TILParser Using TXL
Software Transformation Systems
TXL solution for TIL Chairmarks #1: A parser for the Tiny Imperative Language (TIL) implemented in TXL.
This is the entire solution, run using the command "txl program.til TILparser.Txl" no other libraries, support modules or data files are needed. See below for an example run.
This version accepts but does not preserve comments, which is the default in TXL. For a pretty-printer for TIL see TIL Pretty Printer Using TXL.
-- JamesCordy - 17 Aug 2005 (revised JamesCordy - 02 Nov 2005)
File "TILparser.Txl"
% TXL parser / pretty-printer for Tiny Imperative Language
% Jim Cordy, April 2005
% All TXL parsers are automatically also pretty-printers if the
% grammar includes the optional formatting cues, as in this case
% Use the TIL grammar shown below
include "TIL.Grm"
% No need to do anything except recognize the input, since the grammar
% includes the output formatting cues
function main
match [program]
_ [program]
end function
File "TIL.Grm"
% TXL grammar for Tiny Imperative Language
% Jim Cordy, April 2005
% Note that all quoting, as in 'if, is not required,
% rather an optional coding convention used by TXL programmers
% Formatting cues, such as [NL] on the right, are optional output formatting
% suggestions and have no input parse meaning
% From the spec, it is not clear if TIL should be priority expression parsed or not,
% so this grammar provides both, controlled by this switch
% #define PRIORITY
% Keywords of TIL, assuming TIL is a reserved-word language
% If not, remove this section
keys
var if then else while do for read write
end keys
% Compound tokens to be recognized as a single lexical unit
compounds
:= !=
end compounds
% Commenting convention for TIL, assuming it has one
comments
//
end comments
% Direct TXL encoding of the TIL specification grammar -
% I don't think any explantions are needed from here on
% [NL], [IN] and [EX] on the right are optional pretty-printing cues
define program
[statement*]
end define
define statement
[declaration]
| [assignment_statement]
| [if_statement]
| [while_statement]
| [for_statement]
| [read_statement]
| [write_statement]
end define
% Untyped variables
define declaration
'var [id] ; [NL]
end define
define assignment_statement
[id] := [expression] ; [NL]
end define
define if_statement
'if [expression] 'then [IN][NL]
[statement*] [EX]
[opt else_statement]
'end [NL]
end define
define else_statement
'else [IN][NL]
[statement*] [EX]
end define
% While loop
define while_statement
'while [expression] 'do [IN][NL]
[statement*] [EX]
'end [NL]
end define
% Declaring for
define for_statement
'for [id] := [expression] 'to [expression] 'do [IN][NL]
[statement*] [EX]
'end [NL]
end define
define read_statement
'read [id] ; [NL]
end define
define write_statement
'write [expression] ; [NL]
end define
#if not PRIORITY then
% Simple nonpriority expression grammar, as specified
define expression
[primary]
| [expression] [op] [expression]
end define
define op
= | !=
| + | -
| * | /
end define
#else PRIORITY
% Alternative traditional priority expression grammar
define expression
[term]
| [expression] [eqop] [term]
end define
define eqop
= | !=
end define
define term
[factor]
| [term] [addop] [factor]
end define
define addop
+ | -
end define
define factor
[primary]
| [factor] [mulop] [primary]
end define
define mulop
* | /
end define
#end if PRIORITY
define primary
[id]
| [literal]
| ( [expression] )
end define
define literal
[integernumber]
| [stringlit]
end define
Example run:
(Note comments are accepted in input and removed in output; see TIL Pretty Printer Using TXL for a comment-preserving version.)
<linux> cat factors.til
// Factor an input number
var n; write "Input n please"; read n;
write
"The factors of n are"; var f; f := 2;
while n != 1 do while (n / f) * f = n do
// Got one - print it!
write f; n := n / f;
end
f := f + 1;
end
<linux> txl factors.til TILparser.Txl
TXL v10.4a (15.6.05) (c)1988-2005 Queen's University at Kingston
Compiling TILparser.Txl ...
Parsing factors.til ...
Transforming ...
var n;
write "Input n please";
read n;
write "The factors of n are";
var f;
f := 2;
while n != 1 do
while (n / f) * f = n do
write f;
n := n / f;
end
f := f + 1;
end
<linux>
Example run with XML parse tree output:
<linux> txl factors.til TILparser.Txl -xml
TXL v10.4a (15.6.05) (c)1988-2005 Queen's University at Kingston
Compiling TILparser.Txl ...
Parsing factors.til ...
Transforming ...
<program>
<repeat_statement>
<statement><declaration> var
<id>n</id> ;
</declaration>
</statement>
<statement><write_statement> write
<expression>
<primary><literal><stringlit>"Input n please"</stringlit></literal></primary>
</expression> ;
</write_statement>
</statement>
<statement><read_statement> read
<id>n</id> ;
</read_statement>
</statement>
<statement><write_statement> write
<expression>
<primary><literal><stringlit>"The factors of n are"</stringlit></literal></primary>
</expression> ;
</write_statement>
</statement>
<statement><declaration> var
<id>f</id> ;
</declaration>
</statement>
<statement><assignment_statement>
<id>f</id> :=
<expression>
<primary><literal><integernumber>2</integernumber></literal></primary>
</expression> ;
</assignment_statement>
</statement>
<statement><while_statement> while
<expression>
<expression><primary><id>n</id></primary></expression>
<op>!=</op>
<expression>
<primary><literal><integernumber>1</integernumber></literal></primary>
</expression>
</expression> do
<repeat_statement>
<statement><while_statement> while
<expression>
<expression>
<expression><primary> (
<expression>
<expression><primary><id>n</id></primary></expression>
<op>/</op>
<expression><primary><id>f</id></primary></expression>
</expression> )
</primary>
</expression>
<op>*</op>
<expression><primary><id>f</id></primary></expression>
</expression>
<op>=</op>
<expression><primary><id>n</id></primary></expression>
</expression> do
<repeat_statement>
<statement><write_statement> write
<expression><primary><id>f</id></primary></expression> ;
</write_statement>
</statement>
<statement><assignment_statement>
<id>n</id> :=
<expression>
<expression><primary><id>n</id></primary></expression>
<op>/</op>
<expression><primary><id>f</id></primary></expression>
</expression> ;
</assignment_statement>
</statement>
</repeat_statement> end
</while_statement>
</statement>
<statement><assignment_statement>
<id>f</id> :=
<expression>
<expression><primary><id>f</id></primary></expression>
<op>+</op>
<expression>
<primary><literal><integernumber>1</integernumber></literal></primary>
</expression>
</expression> ;
</assignment_statement>
</statement>
</repeat_statement> end
</while_statement>
</statement>
</repeat_statement>
</program>
<linux>