Stratego/XT 0.17

Stratego -- Strategies for Program Transformation

Stratego/XT 0.17 - released July 2009

Known issues

  • On 64 bit systems, parsing using SGLR (which is used in many Stratego programs) can result in SEGV due to limited stack size. This can be solved by executing ulimit -s unlimited, or with any bigger stack size than the current one.
  • The ATerm library needs this patch to work.


See the installation instructions if you are not familiar with the standard installation procedure of tarballs or RPMs.

Source tar.gz

SuSE Linux RPM

SuSE 11.0:

SuSE 10.3:

Fedora Core RPM

Fedora Core 11:

Fedora Core 10:

Fedora Core 9:

Fedora Core 5:

Debian DEB

Debian 5.0:

Debian 4.0:

Ubuntu DEB

Ubuntu 9.04:

Ubuntu 8.10:

Ubuntu 8.04:

Microsoft Windows Cygwin binaries

  • The *-cygwin.tar.gz files contain a file README with installation instructions.

Mac OS X binaries

  • The *-macosx.tar.gz files contain a file README with installation instructions.

Nix Package

One-click installation using Nix, open with nix-install-package


Stratego/XT Manual

The Stratego/XT Manual is a series of three books: a tutorial, a series of examples, and a reference manual with the finer details of the language and tools. The manual is available online and can be downloaded for offline use.

Warning: this manual is specific for Stratego/XT 0.17 and will not be extended. The latest version of the manual, available at at the documentation page, might be more extensive, but might also cover features that were not yet available in Stratego/XT 0.17.

Stratego/XT API Documentation

Online API documentation:

Download API documentation for local and offline use:


Stratego/XT is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This software is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.


Despite the disclaimer above we do our best to help users of Stratego/XT. Subscribe to the Stratego mailing lists, in particular the stratego-announce and stratego mailing lists to get announcements of new releases and ask questions about usage of the languages and tools. Also we're interested to know what people are using Stratego/XT for and how it might be improved, so feel free to drop us a line.

Stratego/XT 0.17 - released July 2009

Summary of Changes

Stratego/XT 0.17 introduces major improvements across the board, including language additions, a new compiler library, numerous improvements to the compiler, significant changes to the library handling, new libraries for parsing, pretty printing and term validation, 64-bit support, stack traces and more.

For this release, over 200 outstanding issues have been addressed, much thanks to the efforts of external bug reporters and contributors.

The manual has been updated to reflect the changes made to the language and libraries, and the new libraries come with up-to-date source code documentation.

Stratego in Print

M. Bravenboer, K. T. Kalleberg, R. Vermaas, and E. Visser. Stratego/XT 0.17. A Language and Toolset for Program Transformation. Science of Computer Programming, 2008. Special issue on Experimental Systems and Tools,

Stratego Compiler

Standard C: Dropped GCC's nested functions

The backend has been changed so that the GCC-specific nested functions feature is no longer required. This makes the C-code a lot more portable across GCC-supported platforms, since nested functions are not reliably supported on all architectures, notably not on MIPS and OSX/Intel. Furthermore, this allows Stratego to use other C compilers for than GCC for the generation of platform-specific binary code.

  • [STR-697] - Standalone strc; allow users to override --cc and ---ld
  • [STR-119] - Replace GCC nested functions by stack-allocated closures as structs

Stack traces on "rewriting failed"

The compiler backend and supporting runtime code have been modified to provide full stack traces for the dreaded "rewriting failed" situations.

Consider the following program:

  main = foo

  foo = bar

  bar = fap ; zap

  fap = id

  zap = fail 

When executed, it will print:

prog: rewriting failed, trace:

This also works when you use io-wrap and friends, but there are some caveats:

  • Only code compiled with the new compiler will show up in the stack trace: if you call old libraries, stack frames for those strategies will be invisble.

  • let blocks and other reasons for lifting will show up as lifted_X frames.

A tiny set of stack introspection strategies for debugging purposes has also been introduced.

A new "with" construct for rewrite rules

A new with construct has been added for rewrite rules, which makes use of the stack tracing feature above. A with clause works much like a regular where clause, and can for example be used to assign variables for use in the right-hand side of a rule:

    |[ e1 + e2 ]| -> |[ x_add(e1, e2) ]|
      <typeof> e1 => Int()
    ; <typeof> e2 => Int()
      x_add := <new-add-operation> (e1, e2)

However, unlike the where clause, its operations are not allowed to fail, or a run-time error will be reported with a stack trace. Thus, this addition allows Stratego programmers to explicitly distinguish between conditions of a rule (the where clause) and operations that must always succeed (the with clause). This helps in readability and in debugging errors in rewrite rules. Any failures inside a with clause are considered programmer errors: the contract specified by the with clause is then not satisfied (for example, a rule may require some dynamic rule to be defined). By immediately reporting such errors, this feature allows them to be quickly identified, avoiding problems that are only detected in the result of a transformation (e.g., after some rules did not fire in a topdown(try(s)) strategy).

