Declarations-to-GlobalUsingTXL

TXL solution to TIL Chairmarks #2.3, Declarations-to-global, move all declarations from any nesting level to the global scope.

-- JamesCordy - 02 Nov 2005

File "TILtoglobal.Txl"

% TXL transformation to move all declarations in a TIL program to the 
% beginning of the program, making their meaning explicit

% Jim Cordy, October 2005

% Based on the TIL base grammar
include "TIL.Grm"

% Preserve comments, we're probably going to maintain the result
include "TILCommentOverrides.Grm"

% Transformation rule to move all declarations to the beginning of the program -
% does it the easy obvious way, extracting them all, deleting them all, then
% putting the extracted ones first.  

function main
    % This is a function transformer, so it applies only once 
    replace [program]
        Program [statement*]

    % Use the type extractor to get all statements as a flat sequence,
    % then filter for declarations only
    construct Declarations [statement*]
            _ [^ Program] [removeNonDeclarations]

    % Make a copy of the program with all declarations removed
    construct ProgramSansDeclarations [statement*]
            Program [removeDeclarations]

    % The result is a program consisting of the sequence of all the
    % declarations concatenated with the original program without declarations
    by
            Declarations [. ProgramSansDeclarations]
end function

rule removeDeclarations
    % Rule to remove every declaration at every level from statements
    replace [statement*]
        Declaration [declaration]
        FollowingStatements [statement*]
    by
        FollowingStatements
end rule

rule removeNonDeclarations
    % Rule to remove all statements that are not declarations from statements
    replace [statement*]
        NonDeclaration [statement]
        FollowingStatements [statement*]

    % Check that the statement isn't a declaration 
    deconstruct not NonDeclaration
            _ [declaration]

    % If so, take it out
    by
        FollowingStatements
end rule

Example run: "vareg.til" is a meaningless little program with lots of data dependencies for demonstration purposes.

<linux> cat vareg.til
var d;
d := 17;
var r;
r := 5;
var y;
read y;
var z;
read z;
while y != 0 do
    var x;
    x := y + z;
    var a;
    a := 3;
    var j;
    j := 1;
    var b;
    while j != 100 do
        var k;
        k := a + z;
        b := j * z;
        d := (y + z) * d;
        var e;
        e := (x + z) * r;
        j := j + 1;
    end
    var c;
    c := a + y;
    var m;
    m := y * b;
    var n;
    n := r * y;
    write n;
    y := y - 1;
end
<linux> txl vareg.til TILtoglobal.Txl
TXL v10.4a (15.6.05) (c)1988-2005 Queen's University at Kingston
Compiling TILtoglobal.Txl ... 
Parsing vareg.til ...
Transforming ...
var d;
var r;
var y;
var z;
var x;
var a;
var j;
var b;
var k;
var e;
var c;
var m;
var n;
d := 17;
r := 5;
read y;
read z;
while y != 0 do
    x := y + z;
    a := 3;
    j := 1;
    while j != 100 do
        k := a + z;
        b := j * z;
        d := (y + z) * d;
        e := (x + z) * r;
        j := j + 1;
    end
    c := a + y;
    m := y * b;
    n := r * y;
    write n;
    y := y - 1;
end
<linux>