System Function ES

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Quad ES - Event Simulate - ⎕ES     System Function

Event Simulate [with either Error Message(⎕EM) or Event Type(⎕ET)] - for debugging, user alerts, detailed at-length error messaging purposes.

Monadic Function

⎕ES R
R may frequently be one of three distinct Cases: 1) Simple character scalar or vector; 2) Simple two-item vector of integers, 'normally' between -32767 and 32767; or 3) An empty vector.
⎕ES does not have a Z type return argument. It's effect on the APL interpreter is to show on the user's display, certain debugging information, depending on how the call to ⎕ES was made.


Quad ES ⎕ES Event Simulate - sample monadic use/user session(with comments using ⍝ symbol): 

      ⎕VR 'ErrorSim'  ⍝Virtual representation of user-function ErrorSim. It has one right argument, A.
    ∇ ErrorSim A
[1]   ⍝Simulate an error.  If the test (next line, just below) inside the parentheses evaluate to True then Event IS simulated.
[2]   ⎕ES(0=A)/'ZERO INVALID'  ⍝Event Simulate occurs here, if A=0 then a user/SysOp error message will appear(in System Variable ⎕EM).
[3]   '⎕ET(Event Type) = ',⎕ET   ⍝ ⎕ES frequently affects sys var quad Event Type ⎕ET, although not presently in NARS.
[4]   '⍴⎕EM(Error Message) = ',(⍴⎕EM),'  ⎕EM:'   ⍝ ⎕EM IS affected in NARS - IF the Error Condition evaluate to True(1).
[5]   ⎕EM
    ∇ 2015 2 20 22 31 5 647 (UTC)

      ErrorSim 45     ⍝ <<< In this event simulation(user types in ErrorSim 45), there should be NO EFFECT since 45 is not equal to 0.
⎕ET(Event Type) =  0 0  ⍝ As mentioned ⎕ET remains unaffected = {0 0}
⍴⎕EM(Error Message) =  3 0   ⎕EM:   ⍝ Since there was NO error(no event simulation) ⎕EM is also unaffected - it has 3 empty rows(0 cols).

      ErrorSim 0    ⍝ <<< In this event simulation(user types in ErrorSim 0); there SHOULD BE an EFFECT; A = 0 (test evaluates to True).
ZERO INVALID        ⍝ Sure enough, the Error Message ⎕EM is returned by NARS/APL with ⎕EM = 'ZERO INVALID'
      ErrorSim 0    ⍝ Normally APL would also return the user-function line number which 'failed' here ⎕ES returns zero.
      ∧
      ⎕EM          ⍝ Sure enough, ⎕EM when typed in by user, shows the most recent simulated error message from ⎕ES.
ZERO INVALID    
      ErrorSim 0
      ∧         
      ⎕ET          ⍝ Also note that ⎕ET was not affected even though in some APL implementations ⎕ES can/will affect ⎕ET.
0 0

When is ⎕ES useful?

  • You want to specifically get the user's attention when a certain error, input error, or other frequent error condition can/could occur.
  • You want to show a More Detailed Error Message when a known error occurs.
  • You are debugging a certain area of APL user-function code and want to test simulating the error condition(s).
  • Since program/code suspension occurs at the CALLING POINT, not within the defined operation/user function per se, it translates to more focus on the input or arguments which may have caused/triggered the event to occur.
  • It can be used, for example, to generate various return codes on system resource limitations encountered, see ⎕ET.

Dyadic Function

Not Currently Documented - Although Dyadic Event Simulate ⎕ES Use is implemented in some APL versions.


Note: ⎕ES is available as both a monadic and dyadic form system function, you cannot assign a value to it.

System Variables (A value may be assigned to these except for ⎕DM)
⎕ALX ⎕CT ⎕DM ⎕DT ⎕ELX ⎕FC ⎕FEATURE ⎕FPC ⎕IC ⎕IO
⎕LR ⎕LX ⎕PP ⎕PR ⎕PW ⎕RL ⎕SA ⎕WSID
Niladic System Functions (a value cannot be assigned to these)
⎕A ⎕AV ⎕EM ⎕ET ⎕LC ⎕NNAMES ⎕NNUMS ⎕SI ⎕SYSID ⎕SYSVER
⎕T ⎕TC ⎕TCBEL ⎕TCBS ⎕TCESC ⎕TCFF ⎕TCHT ⎕TCLF ⎕TCNL ⎕TCNUL
⎕TS ⎕WA
Monadic or dyadic system functions (a value cannot be assigned to these)
⎕AT ⎕CR ⎕DC ⎕DFT ⎕DL ⎕DR ⎕EA ⎕EC ⎕ERROR ⎕ES
⎕EX ⎕FMT ⎕FX ⎕MF ⎕NAPPEND ⎕NC ⎕NCREATE ⎕NERASE ⎕NINFO ⎕NL
⎕NLOCK ⎕NREAD ⎕NRENAME ⎕NREPLACE ⎕NRESIZE ⎕NSIZE ⎕NTIE ⎕NUNTIE ⎕STOP ⎕TF
⎕TRACE ⎕UCS ⎕VR
Note that quad functions and variables (except for the ⎕A family of functions) are case insensitive


See Also
System Commands System Variables and Functions Operators


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