# The Common Lisp Condition System
## 0. Preface
### 0.1 Abstract
### 0.2 What is a condition system? Introduction by Kent M. Pitman
### 0.3 Daydreaming
### 0.4 Preface
### 0.5 Hall of Fame
## 1 Basic concepts
### 1.1 Dynamic variables
#### 1.1.1 Dynamic variables in C
##### 1.1.1.1 Implementing dynamic variables in C
#### 1.1.2 Dynamic variables in Common Lisp
#### 1.1.3 Alternatives in other languages
##### 1.1.3.1 Scheme
##### 1.1.3.2 Design patterns
### 1.2 Non-local transfers of control
#### 1.2.1 `TAGBODY` and `GO`
#### 1.2.2 `BLOCK` and `RETURN-FROM`/`RETURN`
#### 1.2.3 `CATCH` and `THROW`
### 1.3 Lexical closures
## 2 Introducing the condition system
### 2.1 A simple system of hooks
#### 2.1.1 Hook #1: launching Counter Strike
##### 2.1.1.1 Equivalent examples
#### 2.1.2 Hook #2: only call Counter Strike players
#### 2.1.3 Hook #3: only call parents... maybe
#### 2.1.4 Hook #4: holiday wishes
#### 2.1.5 Accumulating hooks
#### 2.1.6 Hook #5: calling Tom's girlfriend again
#### 2.1.7 Multiple types of hooks
#### 2.1.8 Summary: the hook subsystem
### 2.2 A simple system of condition handlers
#### 2.2.1 Exception handling
##### 2.2.1.1 First iteration: no handling
##### 2.2.1.2 Second iteration: signaling a condition
##### 2.2.1.3 Third iteration: entering the debugger
#### 2.2.2 Protection against transfers of control
#### 2.2.3 Clustering
#### 2.2.4 Summary: the handler subsystem
### 2.3 A simple system of choices
#### 2.3.1 Kate and Mark
#### 2.3.2 Choice #1: escape
##### 2.3.2.1 The CHOICE structure
##### 2.3.2.2 Escaping through the front door
##### 2.3.2.3 Escaping through the back door
##### 2.3.2.4 Computing and invoking choices
##### 2.3.2.5 The results
##### 2.3.2.6 Same-named choices
#### 2.3.3 Choice #2: excuses
#### 2.3.4 Summary: the choice subsystem
### 2.4 A simple system of restarts
#### 2.4.1 Interactive restarts
### 2.5 A simple system of actually-restarting restarts
#### 2.5.1 Restarts that perform a non-local exit
#### 2.5.2 From RESTART-BIND to RESTART-CASE
#### 2.5.3 Simple restarts
#### 2.5.4 Standard restarts and restart-invoking functions
#### 2.5.5 Defining custom restart-invoking functions
### 2.6 Reporting conditions and restarts
#### 2.6.1 Printing versus reporting
#### 2.6.2 Custom condition reports
#### 2.6.3 Custom restart reports
### 2.7 Warnings
#### 2.7.1 Different ways of warning
#### 2.7.2 Muffling warnings
### 2.8 Assertions
#### 2.8.1 Simple assertions via ASSERT
#### 2.8.2 Typechecking via CHECK-TYPE
#### 2.8.3 Case assertions
#### 2.8.3 Correctable case assertions
#### 2.8.4 Arguments for continuable errors
### 2.9 A simple debugger
#### 2.9.1 Reporting the condition in the debugger
#### 2.9.2 Reporting the condition type in the debugger
#### 2.9.3 Reporting the restarts in the debugger
#### 2.9.4 Choosing the restarts in the debugger
#### 2.9.5 Installing a custom debugger
#### 2.9.6 Recursive debugger
#### 2.9.7 Adding a REPL to the debugger
#### 2.9.8 Backtraces
#### 2.9.9 Associating conditions with restarts
## 3 Implementing the Common Lisp condition system
### 3.1 Package definition
### 3.2 Conditions
#### 3.2.1 Base class for conditions
#### 3.2.2 Defining new condition types
### 3.3 Coercing data to conditions
### 3.4 Restart basics
#### 3.4.1 Restart class
#### 3.4.2 Restart visibility and computing restarts
#### 3.4.3 Invoking restarts
### 3.5 Binding restarts
### 3.6 Restart cases
#### 3.6.1 First iteration: basics
#### 3.6.2 Second iteration: forms instead of a function
#### 3.6.3 Third iteration: managing the keyword differences
#### 3.6.4 Fourth iteration: associating conditions with restarts
#### 3.6.5 Implementing simple restarts
### 3.7 System-defined restarts
### 3.8 Assertions
#### 3.8.1 Case failures
#### 3.8.2 Case utilities
#### 3.8.3 Non-correctable case assertions
#### 3.8.4 Correctable case assertions
#### 3.8.5 General assertions
### 3.9 Signaling
### 3.10 Handlers
#### 3.10.1 Binding handlers
#### 3.10.2 Handler cases
#### 3.10.3 Testing assertions
### 3.11 A featureful debugger
#### 3.11.1 Debugger commands
#### 3.11.2 Evaluating Lisp forms
#### 3.11.3 Reporting and returning conditions
#### 3.11.4 Listing and invoking restarts
#### 3.11.5 Debugger