StrategoXT 0.9.4 -- released January 22, 2004

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License

StrategoXT 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.

Summary of Changes

  • External definitions for separate compilation
  • Parsing programs with concrete syntax
  • Improvements in the run-time system
  • Injections in signatures
  • Extend dynamic rules
  • Drastic reduction of resources in run-time system
  • Upgrading pretty-print tables
  • Lots of improvements and fixes

Separate Compilation

The Stratego compiler is a whole program compiler. This entails that all imported modules are included into a single program, which is then compiled. The advantage is that the compiler has complete knowledge of all definitions in the program. The disadvantage is that compilation of library modules is repeated for each program, which makes compilation slow. To improve on this situation this release introduces an extension of Stratego with external definitions, which enables separate compilation. The separate compilation scheme is not per module; rather a module and all modules that it imports can be made available as a library. It is up to the programmer to determine the boundary between library and application. The feature is available in this release, but is still experimental.

External Definitions

External definitions are definitions of the form 'external f(as1|as2)' or 'external f(as1|as2) = s' and indicate a strategy that is implemented externally. It can be compiled with the normal calling convention for strategies and will be renamed in the same way to f_n_m with n the number of strategy parameters and m the number of term parameters. The second form allows the specification of a strategy body for the definition. This can be used by the compiler to inline some applications of the strategy operator, but no implementation is generated for such definitions. External definitions cannot be extended.

External definitions generalize 'prim'itive strategies and can be used to implement separate compilation. That is, to implement an external definition f(as1|as2), the program should be linked with an object file which provides a function f_n_m with n = |as1| and m = |as2|. Such an object file can be produced from a program written directly in C, or can be generated from a Stratego program.

Library Generation

The Stratego Compiler strc can be used now to generate a library from a module file.str with the command 

  strc -i mod.str -c -o libmod.c --library

This produces three files:

  • libmod.c
  • libmod.str
  • libmod.rtree

The first is the C implementation of the closure of mod.str. It provides C functions for all user-defined strategies, and static C functions for strategies generated at compile-time. The last two are the concrete syntax and abstract syntax files for a Stratego module with external definitions for all strategies defined in mod.str and imported modules. It is now possible to import libmod in another Stratego program, instead of mod. Note that libmod.str is produced mainly for documentation, libmod.rtree should be used to import. This is done automatically by the compiler as long as the file is present.

Note that no modules from the 'library' should be imported in the program via another path. This will lead to doubly defined strategies; it is not allowed to extend external definitions.

The C program libmod.c can be compiled to an object file libmod.o and to a library liblibmod.a. This should be done in a makefile; strc does not deal with C compilation of libraries. Also strc does not find imported object libraries; these should be declared explicitly to the C compiler (for instance using the LDADD flag in a makefile). Static linking of the libraries thus produced may actually lead to larger executables since no unused-function-removal is performed on the library (for obvious reasons). Shared libraries are the solution here to save diskspace. This can be achieved by proper use of libtool in the buildenvironment; again strc does not provide support for this.

(Remark: the C compilation facility in strc is mainly intended for use by novices; any serious application of strc should be embedded in a proper build environment where C compilation is better left to that environment.)

The current version of strc does not produce implementations of definitions for inlining in the importing program. This is catered for in the implementation, though. Some more experience is needed with this feature before making it available.

Currently, no overlays are exported to the library module.

(Eelco Visser)

Other Language Extensions / Changes

Injections

An injection is a constructor declaration without constructor name. This can be useful for introducing shorter sort names. For example, 

  signature
    constructors
      FunDec : Id * FunArgs * Type * Exp -> Dec
             : String -> Id
             : List(FunArg) -> FunArgs

Injections are accepted syntactically, but since no typechecking is done (yet), they make no difference for compilation at the moment. However, the quality of (generated) signatures becomes much better by this feature.

