About this FAQ
Q: Is there a list of Frequently Asked Questions about Stratego?
A: Until now there wasn't. This page is the place to ask questions and look for answers. If you have a question, add it here.
Installation
Q: I get errors when compiling Stratego programs or when running compiled Stratego programs.
A: If you've carefully followed the
installation instructions and you are still having problems, please file a
bug report. Make sure to specify your configuration (OS, gcc version, Stratego version), include the error message and if posisble try to reduce
to problem to a small piece of code.
Q: Does
StrategoXT support Microsoft Windows?
A: StrategoXT should more or less work on Microsoft Windows + Cygwin. More or less is however not precise enough, so we are currently investigating whether there are any real problems with
Microsoft Windows support. A firm answer is scheduled for
StrategoXT 0.9.3. In the near future we will test
Microsoft Windows support in the
daily build system.
Stratego interpreter
Q: How do I proceed to write Stratego code that's both interpretable and
compilable? Is that a goal for the interpreter that this is possible ?
A: Yes, the compiler and the interpreter work on the same language. You
can consider the list of commands in a script as the main strategy of
a specification. There should be no difference in semantics between the
compiler and the interpreter. Except for the fact that there is a definition
before use regime in the script itself (not in modules imported in the script).
That is, that is defined in the script can only be used (in a command) after
it has been declared.
Debugging
Q: How do I get more debugging info ? The tools are awfully quiet unless I chock
my code full of
debug invocations. Can I somehow set up an 'exception
handler' that shows the traversed stack and line number (or something similar)
when a rewriting fails miserably?
A: See
debugging techniques
Stratego language
Q: What is the difference between a strategy and a rule?
A: See
rules versus strategies
Q: In what ways can variables be bound?
A: A variable is only bound during matching. That is, while applying a pattern match
?t to the subject term. All constructs that bind variables, ultimately use this pattern matching construct to bind variables.
Dynamic rules
Q: I get unexpected behaviour with two different dynamic rules with the same label.
A: If you are not using
StrategoXT 0.9 or later please upgrade. For more information see
dynamic rule semantics.
Stratego standard libary
Q: collect removes duplicates, is there
collect-with-duplicates?
A: Yes, there is. The collect strategy is an alias of
collect-om.
collect-om has a variant that takes a strategy argument that is used to combine intermediate results. If you pass
conc instead of
union, then duplicates will not be removed.
Q: Is it possible to redirect the stderr of process to a file in Stratego?
A: Yes, this works exactly the same a redirection in C. Example:
module example
imports posix-file char-io
strategies
main =
<open> "error.txt" => fd
; <dup2> (fd, <STDERR_FILENO>)
; <debug> "bla bla bla 1"
; <fputs> ("bla bla bla 2", <stderr-stream>)
; <close> fd
See 'man dup2' for more information.
If you want to execute a new process, the following strategy is useful:
/**
* Execute program in a new process with list of string args,
* with the specified exec strategy.
*
* Optionally you can define file descriptors to use for stdin, stdout,
* stderr.
*
* @param opt-fdin Option(FileDescr)
* @param opt-fdout Option(FileDescr)
* @param opt-fderr Option(FileDescr)
*
* @type (String, List(String)) -> ()
*/
call(|opt-fdin, opt-fdout, opt-fderr) =
?(prog, args)
; fork-and-wait(
<option(<dup2> (<id>, <STDIN_FILENO> ))> opt-fdin
; <option(<dup2> (<id>, <STDOUT_FILENO>))> opt-fdout
; <option(<dup2> (<id>, <STDERR_FILENO>))> opt-fderr
; <execvp> (prog, args)
; <exit> 1
)
; !()
This strategy might become part of the SSL in the future.