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system.onRaise improvements
This commit is contained in:
Araq
236
doc/manual.txt
236
doc/manual.txt
@@ -1969,116 +1969,6 @@ a special syntactic extension, the ``when`` construct is also available
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within ``object`` definitions.
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Try statement
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~~~~~~~~~~~~~
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Syntax::
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qualifiedIdent ::= symbol ['.' symbol]
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exceptList ::= [qualifiedIdent (comma qualifiedIdent)* [comma]]
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tryStmt ::= 'try' ':' stmt
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('except' exceptList ':' stmt)*
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['finally' ':' stmt]
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Example:
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.. code-block:: nimrod
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# read the first two lines of a text file that should contain numbers
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# and tries to add them
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var
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f: TFile
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if open(f, "numbers.txt"):
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try:
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var a = readLine(f)
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var b = readLine(f)
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echo("sum: " & $(parseInt(a) + parseInt(b)))
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except EOverflow:
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echo("overflow!")
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except EInvalidValue:
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echo("could not convert string to integer")
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except EIO:
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echo("IO error!")
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except:
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echo("Unknown exception!")
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finally:
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close(f)
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The statements after the `try`:idx: are executed in sequential order unless
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an exception ``e`` is raised. If the exception type of ``e`` matches any
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of the list ``exceptlist`` the corresponding statements are executed.
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The statements following the ``except`` clauses are called
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`exception handlers`:idx:.
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The empty `except`:idx: clause is executed if there is an exception that is
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in no list. It is similar to an ``else`` clause in ``if`` statements.
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If there is a `finally`:idx: clause, it is always executed after the
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exception handlers.
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The exception is *consumed* in an exception handler. However, an
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exception handler may raise another exception. If the exception is not
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handled, it is propagated through the call stack. This means that often
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the rest of the procedure - that is not within a ``finally`` clause -
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is not executed (if an exception occurs).
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Except and finally statements
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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`except`:idx: and `finally`:idx: can also be used as a stand-alone statements.
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Any statements following them in the current block will be considered to be
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in an implicit try block:
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.. code-block:: nimrod
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var f = open("numbers.txt")
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finally: close(f)
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...
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Raise statement
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~~~~~~~~~~~~~~~
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Syntax::
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raiseStmt ::= 'raise' [expr]
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Example:
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.. code-block:: nimrod
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raise newEOS("operating system failed")
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Apart from built-in operations like array indexing, memory allocation, etc.
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the ``raise`` statement is the only way to raise an exception.
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.. XXX document this better!
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If no exception name is given, the current exception is `re-raised`:idx:. The
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`ENoExceptionToReraise`:idx: exception is raised if there is no exception to
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re-raise. It follows that the ``raise`` statement *always* raises an
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exception (unless a raise hook has been provided).
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OnRaise builtin
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~~~~~~~~~~~~~~~
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``system.onRaise`` can be used to override the behaviour of ``raise`` for a
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single ``try`` statement. `onRaise`:idx: has to be called within the ``try``
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statement that should be affected.
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This allows for a Lisp-like `condition system`:idx:\:
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.. code-block:: nimrod
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var myFile = open("broken.txt", fmWrite)
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try:
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onRaise(proc (e: ref E_Base): bool =
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stdout.writeln "ok, writing to stdout instead")
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myFile.writeln "writing to broken file"
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finally:
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myFile.close()
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Return statement
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~~~~~~~~~~~~~~~~
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@@ -2781,6 +2671,132 @@ can be recursive or even mutually recursive. Mutually recursive types are only
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possible within a single ``type`` section.
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Exception handling
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------------------
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Try statement
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~~~~~~~~~~~~~
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Syntax::
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qualifiedIdent ::= symbol ['.' symbol]
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exceptList ::= [qualifiedIdent (comma qualifiedIdent)* [comma]]
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tryStmt ::= 'try' ':' stmt
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('except' exceptList ':' stmt)*
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['finally' ':' stmt]
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Example:
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.. code-block:: nimrod
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# read the first two lines of a text file that should contain numbers
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# and tries to add them
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var
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f: TFile
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if open(f, "numbers.txt"):
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try:
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var a = readLine(f)
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var b = readLine(f)
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echo("sum: " & $(parseInt(a) + parseInt(b)))
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except EOverflow:
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echo("overflow!")
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except EInvalidValue:
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echo("could not convert string to integer")
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except EIO:
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echo("IO error!")
