1 USING: alien arrays generic generic.math help.markup help.syntax
2 kernel math memory strings sbufs vectors io io.files classes
3 help generic.single continuations io.files.private listener
7 ARTICLE: "debugger" "The debugger"
8 "Caught errors can be logged in human-readable form:"
13 "User-defined errors can have customized printed representation by implementing a generic word:"
14 { $subsections error. }
15 "A number of words facilitate interactive debugging of errors:"
23 "Most types of errors are documented, and the documentation is instantly accessible:"
24 { $subsections :help }
25 "If the error was restartable, a list of restarts is also printed, and a numbered restart can be invoked:"
32 "You can read more about error handling in " { $link "errors" } "."
34 "Note that in Factor, the debugger is a tool for printing and inspecting errors, not for walking through code. For the latter, see " { $link "ui-walker" } "." ;
39 { $description "Prints the most recent error. Used for interactive debugging." } ;
42 { $description "Prints the data stack at the time of the most recent error. Used for interactive debugging." } ;
45 { $description "Prints the retain stack at the time of the most recent error. Used for interactive debugging." } ;
48 { $description "Prints the call stack at the time of the most recent error. Used for interactive debugging." } ;
51 { $values { "variable" "an object" } { "value" "the value, or f" } }
52 { $description "Looks up the value of a variable at the time of the most recent error." } ;
55 { $values { "n" "a positive integer" } }
56 { $description "Continues executing the " { $snippet "n" } "th restart. Since restarts may only be invoked once, this resets the " { $link restarts } " global variable." } ;
59 { $description "A shortcut for invoking the first restart." } ;
62 { $description "A shortcut for invoking the second restart." } ;
65 { $description "A shortcut for invoking the third restart." } ;
68 { $values { "error" "an error" } }
69 { $contract "Print an error to " { $link output-stream } ". You can define methods on this generic word to print human-readable messages for custom errors." }
70 { $notes "Code should call " { $link print-error } " instead, which handles the case where the printing of the error itself throws an error." } ;
73 { $values { "error" "an error" } { "topic" "an article name or word" } }
74 { $contract "Outputs a help article which explains the error." } ;
76 { error-help :help } related-words
79 { $values { "error" "an error" } }
80 { $description "Print an error to " { $link output-stream } "." }
81 { $notes "This word is called by the listener and other tools which report caught errors to the user." } ;
84 { $description "Print a list of restarts for the most recently thrown error to " { $link output-stream } "." } ;
87 { $values { "quot" "a quotation" } }
88 { $description "Attempts to call a quotation; if it throws an error, the error is printed to " { $link output-stream } ", stacks are restored, and execution continues after the call to " { $link try } "." }
90 "The following example prints an error and keeps going:"
92 "[ \"error\" throw ] try"
93 "\"still running...\" print"
95 { $link "listener" } " uses " { $link try } " to recover from user errors."
99 { $error-description "Thrown by " { $link alien-address } " and " { $link alien-invoke } " if an " { $link alien } " object passed in as a parameter has expired. Alien objects expire if they are saved an image which is subsequently loaded; this prevents a certain class of programming errors, usually attempts to use uninitialized objects, since holding a C address is meaningless between sessions." }
100 { $notes "You can check if an alien object has expired by calling " { $link expired? } "." } ;
103 { $error-description "Thrown by the C streams I/O primitives if an I/O error occurs." } ;
105 HELP: type-check-error.
106 { $error-description "Thrown by various primitives if one of the inputs does not have the expected type. Generic words throw " { $link no-method } " and " { $link no-math-method } " errors in such cases instead." } ;
108 HELP: divide-by-zero-error.
109 { $error-description "This error is thrown when " { $link / } " or " { $link /i } " is called with with a zero denominator." }
110 { $see-also "division-by-zero" } ;
114 "Thrown by the Factor VM when a Unix signal is received. While signal numbers are system-specific, the following are relatively standard:"
116 { "4 - Illegal instruction. If you see this error, it is a bug in Factor's compiler and should be reported." }
117 { "8 - Arithmetic exception. Most likely a divide by zero in " { $link /i } "." }
118 { "10, 11 - Memory protection fault. This error suggests invalid values are being passed to C functions by an " { $link alien-invoke } ". Factor also uses memory protection to trap stack underflows and overflows, but usually these are reported as their own errors. Sometimes they'll show up as a generic signal 11, though." }
120 "The Windows equivalent of a signal 11 is a SEH fault. When one occurs, the runtime throws a signal error, even though it does not correspond to a Unix signal."
123 HELP: array-size-error.
124 { $error-description "Thrown by " { $link <array> } ", " { $link <string> } ", " { $link <vector> } " and " { $link <sbuf> } " if the specified capacity is negative or too large." } ;
126 HELP: c-string-error.
127 { $error-description "Thrown by " { $link alien-invoke } " and various primitives if a string containing null bytes, or characters with values higher than 255 is passed in where a C string is expected. See " { $link "c-strings" } "." } ;
130 { $error-description "Thrown by " { $link dlopen } " and " { $link dlsym } " if a problem occurs while loading a native library or looking up a symbol. See " { $link "alien" } "." } ;
132 HELP: undefined-symbol-error.
133 { $error-description "Thrown if a previously-compiled " { $link alien-invoke } " call refers to a native library symbol which no longer exists." } ;
135 HELP: datastack-underflow.
136 { $error-description "Thrown by the Factor VM if an attempt is made to pop elements from an empty data stack." }
137 { $notes "You can use the stack effect tool to statically check stack effects of quotations. See " { $link "inference" } "." } ;
139 HELP: datastack-overflow.
140 { $error-description "Thrown by the Factor VM if an attempt is made to push elements on a full data stack." }
141 { $notes "This error usually indicates a run-away recursion, however if you legitimately need a data stack larger than the default, see " { $link "runtime-cli-args" } "." } ;
143 HELP: retainstack-underflow.
144 { $error-description "Thrown by the Factor VM if an attempt is made to access the retain stack in an invalid manner. This bug should never come up in practice and indicates a bug in Factor." }
145 { $notes "You can use the stack effect tool to statically check stack effects of quotations. See " { $link "inference" } "." } ;
147 HELP: retainstack-overflow.
148 { $error-description "Thrown by the Factor VM if " { $link dip } " is called when the retain stack is full." }
149 { $notes "This error usually indicates a run-away recursion, however if you legitimately need a retain stack larger than the default, see " { $link "runtime-cli-args" } "." } ;
152 { $error-description "Thrown by the Factor VM if an invalid memory access occurs." }
153 { $notes "This can be a result of incorrect usage of C library interface words, a bug in the compiler, or a bug in the VM." } ;
155 HELP: primitive-error.
156 { $error-description "Thrown by the Factor VM if an unsupported primitive word is called." } ;