diff options
| -rw-r--r-- | generic/tclBasic.c | 45 |
1 files changed, 21 insertions, 24 deletions
diff --git a/generic/tclBasic.c b/generic/tclBasic.c index 361ed49..e92e8e9 100644 --- a/generic/tclBasic.c +++ b/generic/tclBasic.c @@ -4142,8 +4142,9 @@ TclNREvalObjv( /* * data[1] stores a marker for use by tailcalls; it will be set to 1 by - * command redirectors (imports, alias, ensembles) so that tailcalls - * finishes the source command and not just the target. + * command redirectors (imports, alias, ensembles) so that tailcall skips + * this callback (that marks the end of the target command) and goes back + * to the end of the source command. */ if (iPtr->deferredCallbacks) { @@ -4406,7 +4407,7 @@ NRCommand( iPtr->numLevels--; /* - * If there is a tailcall, schedule it + * If there is a tailcall, schedule it next */ if (data[1] && (data[1] != INT2PTR(1))) { @@ -8170,27 +8171,24 @@ Tcl_NRCmdSwap( } /***************************************************************************** - * Stuff for tailcalls + * Tailcall related code ***************************************************************************** * - * Just to show that IT CAN BE DONE! The precise semantics are not simple, - * require more thought. Possibly need a new Tcl return code to do it right? - * Questions include: - * (1) How is the objc/objv tailcall to be run? My current thinking is that - * it should essentially be - * [tailcall a b c] <=> [uplevel 1 [list a b c]] - * with two caveats - * (a) the current frame is dropped first, after running all pending - * cleanup tasks and saving its namespace - * (b) 'a' is looked up in the returning frame's namespace, but the - * command is run in the context to which we are returning - * Current implementation does this if [tailcall] is called from within - * a proc, errors otherwise. - * (2) Should a tailcall bypass [catch] in the returning frame? Current - * implementation does not (or does it? Changed, test!) - it causes an - * error. - * - * FIXME NRE! + * The steps of the tailcall dance are as follows: + * + * 1. when [tailcall] is invoked, it stores the corresponding callback in + * the current CallFrame and returns TCL_RETURN + * 2. when the CallFrame is popped, it calls TclSetTailcall to store the + * callback in the proper NRCommand callback - the spot where the command + * that pushed the CallFrame is completely cleaned up + * 3. The NRCommand schedules the tailcall callback to run immediately after + * NRCommand returns + * + * One delicate point is to properly define the NRCommand where the tailcall + * will execute. There are functions whose purpose is to help define the + * precise spot: TclMarkTailcall ("this is the spot") and TclSkipTailcall + * ("skip the next command: we are redirecting to it, tailcalls should run + * after WE return"), TclPushTailcallPoint (special for OO). */ void @@ -8282,8 +8280,7 @@ TclNRTailcallObjCmd( /* * Create the callback to actually evaluate the tailcalled * command, then set it in the varFrame so that PopCallFrame can use it - * at the proper time. Being lazy: exploit the TclNRAddCallBack macro to - * build the callback. + * at the proper time. */ if (objc > 1) { |