, $chunk2] = [
-            SyntaxTree {.type = "Block", .source = $first_chunk.source}
-            SyntaxTree {.type = "Block", .source = $first_chunk.source}
-        ]
+        [$chunk1, $chunk2] =
+            ["Block" tree from $first_chunk.source, "Block" tree from $first_chunk.source]
         
         for $j in 1 to ($i - 1):
             $chunk1.$j = $first_chunk.$j
@@ -74,8 +72,7 @@ upgrade $tree to "4.10.12.7" as:
         for $j in $i to (size of $first_chunk):
             $chunk2.($j - $i + 1) = $first_chunk.$j
         
-        $new_tree =
-            SyntaxTree {.source = $tree.source, .type = "FileChunks"} $chunk1 $chunk2
+        $new_tree = ("FileChunks" tree from $tree.source with $chunk1 $chunk2)
         
         for $i in 2 to (size of $tree):
             $new_tree.($i + 1) = $tree.$i
diff --git a/lib/compatibility/4.11.nom b/lib/compatibility/4.11.nom
index 053e1c8..e30734d 100644
--- a/lib/compatibility/4.11.nom
+++ b/lib/compatibility/4.11.nom
@@ -25,7 +25,7 @@ upgrade action "set" to "4.11" via
         for $entry in $tree.2 at $i:
             $lhs.$i = $entry.1
             $rhs.$i = $entry.2
-        return (SyntaxTree {.type = "Action", .source = $tree.source} $lhs "=" $rhs)
+        return ("Action" tree from $tree.source with $lhs "=" $rhs)
 
 upgrade action "1 with 2 ~>" to "4.11" via
     for $tree:
diff --git a/lib/compatibility/6.14.nom b/lib/compatibility/6.14.nom
index 0e742d0..b11474b 100644
--- a/lib/compatibility/6.14.nom
+++ b/lib/compatibility/6.14.nom
@@ -28,11 +28,11 @@ upgrade action (assume $assumption or barf $err) to "6.14" as
 
 upgrade action (barf $msg) to "6.14" as (fail $msg)
 upgrade action (\(1's meaning)).stub to "6.14" via
-    $tree -> (SyntaxTree {.source = $tree.source, .type = "Var", $tree.1})
+    $tree -> ("Var" tree from $tree.source with $tree.1)
 upgrade action (log base $b of $n) to "6.14" as (log $n base $b)
 upgrade action "use" to "6.14" via
     for $tree:
         $path = $tree.2.1
         $path = ($path, with "%.nom$" -> "")
         $path = ($path, with "^lib/" -> "")
-        return \(use (SyntaxTree {.source = $tree.2.source, .type = "Text"} $path))
+        return \(use ("Text" tree from $tree.2.source with $path))
diff --git a/lib/compatibility/compatibility.nom b/lib/compatibility/compatibility.nom
index 419f589..45ea1d6 100644
--- a/lib/compatibility/compatibility.nom
+++ b/lib/compatibility/compatibility.nom
@@ -43,7 +43,7 @@ external:
                     ($t is syntax tree):
                         $args = []
                         for $k = $v in $t:
-                            if ((type of $k) == "number"):
+                            if ((type of $k) == "a number"):
                                 $args, add (make tree $v)
                             ..else:
                                 $args, add "\($k)=\(make tree $v)"
diff --git a/lib/consolecolor/init.nom b/lib/consolecolor/init.nom
index 19dc5ea..27823b8 100644
--- a/lib/consolecolor/init.nom
+++ b/lib/consolecolor/init.nom
@@ -18,9 +18,8 @@ $colors = {
 
 for $name = $colornum in $colors:
     $colornum = "\$colornum"
-    $(COMPILE RULES).$name =
-        for ($compile $text):
-            if $text:
-                return (Lua "('\\027[\($colornum)m'..\($text as lua expr)..'\\027[0m')")
-            ..else:
-                return (Lua "'\\027[\($colornum)m'")
+    \($name \$text) compiles to:
+        if $text:
+            return (Lua "('\\027[\($colornum)m'..\($text as lua expr)..'\\027[0m')")
+        ..else:
+            return (Lua "'\\027[\($colornum)m'")
diff --git a/lib/core/errors.nom b/lib/core/errors.nom
index 0b67400..8027228 100644
--- a/lib/core/errors.nom
+++ b/lib/core/errors.nom
@@ -8,14 +8,15 @@ use "core/control_flow"
 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-(fail $msg) compiles to
-    LuaCode
-        "at_1_fail(\(quote $msg.source), 'Failure: '..\($msg as lua expr))"
-        ..if $msg else "error('Failure', 0)"
+(fail $msg) compiles to ("
+    at_1_fail(\(quote (this tree).source), 'Failure: \(
+        "'..\($msg as lua expr)" if $msg else "A failure was triggered here'"
+    ))
+")
 
