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throw. Execute throw Control

Valid only inside an explicit definition.

Causes execution to resume after catcht. in a higher-level function.

throw. terminates the current explicit definition with an uncaught throw. error. Execution resumes in the caller:

  1. If the caller is executing in a try. control that has a catcht., the error is cleared and execution continues at the line following the catcht.
  2. Otherwise, the caller terminates with the uncaught throw. error, and execution continues in its caller, continuing the search for an active catcht. . Calling functions are terminated one by one until catcht. is encountered.

If no calling function contains an active catcht., J returns to immediate mode with the uncaught throw. error.

throw. may be thought of as a special type of error that is not intercepted by catch. or u :: v.

Common Uses

1. Return a noun from sub without signalling an error and execute a given B-block in its caller: main

main=: 3 : 0   NB. calls: sub
  sub y
  select. type_jthrow_
   case. 'aaaa' do. 'throw aaaa'  
   case. 'bbb'  do. 'throw bbb'   
   case. 'cc'   do. 'throw cc' 
   case.        do. throw.   NB. handled by a higher-level catcht. (if any)

sub=: 3 : 0
 if. y<0 do. type_jthrow_=: 'aaaa' throw. end.
 if. y<4 do. type_jthrow_=: 'bbb'  throw. end.
 if. y<8 do. type_jthrow_=: 'cc'   throw. end.
 (":y),' not thrown'

   main _4
throw aaaa
   main 1
throw bbb
   main 5
throw cc
   main 88
88 not thrown

NOTE: throw. can communicate information back to its target catcht.. via a global name in a given locale, e.g. type_jthrow_ above.