GPS Oct 19, 2003 - I've been thinking about how to build a Tcl compiler that allows for efficiently storing the compiled structure to the disk and also provides fast execution. I think this might work.
The goal of this compiler would be to provide a fast means of evaluating commands in a stored structure.
Rather than using a parse-tree a flat array of Tcl_Objs is used with an ordered list for execution. A LIFO stack is used to find the proper order of execution at compile time.
I propose the functions Tcl_Compile() and Tcl_Run() for dealing with these data structures.
Consider the command:
set v [foo bar [set bar 20] [baz $bar]]
In that example we first create an array of Tcl_Objs. The first element will be for a result of set v ...
[0 RESULT] [1 set]
We push the index of the set command, which in this case is 1.
LIFO stack[] = 1
We continue down the line adding objects for strings until we reach another branch.
[0 RESULT] [1 set] [2 v] [3 RESULT]
Now we are at a branch, where we have foo bar [set bar 20 [baz $bar]
We append another object for the foo command and push the index of the object, which in this case is 4.
[0 RESULT] [1 set] [2 v] [3 RESULT] [4 foo] [5 bar] LIFO stack[] = 1 4
Now we are at another branch for set bar 20 baz $bar
We append a RESULT object and push an index for the set object.
[0 RESULT] [1 set] [2 v] [3 RESULT] [4 foo] [5 bar] [6 RESULT] [7 set] [8 bar] [9 20] LIFO stack[] = 1 4 7
9 was the end of a command (]), so we pop one item off of the LIFO into our order list:
order list = 7
Now we just have the baz $bar to finish in a similar manner. We push the index of baz $bar's baz onto the LIFO and we end up with:
LIFO stack[] = 1 4 11 [0 RESULT] [1 set] [2 v] [3 RESULT] [4 foo] [5 bar] [6 RESULT] [7 set] [8 bar] [
9 20] 10 RESULT 11 baz 12 $bar 13 END OF ALL
The end of the command baz $bar is reached so we pop another item off the stack into our order list.
order list = 7 11
The end of the foo ... command is reached so we pop another and get:
order list = 7 11 4
and so forth until the command is complete
our order is: 7 11 4 1
Compare that order to these and you will see that it's the proper result:
0 RESULT 1 set 2 v 3 RESULT 4 foo 5 bar 6 RESULT 7 set 8 bar 9 20 10 RESULT 11 baz 12 $bar 13 END OF ALL
One aspect which we haven't discussed is result transfer. Each command copies its result to the object behind its beginning. This makes it so that each command result works properly.
This approach also allows us to write the Tcl_Obj structures to the disk more easily, and unlike a parse-tree it doesn't require many little mallocs, frees and evaluation at each branch.