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except:
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echo("Unknown exception!")
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finally:
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close(f)
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The statements after the `try`:idx: are executed in sequential order unless
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an exception ``e`` is raised. If the exception type of ``e`` matches any
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of the list ``exceptlist`` the corresponding statements are executed.
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The statements following the ``except`` clauses are called
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`exception handlers`:idx:.
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The empty `except`:idx: clause is executed if there is an exception that is
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in no list. It is similar to an ``else`` clause in ``if`` statements.
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If there is a `finally`:idx: clause, it is always executed after the
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exception handlers.
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The exception is *consumed* in an exception handler. However, an
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exception handler may raise another exception. If the exception is not
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handled, it is propagated through the call stack. This means that often
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the rest of the procedure - that is not within a ``finally`` clause -
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is not executed (if an exception occurs).
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Except and finally statements
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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`except`:idx: and `finally`:idx: can also be used as a stand-alone statements.
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Any statements following them in the current block will be considered to be
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in an implicit try block:
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.. code-block:: nimrod
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var f = open("numbers.txt")
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finally: close(f)
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...
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Raise statement
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~~~~~~~~~~~~~~~
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Syntax::
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raiseStmt ::= 'raise' [expr]
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Example:
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.. code-block:: nimrod
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raise newEOS("operating system failed")
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Apart from built-in operations like array indexing, memory allocation, etc.
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the ``raise`` statement is the only way to raise an exception.
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.. XXX document this better!
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If no exception name is given, the current exception is `re-raised`:idx:. The
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`ENoExceptionToReraise`:idx: exception is raised if there is no exception to
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re-raise. It follows that the ``raise`` statement *always* raises an
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exception (unless a raise hook has been provided).
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OnRaise builtin
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~~~~~~~~~~~~~~~
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``system.onRaise`` can be used to override the behaviour of ``raise`` for a
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single ``try`` statement. `onRaise`:idx: has to be called within the ``try``
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statement that should be affected.
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This allows for a Lisp-like `condition system`:idx:\:
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.. code-block:: nimrod
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var myFile = open("broken.txt", fmWrite)
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try:
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onRaise(proc (e: ref E_Base): bool =
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stdout.writeln "ok, writing to stdout instead")
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myFile.writeln "writing to broken file"
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finally:
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myFile.close()
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Exception tracking
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~~~~~~~~~~~~~~~~~~
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Nimrod supports `exception tracking`:idx:. XXX
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- Raises pragma
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- Inference rules
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* Forwarding rule
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* Multi-method rule
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* proc type rule
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- Effects pragma
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Generics
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--------
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@@ -1941,6 +1941,7 @@ when not defined(EcmaScript) and not defined(NimrodVM):
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prev: PSafePoint # points to next safe point ON THE STACK
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status: int
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context: C_JmpBuf
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hasRaiseAction: bool
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raiseAction: proc (e: ref E_Base): bool {.closure.}
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when defined(initAllocator):
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@@ -2047,7 +2048,9 @@ when not defined(EcmaScript) and not defined(NimrodVM):
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## raise an exception but instead calls ``action``.
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## If ``action`` returns false, the exception has been handled and
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## does not propagate further through the call stack.
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if not isNil(excHandler): excHandler.raiseAction = action
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if not isNil(excHandler):
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excHandler.hasRaiseAction = true
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excHandler.raiseAction = action
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{.push stack_trace: off, profiler:off.}
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when defined(endb):
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@@ -51,8 +51,8 @@ proc popFrame {.compilerRtl, inl.} =
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proc setFrame(s: PFrame) {.compilerRtl, inl.} =
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framePtr = s
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proc pushSafePoint(s: PSafePoint) {.compilerRtl, inl.} =
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s.raiseAction = nil
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proc pushSafePoint(s: PSafePoint) {.compilerRtl, inl.} =
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s.hasRaiseAction = false
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s.prev = excHandler
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excHandler = s
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@@ -199,7 +199,7 @@ proc raiseExceptionAux(e: ref E_Base) =
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if globalRaiseHook != nil:
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if not globalRaiseHook(e): return
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if excHandler != nil:
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if isNil(excHandler.raiseAction) or excHandler.raiseAction(e):
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if not excHandler.hasRaiseAction or excHandler.raiseAction(e):
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pushCurrentException(e)
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c_longjmp(excHandler.context, 1)
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elif e[] of EOutOfMemory:
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