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.
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 Stratego/XT support Microsoft Windows?
A: Yes, Stratego/XT works on Microsoft Windows + Cygwin. We provide binary distributions.
Q: Does Stratego/XT support Mac OS X?
A: Yes, Stratego/XT works on Mac OS X. We provide binary distributions.
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.
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
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.
Q: I get unexpected behaviour with two different dynamic rules with the same label.
A: If you are not using Stratego/XT 0.14 or later please upgrade. For more information see dynamic rule semantics.
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 is part of the Stratego Library.