language Error tracking

Close #3

7 files changed, 103 insertions, 11 deletions

diff --git a/core/base/init.moon b/core/base/init.moon
index 64b34f4..bb35140 100644
--- a/core/base/init.moon
+++ b/core/base/init.moon
@@ -12,6 +12,7 @@
 -- @see match
 -- @see Value
 -- @see Result
+-- @see Error
 
 import IO from require 'core.base.io'
 import Op from require 'core.base.op'
@@ -21,6 +22,7 @@ import Input from require 'core.base.input'
 import match from require 'core.base.match'
 import Value from require 'core.value'
 import Result from require 'core.result'
+import Error from require 'core.error'
 
 {
   :IO
@@ -31,5 +33,5 @@ import Result from require 'core.result'
   :match
 
   -- redundant exports, to keep anything an extension might need in one import
-  :Value, :Result
+  :Value, :Result, :Error
 }
diff --git a/core/base/match.moon b/core/base/match.moon
index a20bcdc..cb82ac4 100644
--- a/core/base/match.moon
+++ b/core/base/match.moon
@@ -2,6 +2,7 @@
 -- Utilities for matching `Result` types.
 --
 -- @module match
+import Error from require 'core.error'
 unpack or= table.unpack
 
 class Pattern
@@ -39,11 +40,11 @@ class Pattern
       matched = while @matches results[1]
         table.remove results, 1
 
-      assert @opt or #matched > 0, "expected at least one argument for spread"
+      assert @opt or #matched > 0, Error 'argument', "expected at least one argument for spread"
       matched
     else
       matches = @matches results[1]
-      assert @opt or matches, "couldn't match argument #{results[1]} as #{@}"
+      assert @opt or matches, Error 'argument', "argument #{results[1].value} incompatible with expected type #{@}"
       if matches then table.remove results, 1
 
   __tostring: =>
@@ -84,7 +85,7 @@ match = (pattern, inputs) ->
     pattern = rest
     Pattern pat
   values = [p\match inputs for p in *patterns]
-  assert #inputs == 0, "#{#inputs} extra arguments given!"
+  assert #inputs == 0, Error 'argument', "#{#inputs} extra arguments given!"
   values
 
 {
diff --git a/core/error.moon b/core/error.moon
new file mode 100644
index 0000000..a06c359
--- /dev/null
+++ b/core/error.moon
@@ -0,0 +1,85 @@
+----
+-- Language error and traceback.
+--
+-- @classmod Error
+class Error
+--- members
+-- @section members
+
+  --- append a traceback frame.
+  --
+  -- `where` should denote where the Error occured and fit grammatically to
+  -- complete the sentence `"{error} occured while {where}"`
+  --
+  -- @tparam string where
+  add_frame: (where) => @trace ..= "\n  while #{where}"
+
+  __tostring: => "#{@kind} error: #{@message}#{@detail}#{@trace}"
+
+--- static functions
+-- @section static
+
+  --- create a new Error.
+  --
+  -- `kind` should be one of:
+  --
+  -- - `'reference'`: error concerning symbol resolution
+  -- - `'argument'`: error concerning Op argument matching
+  -- - `'implementation'`: error in the Lua/MoonScript implementation of alive.
+  --   Should not occur in normal operation, and constitutes a bug.
+  --
+  -- @classmethod
+  -- @tparam string kind
+  -- @tparam string message
+  -- @tparam ?string detail
+  new: (@kind, @message, @detail) =>
+    @trace = ""
+
+  handler = (err) ->
+    if err.__class == Error
+      err
+    else
+      Error 'implementation', err, debug.traceback 'Lua error below:', 2
+  --- Wrap function errors in a traceback frame.
+  --
+  -- Execute `fn(...)`, and turn any error thrown as a result into an
+  -- `Error` instance, before re-throwing it.
+  --
+  -- When `Error` instances are caught, `frame` is added to the traceback.
+  -- All other error values are turned into `'implementation'` Errors.
+  --
+  -- @tparam string frame
+  -- @tparam function fn
+  @wrap: (frame, fn, ...) ->
+    results = { xpcall fn, handler, ... }
+    ok = table.remove results, 1
+    if ok
+      unpack results
+    else
+      error with results[1]
+        \add_frame frame
+
+  --- Capture and wrap function errors in traceback frame.
+  --
+  -- Execute `fn(...)`, and turn any error thrown as a result into an
+  -- `Error` instance, before re-throwing it.
+  --
+  -- When `Error` instances are caught, `frame` is added to the traceback.
+  -- All other error values are turned into `'implementation'` Errors.
+  --
+  -- @tparam string frame
+  -- @tparam function fn
+  -- @treturn boolean `ok` true if exeuction suceeded without errors
+  -- @treturn Error|any `error_or_results` the `Error` instance or results
+  @try: (frame, fn, ...) ->
+    results = { xpcall fn, handler, ... }
+    ok = table.remove results, 1
+    if ok
+      ok, unpack results
+    else
+      ok, with results[1]
+        \add_frame frame
+
+{
+  :Error
+}
diff --git a/core/init.moon b/core/init.moon
index a5e892d..00e3cd4 100644
--- a/core/init.moon
+++ b/core/init.moon
@@ -17,6 +17,7 @@ L or= setmetatable {}, __index: => ->
 import Value from require 'core.value'
 import Result from require 'core.result'
 import Scope from require 'core.scope'
+import Error from require 'core.error'
 import Registry, SimpleRegistry from require 'core.registry'
 import Tag from require 'core.tag'
 