help and REPL
##### 3.11.5.1 REPL variables
##### 3.11.5.2 Debugger read-eval-print step
#### 3.11.6 Debugger interface
### 3.12 Finishing touches
#### 3.12.1 Integration
#### 3.12.2 Additional work
## 4 Wrapping up
### 4.1 The purpose of the condition system
### 4.2 Binding versus casing
### 4.3 Separation of concerns
### 4.4 Algebraic effects
### 4.5 Downsides of the condition system
#### 4.5.1 Separation from CLOS
##### 4.5.1.1 Making conditions of complex condition types
#### 4.5.2 Dynamic extent of restart objects
#### 4.5.3 Speed
#### 4.5.4 Optimization settings
#### 4.5.5 Introspection
#### 4.5.6 Concrete condition types
#### 4.5.7 Warning conditions and #'WARN
#### 4.5.8 Implementing custom SIGNAL-like operators
#### 4.5.9 Lack of functional interfaces to handlers and restarts
#### 4.5.10 Smaller issues
#### 4.5.11 Summary: downsides of the Common Lisp condition system
## 4.6 Condition system in practice
### 4.6.1 Unit test library: collecting results
### 4.6.2 Web framework: sending results over the network
### 4.6.3 GUI applications: interactive querying
### 4.6.4 Generating data: Python-like generators
## 5 Appendices
### 5.1 Appendix A: Implementation of dynamic variables in C
### 5.2 Appendix B: Additional utilities for working with Common Lisp conditions
#### 5.2.1 CALL-WITH-HANDLER and CALL-WITH-RESTART
#### 5.2.2 HANDLER-BIND\* and HANDLER-CASE\*
#### 5.2.3 HANDLER-BIND-CASE
### 5.3 Appendix C: Lisp macros 101
#### 5.3.1 Basics of macro writing
#### 5.3.2 Backquote
#### 5.3.3 Symbol capture
#### 5.3.4 Order of evaluation
#### 5.3.5 Multiple evaluation
#### 5.3.6 When not to write macros
#### 5.3.7 Reference
### 5.4 Appendix D: condition system reference
#### 5.4.1 Restarts and related functions
##### Class RESTART
##### Function RESTART-NAME
##### Function COMPUTE-RESTARTS
##### Function FIND-RESTART
##### Function INVOKE-RESTART
##### Function INVOKE-RESTART-INTERACTIVELY
##### Examples
#### 5.4.2 Condition-restart association
##### Macro WITH-CONDITION-RESTARTS
##### Examples
#### 5.4.3 Restart macros
##### Macro RESTART-BIND
##### Macro RESTART-CASE
##### Macro WITH-SIMPLE-RESTART
##### Examples
#### 5.4.4 Standard restarts
##### Restart ABORT
##### Restart MUFFLE-WARNING
##### Restart CONTINUE
##### Restart STORE-VALUE
##### Restart USE-VALUE
##### Function ABORT, CONTINUE, MUFFLE-WARNING, USE-VALUE, STORE-VALUE
##### Examples
#### 5.4.5 Defining and instantiating conditions
##### Macro DEFINE-CONDITION
##### Function MAKE-CONDITION
##### Examples
#### 5.4.6 Assertions
##### Macro ASSERT
##### Macro CHECK-TYPE
##### Macro ECASE, ETYPECASE, CCASE, CTYPECASE
##### Examples
#### 5.4.7 Condition signaling
##### Function SIGNAL
##### Function WARN
##### Function ERROR
##### Function CERROR
##### Examples
#### 5.4.8 Handler macros
##### Macro HANDLER-BIND
##### Macro HANDLER-CASE
##### Macro IGNORE-ERRORS
##### Examples
#### 5.4.9 Condition types
##### Condition Type CONDITION
##### Condition Type WARNING
##### Condition Type STYLE-WARNING
##### Condition Type SERIOUS-CONDITION
##### Condition Type ERROR
##### Condition Type SIMPLE-CONDITION
##### Condition Type SIMPLE-WARNING
##### Condition Type SIMPLE-ERROR
##### Condition Type STORAGE-CONDITION
##### Condition Type TYPE-ERROR
##### Condition Type SIMPLE-TYPE-ERROR
##### Condition Type CONTROL-ERROR
##### Condition Type PROGRAM-ERROR
##### Condition Type CELL-ERROR
##### Condition Type UNBOUND-VARIABLE
##### Condition Type UNDEFINED-FUNCTION
##### Condition Type UNBOUND-SLOT
##### Condition Type STREAM-ERROR
##### Condition Type END-OF-FILE
##### Condition Type PARSE-ERROR
##### Condition Type READER-ERROR
##### Condition Type PACKAGE-ERROR
##### Condition Type FILE-ERROR
##### Condition Type PRINT-NOT-READABLE
##### Condition Type ARITHMETIC-ERROR
##### Condition Type DIVISION-BY-ZERO
##### Condition Type FLOATING-POINT-INVALID-OPERATION
##### Condition Type FLOATING-POINT-INEXACT
##### Condition Type FLOATING-POINT-UNDERFLOW
##### Condition Type FLOATING-POINT-OVERFLOW
##### Examples
#### 5.4.10 Debugger invocation
##### Variable \*BREAK-ON-SIGNALS\*
##### Variable \*DEBUGGER-HOOK\*
##### Function BREAK
##### Function INVOKE-DEBUGGER
##### Examples