For every rewrite rule, an unrestricted number of with and where clauses can be used. In strategies, with can be used as a strategy invocation, similar to where (e.g., with(<may-not-fail> t)).

Compiler library

The compiler has been librarified. Program analysis and transformation tools which work on Stratego code may now be based on the Stratego compiler library. The intent is to make meta-programming with Stratego a lot easier and speedup the Stratego compiler.

  • [STR-311] - strc-lib : a library for compilation (meta-programming) Stratego

Stratego Language

Assignment operator

An assignment operator has been added to the language as a more attractive syntax for the common pattern s => t. In the assignment operator, the variable name is now before the right-hand side. Also, the right-hand side is a term pattern.

  get-signature(|file) :
    Method(_, returntype, name, types, _, _) -> 
    MethodSignature(cn, returntype, name, types)
      cn := <get-classname> file

This used to be written as:

  <get-classname> file => cn

Note that this is a purely syntactic change: the variable can only be assigned to once.

Dynamic rules

Improved flow-sensitive transformations

Thanks to Bogdan Dumitriu, the dynamic rule facility of Stratego has been extended to deal with additional control flow constructs, including break, break to label, continue and exceptions (try-catch-finally). Some of the dynamic rule strategies, such as dr-fix-and-intersect and dr-fix-and-union have been extended to work with labels, and new dynamic rule prefixes break- and break-to-label- are introduced.

A presentation from Stratego User Days 2006 provides a high-level walk-through.

Scoped global variables

Stratego now supports scoped global variables. In the context of a dynamic rules section one can now write

    rules( Foo := <compute> )
which abbreviates the following commonly used programming pattern:
    x := <compute>
    ; rules( Foo : _ -> x )
The value bound in the assignment can be retrieved by the application <Foo>. The usual scoping features of dynamic rules apply to global variable as well. For more information see this blog.

Chained dynamic rules

A useful extension to the standard strategies generated for invoking dynamic rules such as bagof-Foo, once-Foo, etc.

The idea is that it is in general useful to apply a sequence of dynamic rules, but not produce all possible results, but chain each result to the next dynamic rule invocation.

Suppose that you have two dynamic rules defined:

 Foo : x -> (1, x)
 Foo : x -> (2, x)

With these two rules defined, applying 0 will result in (2, (1, 0)).

In this way, you can apply a series of dynamic rules to a term. Note that you can achieve this with repeat(once-Foo) as well, but once-Foo will remove the rule from the environment, which is not always desirable.

While chain-Foo only applies the rules visible in the current scope, bigchain-Foo applies the rules from all scopes.

External Constructor Declarations

  • [STR-672]: fix multiple external definitions problems

While proper strategy definitions that are imported as externals are not exported as externals from a library (as per August 2006), constructors imported by a library, were also exported by that library. This caused congruences to be regenerated, possibly not in that same library, but in a library one step further in the import chain. Thus, the external definitions for congruences from an imported library, prevented generation of new congruences. However, since imported external definitions are not exported, the next library does not see those congruence definitions, and will re-generate them; giving rise to a warning when the external definition for this new congruence is imported in another application or library.

To solve this issue constructors are now treated in the same way as strategy definitions.

There is now a notion of "external" constructor declarations. Syntax:

  external Foo : A * B -> C

These external constructor declarations are exported by a library along with the external definitions for the strategies in the library. Thus, importing libraries and programs can use these constructors in rules and strategies.

However, external constructors are not exported from an importing library. Just like external definitions are not exported from an importing library. This entails that a third library that imports the second, does not get the constructor declarations of the first. In order to use those, the first library needs to be imported explicitly. Here is an example:

Library A
module A
    Foo : A
module libA
    external Foo : A

Library B
module B
  imports libA
    bar = !Foo()
    // constructor Foo is available through libA import
module libB
    external bar
    // only strategy bar is exported, not constructor Foo

Library or Application C
module C
  imports libB
    baz = !Foo(); ...; bar
          // error! libB does not export constructor Foo

Library or Application C // corrected
module C
  imports libB libA
    baz = !Foo(); ...; bar
    // Foo is imported through libA

This change may break existing code; explicit imports of indirectly imported libraries are needed. In practice, the change had a minimal impact on the code in Stratego/XT and derived projects.

Rule syntax in let

The let construct now allows the defition of rules in addition to strategies:

  let R : p1 -> p2

Import ATerm from file

A new language construct called import-term was added which allows the embedding of terms (data) directly into the program.

  get-pp-table = import-term(pptable.trm)

This removes the need for external data files, such as parse and pretty-print tables. The resulting executable is self-contained, thus making deployment of your program transformation tools easier.

  • [STR-577] - Stratego: support import of an ATerm from a file

Stratego Libraries

A new discipline for library naming and usage is introduces in 0.17. The standard library is now named libstratego-lib, whereas the XTC library is named libstratego-xtc. Additional libraries have been added for parsing, pretty printing and term validation, see below.