@@ -35,6 +36,7 @@ globals = Scope.from_table require 'core.builtin'
 -- @tfield Cell Cell
 -- @tfield RootCell RootCell
 -- @tfield Scope Scope
+-- @tfield Error Error
 -- @tfield Registry Registry
 -- @tfield Tag Tag
 -- @tfield Scope globals global definitons
@@ -42,7 +44,7 @@ globals = Scope.from_table require 'core.builtin'
 {
   :Value, :Result
   :Cell, :RootCell
-  :Scope
+  :Scope, :Error
 
   :Registry, :SimpleRegistry, :Tag
 
diff --git a/core/invoke.moon b/core/invoke.moon
index 736f284..97d3949 100644
--- a/core/invoke.moon
+++ b/core/invoke.moon
@@ -6,6 +6,7 @@ import Value from require 'core.value'
 import Result from require 'core.result'
 import Action from require 'core.base'
 import Scope from require 'core.scope'
+import Error from require 'core.error'
 
 --- `Action` implementation that invokes an `Op`.
 --
@@ -40,7 +41,7 @@ class op_invoke extends Action
   -- @treturn Result
   eval: (scope, tail) =>
     children = [L\push expr\eval, scope for expr in *tail]
-    @op\setup [result for result in *children], scope
+    Error.wrap "invoking #{@op}#{@tag}", @op\setup, [result for result in *children], scope
 
     any_dirty = false
     for input in @op\all_inputs!
@@ -91,8 +92,8 @@ class fn_invoke extends Action
       with L\push tail[i]\eval, outer_scope
         fn_scope\set name, \make_ref!
 
-    body = body\clone @tag
-    result = body\eval fn_scope
+    clone = body\clone @tag
+    result = Error.wrap "invoking function #{body.tag} at #{@tag}", clone\eval, fn_scope
 
     table.insert children, result
     Result :children, value: result.value
diff --git a/core/value.moon b/core/value.moon
index bda6127..7f5a93d 100644
--- a/core/value.moon
+++ b/core/value.moon
@@ -3,6 +3,7 @@
 --
 -- @classmod Value
 import Result from require 'core.result'
+import Error from require 'core.error'
 import scope, base, registry from require 'core.cycle'
 
 ancestor = (klass) ->
@@ -107,7 +108,7 @@ class Value
       when 'num', 'str'
         Result value: @
       when 'sym'
-        assert (scope\get @value), "undefined reference to symbol '#{@value}'"
+        assert (scope\get @value), Error 'reference', "undefined symbol '#{@value}'"
       else
         error "cannot evaluate #{@}"
 
diff --git a/core/version.moon b/core/version.moon
index e5a965c..af97600 100644
--- a/core/version.moon
+++ b/core/version.moon
@@ -12,8 +12,8 @@
 -- @tfield string web the repo web URL
 {
   tag: "v0.0"
-  rev_short: "23f893a"
-  rev_long: "23f893a1303b35e11d7103d892c40b7e8d209a06"
+  rev_short: "662def4"
+  rev_long: "662def4ef082412147ae8126e80065d245f4b426"
   repo: "https://github.com/s-ol/alivecoding.git"
   web: "https://github.com/s-ol/alivecoding/tree/v0.0"
 }