The -errorinfo return option of an interpreter is used to accumulate a stack trace of what was in progress when an error occurred; as nested commands unwind, the Tcl interpreter adds information to the -errorinfo return option. If the info argument is present, it is used to initialize the -errorinfo return options and the first increment of unwind information will not be added by the Tcl interpreter. In other words, the command containing the error command will not appear in the stack trace; in its place will be info. Historically, this feature had been most useful in conjunction with the catch command: if a caught error cannot be handled successfully, info can be used to return a stack trace reflecting the original point of occurrence of the error:
catch {...} errMsg
set savedInfo $::errorInfo
...
error $errMsg $savedInfo
When working with Tcl 8.5 or later, the following code should be used instead:
catch {...} errMsg options
...
return -options $options $errMsg
If the code argument is present, then its value is stored in the -errorcode return option. The -errorcode return option is intended to hold a machine-readable description of the error in cases where such information is available; see the return manual page for information on the proper format for this option's value.
if {1+2 != 3} {
error "something is very wrong with addition"
}