(Martin Bravenboer)

Extend Rules

First implementation of 'extend rules' variant of dynamic rules. Defining a dynamic rule as 

  extend rules(
    A : lhs -> rhs where s
  )

creates a dynamic rule A, which as usual returns the rhs of the rule last created. In addition, a rule bagof-A is generated, which rewrites lhs to all rhss in the current scope, i.e., produces a list of all 'values' of lhs.

(Eelco Visser and Arthur van Dam)

Concrete-Syntax

Parsing Programs with Concrete-Syntax

Stratego supports definition of rewrite rules and strategies with concrete syntax of the object language. This feature is also useful for other languages. In the paper 'Retrofitting the AutoBayes Program Synthesis System with Concrete Syntax' it is shown how concrete syntax can be added to Prolog. (Implementation in prolog-tools package.)

Concrete-syntax is a new package in the StrategoXT bundle. Its purpose is to provide generic utilities for handling programs with concrete syntax for arbitrary meta-languages. So far it provides just the program parse-cs, which is an implementation of the generic architecture for parsing with concrete syntax outlined in the GPCE'02 paper 'Meta-Programming with Concrete Object Syntax'.

The program is parameterized with meta-data indicating components for various aspects such as parsing, exploding, desugaring, and pretty-printing. The meta data can be specified in a .meta file specific for a program to be parsed, or it can be associated with an extension and registered in an XTC repository.

For example, the following is the content of pl.meta, the meta-data for Prolog programs with embedded syntax. The assumption (in this example) is that syntax embeddings use a standard (ToTerm?) convention for indicating the boundary between meta- and object-syntax. 

  Meta([
    Syntax("Prolog"),
    ParseTable("Prolog.tbl"),
    Explode("prolog-explode"),
    PrettyPrintTable("Prolog-pretty.pp.af")
  ])

This information can be overridden in a file specific .meta file with the same extension. For example, the following indicates an embedding of ABIR in Prolog and a specific desugaring tool for this format: 

  Meta([
    Syntax("PrologABIR"),
    PostExplodeDesugar("abir-in-prolog-implode")
  ])

It overrides the syntax component, and adds a desugaring component.

In order to define such meta-data for a whole class of programs, it can be defined in a meta file associated with a new extension. For example, the following is the contents plabir.meta, which defines all meta-data for preprocessing Prolog with embedded ABIR in files with extension .plabir. 

  Meta([
    Syntax("PrologABIR"),
    Explode("prolog-explode"),
    PostExplodeDesugar("abir-in-prolog-implode"),
    PrettyPrintTable("Prolog-pretty.pp.af")
  ])

(Eelco Visser)

Transforming AsFix?

Parse trees produced by sglr are in the AsFix? format which contains all details concerning layout and the structure of lexical syntax. For some applications it is useful to apply transformations to this AsFix? format, rather than the imploded abstract syntax. While generic AsFix? transformations can be written quite compactly using abstract syntax (constructors app, prod, sort, etc), transformations which are specific for the object language become gruesome. The --asfix switch of the implode-asfix algorithm now indicates that AsFix? trees which occur within the concrete syntax quotes should not be imploded. Thus, it becomes possible to write transformations on AsFix? using concrete syntax. (Valentin David)

Run-Time System

Don't Reconstruct Identical Term on Traversal

Changed one-step traversal functions such that a new term is only built if there was an actual change to at least one of the sub-terms, thus avoiding unnecessary term construction. (Based on an idea by Eelco Dolstra.) A one off test on one program suggests that it makes no difference at all. But we should wait for results with more programs.

(Eelco Visser)

Jumpbuffer

Improved setjmp() choice operator implementation. Instead of allocating a gigantic fixed-length array of jmp_buf buffers in the data segment, we now dynamically allocate the array on the heap. The array starts at size 1 and is doubled on demand, for O(1) amortised time complexity.

This should fix the problems with very large statically allocated data observed on some platforms (cygwin, SuSE? 8.1). The new implementation should also be slightly more efficient due to inlining.

