Previous: Condition Types, Up: Error System [Contents][Index]
The MIT/GNU Scheme error system provides a rich set of predefined condition
types. These are organized into a forest through taxonomic links
providing the relationships for “specializes” and “generalizes”.
The chart appearing below shows these relationships by indenting all the
specializations of a given type relative to the type. Note that the
variables that are bound to these condition types are prefixed by
‘condition-type:’; for example, the type appearing in the following
table as ‘simple-error’ is stored in the variable
condition-type:simple-error. Users are encouraged to add new
condition types by creating specializations of existing ones.
Following the chart are detailed descriptions of the predefined condition types. Some of these types are marked as abstract types. Abstract types are not intended to be used directly as the type of a condition; they are to be used as generalizations of other types, and for binding condition handlers. Types that are not marked as abstract are concrete; they are intended to be explicitly used as a condition’s type.
serious-condition
error
simple-error
illegal-datum
wrong-type-datum
wrong-type-argument
wrong-number-of-arguments
datum-out-of-range
bad-range-argument
inapplicable-object
file-error
file-operation-error
derived-file-error
port-error
derived-port-error
variable-error
unbound-variable
unassigned-variable
arithmetic-error
divide-by-zero
floating-point-overflow
floating-point-underflow
control-error
no-such-restart
not-loading
primitive-procedure-error
system-call-error
warning
simple-warning
simple-condition
breakpoint
This is an abstract type. All serious conditions that require some form of intervention should inherit from this type. In particular, all errors inherit from this type.
This is an abstract type. All errors should inherit from this type.
This is the condition generated by the error procedure when its
first argument is not a condition or condition type. The fields
message and irritants are taken directly from the arguments
to error; message contains an object (usually a string) and
irritants contains a list of objects. The reporter for this type
uses format-error-message to generate its output from
message and irritants.
This is an abstract type. This type indicates the class of errors in which a program discovers an object that lacks specific required properties. Most commonly, the object is of the wrong type or is outside a specific range. The datum field contains the offending object.
This type indicates the class of errors in which a program discovers an object that is of the wrong type. The type field contains a string describing the type that was expected, and the datum field contains the object that is of the wrong type.
(error:wrong-type-datum 3.4 "integer") error→ ;The object 3.4 is not an integer. ;To continue, call RESTART with an option number: ; (RESTART 1) => Return to read-eval-print level 1.
This procedure signals a condition of type
condition-type:wrong-type-datum. The datum and type
fields of the condition are filled in from the corresponding arguments
to the procedure.
This type indicates that a procedure was passed an argument of the wrong
type. The operator field contains the procedure (or a symbol
naming the procedure), the operand field indicates the argument
position that was involved (this field contains either a symbol, a
non-negative integer, or #f), the type field contains a
string describing the type that was expected, and the datum field
contains the offending argument.
(+ 'a 3) error→ ;The object a, passed as the first argument to integer-add, ; is not the correct type. ;To continue, call RESTART with an option number: ; (RESTART 2) => Specify an argument to use in its place. ; (RESTART 1) => Return to read-eval-print level 1.
(list-copy 3) ;The object 3, passed as an argument to list-copy, is not a list. ;To continue, call RESTART with an option number: ; (RESTART 1) => Return to read-eval-print level 1.
This procedure signals a condition of type
condition-type:wrong-type-argument. The datum, type
and operator fields of the condition are filled in from the
corresponding arguments to the procedure; the operand field of the
condition is set to #f.
This type indicates that a procedure was called with the wrong number of arguments. The datum field contains the procedure being called, the type field contains the number of arguments that the procedure accepts, and the operands field contains a list of the arguments that were passed to the procedure.
(car 3 4) error→ ;The procedure car has been called with 2 arguments; ; it requires exactly 1 argument. ;To continue, call RESTART with an option number: ; (RESTART 1) => Return to read-eval-print level 1.
This procedure signals a condition of type
condition-type:wrong-number-of-arguments. The datum,
type and operands fields of the condition are filled in from
the corresponding arguments to the procedure.
This type indicates the class of errors in which a program discovers an object that is of the correct type but is otherwise out of range. Most often, this type indicates that an index to some data structure is outside of the range of indices for that structure. The datum field contains the offending object.
