System Variable IC

⎕IC - Indeterminate Control

Z←⎕IC returns the current value of the Indeterminate Control Vector.

Z is an integer vector whose elements each control a separate aspect of how indeterminates are handled by the system.

⎕IC←R sets all of the values of the Indeterminate Control Vector to R. ⎕IC←⍬ sets all of the values of the Indeterminate Control Vector to their system default state. ⎕IC[L]←R sets the value(s) of the Indeterminate Control Vector indexed by L to R.

This experimental feature attempts to collect together in one place control of various infinite and indeterminate calculations such as ÷0, 0÷0, and friends. The values of this multi-element vector each control a different calculation. In particular,

⎕IC Index (origin-0)	Indeterminate Calculation	Default Result
0	÷0	∞
1	⍟0	¯∞
2	!N for integer N<0	DOMAIN ERROR
3	0×∞ or ∞×0	DOMAIN ERROR
4	0ׯ∞ or ¯∞×0	DOMAIN ERROR
5	0÷0	1
6	∞÷∞ (same sign)	DOMAIN ERROR
7	∞÷∞ (different sign)	DOMAIN ERROR
8	∞-∞ (same sign)	DOMAIN ERROR
9	L|±∞	DOMAIN ERROR
10	0*0	1
11	L*∞ for any L≤¯1	DOMAIN ERROR
12	0⍟0	DOMAIN ERROR
13	0⍟1	DOMAIN ERROR
14	1⍟0	DOMAIN ERROR
15	1⍟1	1
16	0*∞	0
17	0*¯∞	∞
18	±∞*0	DOMAIN ERROR
19	0∨±∞ or ±∞∨0	DOMAIN ERROR
20	0∧±∞ or ±∞∧0	DOMAIN ERROR

The values in each element of ⎕IC control the result of the calculation as follows:

⎕IC Value	Result
¯1	¯1
0	0
1	1
2	DOMAIN ERROR
3	∞
4	¯∞

For example,

      ⎕IO←0
      ⎕IC
3 4 2 2 2 1 2 2 2 2 1 2 1 2 2 1 0 3 2 2 2
      0÷0
1
      ⎕IC[5]←2
      0÷0
DOMAIN ERROR
      0÷0
       ∧
      ⎕IC←⍬
      ⎕IC
3 4 2 2 2 1 2 2 2 2 1 2 1 2 2 1 0 3 2 2 2

To set all indeterminate results to DOMAIN ERROR, use ⎕IC[]←2.

Incomplete List of Indeterminates

That there may be other indeterminates not covered by this feature. Please let us know if you think there are other cases that should be included.

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