(Eelco Dolstra)

Stratego Standard Library

Posix Error Codes

The SSL has been extended with the module posix-error. This module provides strategies to report errors that have occurred in POSIX system functions. These strategies can be used to improve the error reporting of for example IO related strategies. The posix-module provides access to the errno variable and makes the strerror and perror POSIX functions available to Stratego programs. The perror strategy takes a String and produces an error message on the standard error output describing the last error encountered during a call to a system function.

The strategy chdir is for example implemented as: 

  ?pathname; prim("SSL_chdir", pathname) => 0
  <+ < conc-strings
       ; perror
       ; fail
     > ("SSL/chdir: Cannot change current working directory to ", <id>)

chdir output the following message if the pathname does not exist: 

  SSL/chdir: Cannot change current working directory to /tddmp: No
  such file or directory

(Martin Bravenboer)

String Manipulation

The new module string-misc implements miscellaneous strategies on strings. The module provides strategies for indenting, applying an s to all lines, trim trailing characters, and some more.

(Arthur van Dam)

Misc

  • set-random-seed, next-random, get-random-max: generate random numbers.

  • execv: execute a file without searching the PATH like execvp does.

  • chdir, getcwd: Change or get the working directory.

  • rename-file: in cause of external devices the file is now copied.

  • split-last: Splits a list into a tuple of its init list and last element

  • abspath, is-abspath, is-relpath, base-filename: posix compatible strategies for the manipulation of pathnames.

XTC

XTC is now using mkstemp for the creation of temporary. This means that that temporary files of XTC are from now created in the default directory for temporary files (usually /tmp).

(Martin Bravenboer)

Utilities

Pretty-Printing: Difference of Pretty-Print Tables

The pretty-print tables generated by ppgen have to be edited manually to achieve 'pretty' formatting of trees. However, when the syntax definition is updated, the edited pretty-print table should be updated as well. The new tool pptable-diff computes the differences between two pretty-print tables and prunes and patches an old table to bring it up to date with a new table. Thus, the pretty-print rules for the parts of the language that were not changed are reused.

(Merijn de Jonge)

Pack-stratego

Added --slack flag to pack-stratego. Using this will let pack-stratego continue even if a module isn't found, producing only a warning. Pack-stratego has been extended to accept absolute pathnames as input.

(Rob Vermaas)

Pack-sdf

Pack-sdf supports multiple output formats using the -of (or --output-format) flag. By default pack-sdf from now returns an SDF definition in concrete syntax (-of txt). Other supported output formats are asfix and ast. Pack-sdf from this release fails if a module is not found.

Configuration

The package name 'strategoxt' is now also reflected in the location of the XTC repository, which is in $prefix/share/strategoxt/XTC.

(Eelco Visser)

The following changes were prompted by Automake that now does check that the names of macros being defined are properly quoted. While I was at it, I have updated a couple of stylistic issues:

  • properly quote where expected
  • don't shell-quote where not needed
  • use the weak versioning conventions (#serial)

This is the resulting autoxt.m4, still valid for both Autoconf 2.1x and 2.5x, thanks!

(Valentin David)

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

NOT all the bugs and known problems for StrategoXT distributions have been solved in this release. See the stratego-bugs list for reports about (open) bugs:

For a more detailed overview of problems and missing features please visit:

Please report any problems with installation or bugs in the implementation to the stratego-bugs@cs.uu.nl mailing list. Please check the archive of the list to see if a report about the problem was already submitted.

Contributions

Developments, beta tests, and bug fixes were carried out by

  • Martin Bravenboer
  • Arthur van Dam
  • Valentin David
  • Eelco Dolstra
  • Armijn Hemel
  • Rob Vermaas
  • Eelco Visser

Special thanks to the students of the Program Transformation course.

Revision: r1.3 - 23 Jan 2004 - 09:13 - MartinBravenboer
Stratego > StrategoRelease094
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