 (assume $condition) compiles to ("
     if not \($condition as lua expr) then
-        at_1_fail(\(quote "\($condition.source)"), "Assumption failed: This is not true.")
+        at_1_fail(\(quote "\($condition.source)"), "Assumption failed: This was not true.")
     end
 ")
 
@@ -24,7 +25,7 @@ use "core/control_flow"
         local _a, _b = \($a as lua expr), \($b as lua expr)
         if _a ~= _b then
             at_1_fail(\(quote "\($a.source)"),
-                "Assumption failed: This value is "..tostring(_a)..", but it was supposed to be "..tostring(_b)..".")
+                "Assumption failed: This value was "..tostring(_a).." when it was supposed to be "..tostring(_b)..".")
         end
     end
 ")
@@ -34,7 +35,7 @@ use "core/control_flow"
         local _a, _b = \($a as lua expr), \($b as lua expr)
         if _a == _b then
             at_1_fail(\(quote "\($a.source)"),
-                "Assumption failed: This value is "..tostring(_a)..", but it wasn't supposed to be.")
+                "Assumption failed: This value was "..tostring(_a).." when it wasn't supposed to be.")
         end
     end
 ")
diff --git a/lib/core/metaprogramming.nom b/lib/core/metaprogramming.nom
index 76ccf4a..bfcc0bf 100644
--- a/lib/core/metaprogramming.nom
+++ b/lib/core/metaprogramming.nom
@@ -16,13 +16,16 @@ lua> ("
             end
         end
     end
-    COMPILE_RULES["define mangler"] = function(\(nomsu environment))
+    COMPILE_RULES["define mangler"] = function(\(nomsu environment), _tree)
         return LuaCode("local mangle = mangler()")
     end
+    COMPILE_RULES["this tree"] = function(\(nomsu environment), _tree)
+        return LuaCode("_tree")
+    end
 ")
 
 lua> ("
-    COMPILE_RULES["1 ->"] = function(\(nomsu environment), \$args, \$body)
+    COMPILE_RULES["1 ->"] = function(\(nomsu environment), _tree, \$args, \$body)
         if \$args and not \$body then \$args, \$body = {}, \$args end
         local body_lua = SyntaxTree:is_instance(\$body) and \(nomsu environment):compile(\$body) or \$body
         if SyntaxTree:is_instance(\$body) and \$body.type ~= "Block" then body_lua:prepend("return ") end
@@ -41,7 +44,7 @@ lua> ("
             elseif not arg_lua:is_lua_id() then
                 at_1_fail(SyntaxTree:is_instance(arg) and arg or nil,
                     "Compile error: This does not compile to a Lua identifier, so it "..
-                    "can't be used as a function argument."..
+                    "can't be used as a function argument. "..
                     "Hint: This should probably be a Nomsu variable instead (like $x).")
             end
             lua:add(i > 1 and ", " or "", arg_lua)
@@ -84,13 +87,29 @@ test:
         fail "compile to is leaking variables"
 