Migrating from XTC to libraries

To avoid the term serialization paid when composing transformation pipelines using XTC, the compiler and all supporting tools have been rearchitected as libraries in addition to the familiar XTC components.

For Stratego/XT users, the most significant change is that the SGLR parser, the various RTG tools and the GPP tools are now available as libraries, respectively named libstratego-sglr, libstratego-rtg and libstratego-gpp.

The librarification allows parse tables to be loaded once, at startup, and used repeatedly when multiple files must be parsed (when using XTC, the parse table is loaded by the sglr child process every time a file must be parsed).

Consider the following program:

module foo
  main =
    tbl := <import-term(Exp.tbl); open-parse-table>
    ; <parse-string(|tbl)> "a+b"

It assumes the existence of a parse table (Exp.tbl). This table is included into the program using the import-term construct (introduced above). The call to open-parse-table will register the parse table with the libstratego-sglr library, and subsequent calls to parse-string will not need to reload the parse table.

Compiling and executing the program:

$ strc -i foo.str $(strcflags stratego-lib stratego-sglr)
$ ./foo 

The resulting program foo is now fully self-contained. It does not need the Exp.tbl file to execute.

API documentation for the Stratego Libraries is available from the Documentation page on the Stratego/XT website.


The new tool strcflags makes it no longer necessary to know all the details of how to invoke the Stratego compiler when you're using a certain library. Given the name of a package or Stratego library, the tool returns the flags (such as include paths) for strc.


$ strc -i foo.str $(strcflags stratego-lib)

You can also specify multiple packages. For example, if you're using java-front, then you are usually using the Stratego library as well.

$ strc -i foo.str $(strcflags stratego-lib java-front)

The tool strcflags is a simple wrapper around the tool pkg-config, which we are using for configuring Stratego/XT packages when building packages from source.

To support strcflags with your own packages, add a declaration of a variable strcflags to the pkg-config .pc files.

Easy library creation

Creating libraries using the Stratego compiler has never been easier. By using the --library option to the compiler, all necessary library files will be created.

$ strc -i foo.str --library

The resulting output includes static and dynamic libraries, as well as libtool support files:

libfoo.a  libfoo.c  libfoo.lo  libfoo.o  libfoo.rtree 

This option is intended for creating libraries that are not part of an autoconf/automake package, similar to invoking strc to compile a program all the way to an executable.


This release brings about major improvements to the deployment capabilities of Stratego/XT.

Standards-compliant libraries

The Stratego libraries expose various features from the underlying platform Stratego/XT executes on. In 0.17, the library has been refactored so that the dependence on platforms is clearer, and this gives rise to several variants of the library, including one for C99, POSIX and one for POSIX+XSI. The great majority of Stratego/XT programs, use the high-level strategies for file and term I/O, and these programs will be unaffected.

The main benefit of this change is that we can now build all the Stratego libraries on platforms that only support functions from standard C99 (i.e. not full POSIX). This enables the deployment of Stratego applications on such platforms. Some strategies from the Stratego library are only available in the POSIX and POSIX+XSI extensions. The name of the modules defining these strategies reflect this.

  • [STR-613] - Stratego library: Allow creation of library for specific standard (C99, POSIX, POSIX XSI)

Native Windows Support (MinGW)

Stratego/XT now supports compiling natively on Microsoft Windows using MinGW. This results in a smaller footprint because of significantly fewer and smaller dependencies as compared with Cygwin.

Binaries created for MinGW can be deployed to Microsoft Windows users without any dependencies.

For this purpose, the stratego-libraries package is also available separately from Stratego/XT as source tarball and native Microsoft Windows binaries. If you already have Stratego/XT, then there is no need to install the stratego-libraries.

OSX support

Stratego/XT 0.17 now fully supports OSX on PowerPC as well as Intel CPUs.

x86-64 support

Thanks to patches from Eelco Dolstra, the ATerm library now supports 64-bit machines, and the final blocker preventing Stratego/XT running on 64-bit is now removed. This means 64-bit support is finally here. Binary packages for 64-bit Linux distributions are provided for your convenience.

Detailed List of Issues

The full list of issues closed in this release is available at:

Download and Installation

The release page contains the source distributions, binary RPMs, and detailed instructions on how to install the distributions:

Bugs and Known Problems

See our issue tracking systems for reports about (open) bugs:

Please report any problems with installation or bugs in the implementation to our issue tracking system. Please check the existing issues to see if a report about the problem was already submitted.


Developments, bug reports, and beta tests carried out by

  • Sigoure Benoit
  • Eric Bouwers
  • Martin Bravenboer
  • Arthur van Dam
  • Valentin David
  • Eelco Dolstra
  • Bogdan Dumitriu
  • Karl Trygve Kalleberg
  • Lennart Kats
  • Nicolas Pierron
  • Zef Hemel
  • Rob Vermaas
  • Eelco Visser