Tidying up exceptions and error reporting. Also simplified the grammar a

tiny bit.

1 files changed, 30 insertions, 12 deletions

diff --git a/core/control_flow.nom b/core/control_flow.nom
index f5c61e3..73a0f43 100644
--- a/core/control_flow.nom
+++ b/core/control_flow.nom
@@ -49,13 +49,13 @@ immediately
                 To see why this is necessary consider: (random()<.5 and false or 99)
             return
                 Lua value ".."
-                    (function()
+                    ((function()
                         if \(%condition as lua expr) then
                             return \(%when_true_expr as lua expr)
                         else
                             return \(%when_false_expr as lua expr)
                         end
-                    end)()
+                    end)())
 
 # GOTOs
 immediately
@@ -361,31 +361,46 @@ immediately
 # Try/except
 immediately
     compile [..]
-        try %action and if it succeeds %success or if it barfs %fallback
-        try %action and if it barfs %fallback or if it succeeds %success
+        try %action and if it succeeds %success or if it barfs %msg %fallback
+        try %action and if it barfs %msg %fallback or if it succeeds %success
     ..to
         Lua ".."
             do
                 local fell_through = false
-                local ok, ret = pcall(function()
+                local err, erred = nil, false
+                local ok, ret = xpcall(function()
                     \(%action as lua statements)
                     fell_through = true
+                end, function(\(%msg as lua expr))
+                    local ok, ret = pcall(function()
+                        \(%fallback as lua statements)
+                    end)
+                    if not ok then err, erred = ret, true end
                 end)
                 if ok then
                     \(%success as lua statements)
                     if not fell_through then
                         return ret
                     end
-                else
-                    \(%fallback as lua statements)
+                elseif erred then
+                    error(err, 0)
                 end
             end
+immediately
+    parse [..]
+        try %action and if it succeeds %success or if it barfs %fallback
+        try %action and if it barfs %fallback or if it succeeds %success
+    ..as: try %action and if it succeeds %success or if it barfs (=lua "") %fallback
+immediately
     parse [try %action] as
         try %action and if it succeeds: do nothing
         ..or if it barfs: do nothing
     parse [try %action and if it barfs %fallback] as
         try %action and if it succeeds: do nothing
         ..or if it barfs %fallback
+    parse [try %action and if it barfs %msg %fallback] as
+        try %action and if it succeeds: do nothing
+        ..or if it barfs %msg %fallback
     parse [try %action and if it succeeds %success] as
         try %action and if it succeeds %success or if it barfs: do nothing
 
@@ -406,17 +421,20 @@ immediately
                     fell_through = true
                 end)
                 \(%final_action as lua statements)
-                if not ok then error(ret) end
+                if not ok then error(ret, 0) end
                 if not fell_through then return ret end
             end
 
 # Inline thunk:
 immediately
     compile [result of %body] to
-        Lua value ".."
-            (function()
-                \(%body as lua statements)
-            end)()
+        %body <- (%body as lua statements)
+        declare locals in %body
+        return
+            Lua value ".."
+                ((function()
+                    \%body
+                end)())
 
 # Coroutines:
 immediately