 lua> ("
-    COMPILE_RULES["1 compiles to"] = function(\(nomsu environment), \$action, \$body)
-        local \$args = List{"\(nomsu environment)", unpack(\$action:get_args())}
+    COMPILE_RULES["1 compiles to"] = function(\(nomsu environment), \(this tree), \$action, \$body)
+        local \$args = List{"\(nomsu environment)", "\(this tree)"}
         if \$body.type == "Text" then
             \$body = SyntaxTree{source=\$body.source, type="Action", "Lua", \$body}
         end
-        return LuaCode("COMPILE_RULES[", \$action:get_stub():as_lua(),
-            "] = ", \(\($args -> $body) as lua))
+        if not (\$action.type == "Action" or (\$action.type == "EscapedNomsu" and \$action[1]\
+    ...type == "Action")) then
+            at_1_fail(\$action.source, "Compile error: "..
+                "This is neither an action nor an escaped action. "..
+                "Hint: This should probably be an action like:\\n"
+                .."(foo $x) compiles to \\"(\\\\($x as lua) + 1)\\"")
+        end
+        if \$action.type == "EscapedNomsu" then
+            for _,a in ipairs(\$action[1]) do
+                if a.type == "EscapedNomsu" then \$args:add(a[1]) end
+            end
+            return LuaCode("COMPILE_RULES[", \($action as lua), ":get_stub()] = ",
+                \(\($args -> $body) as lua))
+        else
+            for _,a in ipairs(\$action:get_args()) do \$args:add(a) end
+            return LuaCode("COMPILE_RULES[", \$action:get_stub():as_lua(),
+                "] = ", \(\($args -> $body) as lua))
+        end
     end
 ")
 
@@ -102,19 +121,19 @@ lua> ("
             at_1_fail(\$actions, "Compile error: This should be a list of actions.")
         end
         local lua = \(\($actions.1 compiles to $body) as lua)
-        local \$args = List{"\(nomsu environment)", unpack(\$actions[1]:get_args())}
-        local \$compiled_args = List{"\(nomsu environment)"};
-        for i=2,#\$args do \$compiled_args[i] = \(nomsu environment):compile(\$args[i]) end
+        local \$args = List{"\(nomsu environment)", "\(this tree)", unpack(\$actions[1]:get_args())}
+        local \$compiled_args = List{"\(nomsu environment)", "\(this tree)"};
+        for i=3,#\$args do \$compiled_args[i] = \(nomsu environment):compile(\$args[i]) end
         for i=2,#\$actions do
             local alias = \$actions[i]
-            local \$alias_args = List{"\(nomsu environment)", unpack(alias:get_args())}
+            local \$alias_args = List{"\(nomsu environment)", "\(this tree)", unpack(alias:get_args())}
             lua:add("\\nCOMPILE_RULES[", alias:get_stub():as_lua(), "] = ")
             if \$alias_args == \$args then
                 lua:add("COMPILE_RULES[", \$actions[1]:get_stub():as_lua(), "]")
             else
                 lua:add("function(")
-                local \$compiled_alias_args = List{"\(nomsu environment)"};
-                for i=2,#\$alias_args do \$compiled_alias_args[i] = \(nomsu environment):compile(\$alias_args[i]) end
+                local \$compiled_alias_args = List{"\(nomsu environment)", "\(this tree)"};
+                for i=3,#\$alias_args do \$compiled_alias_args[i] = \(nomsu environment):compile(\$alias_args[i]) end
                 lua:concat_add(\$compiled_alias_args, ", ")
                 lua:add(") return COMPILE_RULES[", \$actions[1]:get_stub():as_lua(), "](")
                 lua:concat_add(\$compiled_args, ", ")
@@ -152,7 +171,7 @@ test:
             lua:add(\$action:get_stub():as_lua_id())
             lua:add_free_vars({\$action:get_stub():as_lua_id()})
         else
-            at_1_fail(\$action, "Compile error: Expected an action or method call here")
+            at_1_fail(\$action, "Compile error: This is not an action or method call.")
         end
         lua:add(" = ", \(\($action -> $body) as lua), ";")
         return lua
@@ -415,6 +434,7 @@ external:
         lua> ("
             local lua_type = \(lua type of $)
             if lua_type == 'string' then return 'Text'
+            elseif lua_type == 'nil' then return 'nil'
             elseif lua_type == 'table' or lua_type == 'userdata' then
                 local mt = getmetatable(\$)
                 if mt and mt.__type then return mt.__type end
@@ -427,6 +447,17 @@ external:
 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+test:
+    assume ("Action" tree with "foo" ("Var" tree with "x")) == \(foo \$x)
+
+external:
+    ($type tree with (*extra arguments*)) means
+        SyntaxTree (=lua "{type=\$type, ...}")
+    ($type tree from $source) means
+        SyntaxTree (=lua "{type=\$type, source=\$source}")
+    ($type tree from $source with (*extra arguments*)) means
+        SyntaxTree (=lua "{type=\$type, source=\$source, ...}")
+
 test:
     (foo) means:
         return 100 200 300
diff --git a/lib/core/things.nom b/lib/core/things.nom
index 104c8d0..5f74b1a 100644
--- a/lib/core/things.nom
+++ b/lib/core/things.nom
@@ -101,8 +101,8 @@ external:
                 $class_body with vars {
                     : for $v in $vars:
                         add ($v as lua expr, text) =
-                            SyntaxTree {.type = "IndexChain"} (SyntaxTree {.type = "Var"} "self")
-                                SyntaxTree {.type = "Index"} (SyntaxTree {.type = "Text"} $v.1)
+                            "IndexChain" tree with ("Var" tree with "self")
+                                "Index" tree with ("Text" tree with $v.1)
                 }
         $lua =
             Lua ("
diff --git a/lib/shell/init.nom b/lib/shell/init.nom
index d58894e..13dde56 100644
--- a/lib/shell/init.nom
+++ b/lib/shell/init.nom
@@ -1,12 +1,26 @@
 #
     This file defines some actions for running shell commands.
-    
+
 external:
-    (=sh $cmd) means:
-        lua> ("
-            local result = io.popen(\$cmd)
-            local contents = result:read("*a")
-            result:close()
-            return contents
-        ")
-    $(sh> $) = $os.execute
+    (at $callsite =sh $cmd) means:
+        $f = ($io.popen $cmd)
+        $contents = ($f, read "*a")
+        [$ok, $return_type, $return] = ($f, close)
+        unless $ok:
+            if ($return_type == "exit"):
+                at $callsite fail "Command failure: Command `\$cmd` failed with exit code \$return"
+            ..else:
+                at $callsite fail "Command failure: Command `\$cmd` was terminated by signal \$return"
+        return $contents
+
+    (at $callsite sh> $cmd) means:
+        [$ok, $return_type, $return] = ($os.execute $cmd)
+        unless $ok:
+            if ($return_type == "exit"):
+                at $callsite fail "Command failure: Command `\$cmd` failed with exit code \$return"
+            ..else:
+                at $callsite fail "Command failure: Command `\$cmd` was terminated by signal \$return"
+
+    # Attach callsite information for better error reporting
+    (=sh $cmd) compiles to (\(at ("Text" tree with "\($cmd.source)") =sh $cmd) as lua)
+    (sh> $cmd) compiles to (\(at ("Text" tree with "\($cmd.source)") sh> $cmd) as lua)
diff --git a/lib/tools/repl.nom b/lib/tools/repl.nom
index 63d9e30..ea0cc8a 100755
--- a/lib/tools/repl.nom
+++ b/lib/tools/repl.nom
@@ -68,7 +68,7 @@ command line program with $args:
                 $ret = (run $lua)
             ..if it fails with $err: say $err
             ..if it succeeds:
-                if (type of $ret) is:
+                if (lua type of $ret) is:
                     "nil":
                         do nothing
                     
diff --git a/nomsu_compiler.lua b/nomsu_compiler.lua
index c2502d8..542afe5 100644
--- a/nomsu_compiler.lua
+++ b/nomsu_compiler.lua
@@ -93,7 +93,7 @@ compile = function(self, tree)
         end
         args = _accum_0
       end
-      local ret = compile_action(self, unpack(args))
+      local ret = compile_action(self, tree, unpack(args))
       if ret == nil then
         local info = debug.getinfo(compile_action, "S")
         local filename = Source:from_string(info.source).filename
diff --git a/nomsu_compiler.moon b/nomsu_compiler.moon
index 0bb020c..e17d5e2 100644
--- a/nomsu_compiler.moon
+++ b/nomsu_compiler.moon
@@ -65,7 +65,7 @@ compile = (tree)=>
                 args = [arg for arg in *tree when type(arg) != "string"]
                 -- Force Lua to avoid tail call optimization for debugging purposes
                 -- TODO: use tail call?
-                ret = compile_action(@, unpack(args))
+                ret = compile_action(@, tree, unpack(args))
                 if ret == nil
                     info = debug.getinfo(compile_action, "S")
                     filename = Source\from_string(info.source).filename