[PATCH v2] pkl: Add exception_code to register user-defined exceptions

[Mohammad-Reza Nabipoor]

2021-01-25  Mohammad-Reza Nabipoor  <m.nabipoor@yahoo.com>

        * libpoke/pkl-rt.pk (exception_code): New function.
        * doc/poke.texi (Exceptions): Add documentation for `exception_code`.
---
 ChangeLog         |  5 +++++
 doc/poke.texi     | 14 ++++++++++++++
 libpoke/pkl-rt.pk | 13 ++++++++++++-
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index a92820ce..900a41d3 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2021-01-25  Mohammad-Reza Nabipoor  <m.nabipoor@yahoo.com>
+
+       * libpoke/pkl-rt.pk (exception_code): New function.
+       * doc/poke.texi (Exceptions): Add documentation for `exception_code`.
+
 2021-01-25  Mohammad-Reza Nabipoor  <m.nabipoor@yahoo.com>
 
        * testsuite/Makefile.am (check-DEJAGNU): Fix `make distcheck`
diff --git a/doc/poke.texi b/doc/poke.texi
index 8aeb07cb..ad36fa2f 100644
--- a/doc/poke.texi
+++ b/doc/poke.texi
@@ -10190,6 +10190,20 @@ example:
 raise Exception @{ code = 255; msg = "double upset event" @};
 @end example
 
+User-defined exceptions should be resgistered using @code{exception_code}
+function.  For example:
+
+@example
+var E_my_exception = Exception @{
+  code = exception_code,
+  msg = "double upset event",
+@};
+@end example
+
+@noindent
+where the @code{E_my_exception.code} is a unique number greater than or
+equal to @code{255}.
+
 Exception codes in the range @code{0..254} are reserved for poke.
 These are used in predefined exceptions which are standard, and have
 specific meanings:
diff --git a/libpoke/pkl-rt.pk b/libpoke/pkl-rt.pk
index 9947d4d3..658ecd37 100644
--- a/libpoke/pkl-rt.pk
+++ b/libpoke/pkl-rt.pk
@@ -77,7 +77,8 @@ type Exception =
 /* Standard exception codes.
    These codes should be in sync with PVM_E_* macros in pvm.h.
    Note that user-defined exceptions must have codes starting with
-   255.
+   255 (and should be registered using exception_code function defined
+   below).
    Note also that EC_generic _must_ be zero.  */
 
 var EC_generic       = 0;
@@ -135,6 +136,16 @@ var E_exit
 var E_assert
   = Exception {code = EC_assert, msg = "assertion failure", exit_status = 1};
 
+/* Registration of user-defined exceptions */
+
+type _ExceptionCodeGenerator = () int<32>;
+var exception_code = lambda _ExceptionCodeGenerator:
+  {
+    var n = 255; /* First available code for user-defined exceptions */
+
+    return lambda int<32>: { return n++; };
+  }();
+
 /* Default exception handler.
 
    Note that the code in this function should NOT raise any exception,
-- 
2.30.0