(error:datum-out-of-range 3) error→ ;The object 3 is not in the correct range. ;To continue, call RESTART with an option number: ; (RESTART 1) => Return to read-eval-print level 1.
This procedure signals a condition of type
condition-type:datum-out-of-range. The datum field of the
condition is filled in from the corresponding argument to the procedure.
This type indicates that a procedure was passed an argument that is of
the correct type but is otherwise out of range. Most often, this type
indicates that an index to some data structure is outside of the range
of indices for that structure. The operator field contains the
procedure (or a symbol naming the procedure), the operand field
indicates the argument position that was involved (this field contains
either a symbol, a non-negative integer, or #f), and the
datum field is the offending argument.
(string-ref "abc" 3) error→ ;The object 3, passed as the second argument to string-ref, ; is not in the correct range. ;To continue, call RESTART with an option number: ; (RESTART 2) => Specify an argument to use in its place. ; (RESTART 1) => Return to read-eval-print level 1.
This procedure signals a condition of type
condition-type:bad-range-argument. The datum and
operator fields of the condition are filled in from the
corresponding arguments to the procedure; the operand field of the
condition is set to #f.
This type indicates an error in which a program attempted to apply an object that is not a procedure. The object being applied is saved in the datum field, and the arguments being passed to the object are saved as a list in the operands field.
(3 4) error→ ;The object 3 is not applicable. ;To continue, call RESTART with an option number: ; (RESTART 2) => Specify a procedure to use in its place. ; (RESTART 1) => Return to read-eval-print level 1.
This is an abstract type. It indicates that an error associated with a file has occurred. For example, attempting to delete a nonexistent file will signal an error. The filename field contains a filename or pathname associated with the operation that failed.
This is the most common condition type for file system errors. The filename field contains the filename or pathname that was being operated on. The verb field contains a string which is the verb or verb phrase describing the operation being performed, and the noun field contains a string which is a noun or noun phrase describing the object being operated on. The reason field contains a string describing the error that occurred. The operator field contains the procedure performing the operation (or a symbol naming that procedure), and the operands field contains a list of the arguments that were passed to that procedure. For example, an attempt to delete a nonexistent file would have the following field values:
filename "/zu/cph/tmp/no-such-file"
verb "delete"
noun "file"
reason "no such file or directory"
operator file-remove
operands ("/zu/cph/tmp/no-such-file")
and would generate a message like this:
(delete-file "/zu/cph/tmp/no-such-file") error→ ;Unable to delete file "/zu/cph/tmp/no-such-file" because: ; No such file or directory. ;To continue, call RESTART with an option number: ; (RESTART 3) => Try to delete the same file again. ; (RESTART 2) => Try to delete a different file. ; (RESTART 1) => Return to read-eval-print level 1.
This procedure signals a condition of type
condition-type:file-operation-error. The fields of the
condition are filled in from the corresponding arguments to the
procedure, except that the filename is taken as the indexth
element of operands.
This is another kind of file error, which is generated by obscure
file-system errors that do not fit into the standard categories. The
filename field contains the filename or pathname that was being
operated on, and the condition field contains a condition
describing the error in more detail. Usually the condition field
contains a condition of type condition-type:system-call-error.
This procedure signals a condition of type
condition-type:derived-file-error. The filename and
condition fields of the condition are filled in from the
corresponding arguments to the procedure.
This is an abstract type. It indicates that an error associated with a I/O port has occurred. For example, writing output to a file port can signal an error if the disk containing the file is full; that error would be signalled as a port error. The port field contains the associated port.
This is a concrete type that is signalled when port errors occur. The
port field contains the port associated with the error, and the
condition field contains a condition object that describes the
error in more detail. Usually the condition field contains a
condition of type condition-type:system-call-error.
This procedure signals a condition of type
condition-type:derived-port-error. The port and
condition fields of the condition are filled in from the
corresponding arguments to the procedure.
This is an abstract type. It indicates that an error associated with a variable has occurred. The location field contains the name of the variable, and the environment field contains the environment in which the variable was referenced.
This type is generated when a program attempts to access or modify a variable that is not bound. The location field contains the name of the variable, and the environment field contains the environment in which the reference occurred.
foo error→ ;Unbound variable: foo ;To continue, call RESTART with an option number: ; (RESTART 3) => Specify a value to use instead of foo. ; (RESTART 2) => Define foo to a given value. ; (RESTART 1) => Return to read-eval-print level 1.
