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# shelf_inc(+ShelfHandle, +Index)

Increment an integer slot within a shelf object

ShelfHandle
  A shelf handle or shelf name
Index
  An integer

## Description

This looks up the entry in the Index'th slot of the shelf object denoted by ShelfHandle, and if such an entry exists, and is of integer type, it is incremented by one. This predicate is a shorthand for:

    	shelf_inc(ShelfHandle, Index) :-
    	    shelf_get(ShelfHandle, Index, C0),
    	    C1 is C0 + 1,
    	    shelf_set(ShelfHandle, Index, C1).

The slots are numbered from 1 to the maximum which was determined during shelf creation (but note that ECLiPSe's struct-syntax can be used to give the slots symbolic names, see struct/1).

Note: If ShelfHandle is not a handle, then it must be an atom or a compound term, and the shelf is identified by this term's toplevel functor together with the context module.

### Modes and Determinism

- shelf_inc(+, +) is det

### Modules

This predicate is sensitive to its module context (tool predicate, see @/2).

### Exceptions

(4) instantiation fault
  ShelfHandle is not instantiated
(5) type error
  Index is not instantiated
(5) type error
  ShelfHandle is not a shelf
(5) type error
  Index is not an integer
(6) out of range
  Index is less than 1 or greater than the number of slots on the shelf
(6) out of range
  The counter value exceeds an implementation-defined limit (at least 2^31)
(40) stale object handle
  ShelfHandle refers to an already destroyed shelf

## Examples

    For examples see shelf_create/2,3.

## See Also

shelf_create / 2, shelf_create / 3, shelf_dec / 2, shelf_set / 3, shelf_abolish / 1, struct / 1