6.18 Exceptions

8.12

6.18 Exceptions🔗ℹ

expression

try:

...

maybe_initially	=	~initially: body; ...
	\|	~initially expr
	\|	ϵ

maybe_catch

~catch bind: body; ...

~catch

| bind: body; ...

| ...

maybe_finally	=	~finally: body; ...
	\|	~finally expr
	\|	ϵ

Returns the value of the body sequence, but runs the body or expression of an ~initially clause when entry the try body (whether normally or by a continuation jump) and the body or expression of a ~finally clause when leaving the try body (whether normally or by a continuation jump, including exception throws).

If an excepotion is thrown during the the body sequence, the control escapes to the context of the try body sequence (i.e., “inside” the ~initially and ~finally guards) and the ~catch cases are tried in order. When a ~catch binding matches, then the result of the try form is the body of the ~catch clause. If no ~catch clause matches, the exception is re-thrown. Breaks are disabled while attempting to match a ~catch clause or evaluating its body.

The last body form of try are not in tail position is any of ~initially, ~catch, or ~finally is present. If none are present, the try form is the same as begin.

> try:
    ~initially: println("in")
    "ok"
    ~finally: println("out")
in
out
"ok"

> try:
    ~initially: println("in")
    1/0
    ~finally: println("out")
in
out
/: division by zero

> try:
    1/0
    ~catch exn :: Exn.Fail.Contract.DivideByZero:
      "handled"
"handled"

> try:
    ~initially: println("in")
    1/0
    ~catch _:
      println("ignoring all exceptions!")
      0
    ~finally: println("out")
in
ignoring all exceptions!
out
0

> def k:
    Continuation.prompt:
      try:
        ~initially: println("in")
        Continuation.capture k: k
        ~finally: println("out")
in
out
> k("again")
in
out
"again"

expression

throw expr

Throws the value of expr as an exception. Any value can be thrown, but typically thrown values are instances of a subclass of Exn.

function

fun error(message :: ReadableString)

:: None

function

fun error(

who :: maybe(ReadableString || Symbol || Identifier || Operator),

message :: ReadableString

) :: None

Throws the Exn.Fail exception with message as the message and Continuation.Marks.current() as the continuation marks. If who is not #false, it is added to the beginning of the message, and a : separator is added in between.

class

class Exn(message :: ReadableString, marks :: Continuation.Marks)

class

class Exn.Fail():

extends Exn

class

class Exn.Fail.Contract():

extends Exn.Fail

class

class Exn.Fail.Contract.Arity():

extends Exn.Fail.Contract

class

class Exn.Fail.Contract.DivideByZero():

extends Exn.Fail.Contract

class

class Exn.Fail.Contract.NonFixnumResult():

extends Exn.Fail.Contract

class

class Exn.Fail.Contract.Continuation():

extends Exn.Fail.Contract

class

class Exn.Fail.Contract.Variable(id :: Symbol):

extends Exn.Fail.Contract

class

class Exn.Fail.Syntax(exprs :: PairList.of(Syntax)):

extends Exn.Fail

class

class Exn.Fail.Syntax.Unbound():

extends Exn.Fail.Syntax

class

class Exn.Fail.Syntax.MissingModule(path):

extends Exn.Fail.Syntax

class

class Exn.Fail.Read(srclocs :: PairList.of(Srcloc)):

extends Exn.Fail

class

class Exn.Fail.Read.EOF():

extends Exn.Fail.Read

class

class Exn.Fail.Read.NonChar():

extends Exn.Fail.Read

class

class Exn.Fail.Filesystem():

extends Exn.Fail

class

class Exn.Fail.Filesystem.Exists():

extends Exn.Fail.Filesystem

class

class Exn.Fail.Filesystem.Version():

extends Exn.Fail.Filesystem

class

class Exn.Fail.Filesystem.Errno(errno :: Pair.of(Symbol, Int)):

extends Exn.Fail.Filesystem

class

class Exn.Fail.Filesystem.MissingModule(path):

extends Exn.Fail.Filesystem

class

class Exn.Fail.Network():

extends Exn.Fail

class

class Exn.Fail.Network():

extends Exn.Fail.Network

class

class Exn.Fail.Network.Errno(errno :: Pair.of(Symbol, Int)):

extends Exn.Fail.Network

class

class Exn.Fail.OutOfMemory():

extends Exn.Fail

class

class Exn.Fail.Unsupported():

extends Exn.Fail

class

class Exn.Fail.User():

extends Exn.Fail

class

class Exn.Break(continuation :: Continuation):

extends Exn

class

class Exn.Break.HangUp():

extends Exn.Break

class

class Exn.Break.Terminate():

extends Exn.Break

Primitive exceptions.

1	Rhombus Essentials
2	Collections and Iteration
3	Syntax Objects and Macros
4	Classes and Interfaces
5	Static Information and Binding
6	Core Reference
7	Meta and Macros Reference
8	Rhombus Static by Default
9	Libraries
10	Naming Conventions

6.1	General Forms
6.2	Definitions
6.3	Namespaces
6.4	Import
6.5	Export
6.6	Functions
6.7	Operators
6.8	Classes and Interfaces
6.9	Veneers
6.10	Mutable Variables and Assignment
6.11	Repetitions
6.12	Block
6.13	Conditionals
6.14	Matching
6.15	Iteration
6.16	Recursion
6.17	Context Parameters
6.18	Exceptions
6.19	Continuations
6.20	Implicit Forms
6.21	Static and Dynamic Lookup
6.22	Modules and Submodules
6.23	Booleans
6.24	Numbers
6.25	Characters
6.26	Strings
6.27	Keywords
6.28	Symbols
6.29	Byte Strings
6.30	Lists
6.31	Pairs and Pair Lists
6.32	Mutable Lists
6.33	Arrays
6.34	Maps
6.35	Sets
6.36	Boxes
6.37	Indexables
6.38	Listables
6.39	Sequences
6.40	Appendables
6.41	Comparables
6.42	Paths
6.43	Source Locations
6.44	Void
6.45	Equality
6.46	Dot
6.47	Multiple Values
6.48	Annotations
6.49	Enumerations
6.50	Input and Output
6.51	Eval
6.52	Syntax Objects
6.53	Syntax Classes
6.54	Simple Expression Macros
6.55	Unit Testing