This type is generated when a program attempts to access a variable that is not assigned. The location field contains the name of the variable, and the environment field contains the environment in which the reference occurred.
foo error→ ;Unassigned variable: foo ;To continue, call RESTART with an option number: ; (RESTART 3) => Specify a value to use instead of foo. ; (RESTART 2) => Set foo to a given value. ; (RESTART 1) => Return to read-eval-print level 1.
This is an abstract type. It indicates that a numerical operation was unable to complete because of an arithmetic error. (For example, division by zero.) The operator field contains the procedure that implements the operation (or a symbol naming the procedure), and the operands field contains a list of the arguments that were passed to the procedure.
This type is generated when a program attempts to divide by zero. The operator field contains the procedure that implements the failing operation (or a symbol naming the procedure), and the operands field contains a list of the arguments that were passed to the procedure.
(/ 1 0) ;Division by zero signalled by /. ;To continue, call RESTART with an option number: ; (RESTART 1) => Return to read-eval-print level 1.
This procedure signals a condition of type
condition-type:divide-by-zero. The operator and
operands fields of the condition are filled in from the
corresponding arguments to the procedure.
This type is generated when a program performs an arithmetic operation that results in a floating-point overflow. The operator field contains the procedure that implements the operation (or a symbol naming the procedure), and the operands field contains a list of the arguments that were passed to the procedure.
This type is generated when a program performs an arithmetic operation that results in a floating-point underflow. The operator field contains the procedure that implements the operation (or a symbol naming the procedure), and the operands field contains a list of the arguments that were passed to the procedure.
This is an abstract type. It indicates that an error was generated by a primitive procedure call. Primitive procedures are distinguished from ordinary procedures in that they are not written in Scheme but instead in the underlying language of the Scheme implementation. The operator field contains the procedure that implements the operation (or a symbol naming the procedure), and the operands field contains a list of the arguments that were passed to the procedure.
This is the most common condition type generated by primitive
procedures. A condition of this type indicates that the primitive made
a system call to the operating system, and that the system call
signalled an error. The system-call error is reflected back to Scheme
as a condition of this type, except that many common system-call errors
are automatically translated by the Scheme implementation into more
useful forms; for example, a system-call error that occurs while trying
to delete a file will be translated into a condition of type
condition-type:file-operation-error. The operator field
contains the procedure that implements the operation (or a symbol naming
the procedure), and the operands field contains a list of the
arguments that were passed to the procedure. The system-call and
error-type fields contain symbols that describe the specific
system call that was being made and the error that occurred,
respectively; these symbols are completely operating-system dependent.
This is an abstract type. It describes a class of errors relating to program control flow.
This type indicates that a named restart was not active when it was
expected to be. Conditions of this type are signalled by several
procedures that look for particular named restarts, for example
muffle-warning. The name field contains the name that was
being searched for.
(muffle-warning) error→ ;The restart named muffle-warning is not bound. ;To continue, call RESTART with an option number: ; (RESTART 1) => Return to read-eval-print level 1.
This procedure signals a condition of type
condition-type:no-such-restart. The name field of the
condition is filled in from the corresponding argument to the procedure.
A condition of this type is generated when the procedure
current-load-pathname is called from somewhere other than inside
a file being loaded.
(current-load-pathname) error→ ;No file being loaded. ;To continue, call RESTART with an option number: ; (RESTART 1) => Return to read-eval-print level 1.
This is an abstract type. All warnings should inherit from this type. Warnings are a class of conditions that are usually handled by informing the user of the condition and proceeding the computation normally.
This is the condition generated by the warn procedure. The
fields message and irritants are taken directly from the
arguments to warn; message contains an object (usually a
string) and irritants contains a list of objects. The reporter
for this type uses format-error-message to generate its output
from message and irritants.
This is an unspecialized condition that does not fall into any of the
standard condition classes. The message field contains an object
(usually a string) and irritants contains a list of objects. The
reporter for this type uses format-error-message to generate its
output from message and irritants.
A condition of this type is generated by the breakpoint mechanism. The contents of its fields are beyond the scope of this document.
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