☜	String Relations Draft MDC Standard					☞

7.2.2.3 String relations

The relations =, [, ], ]=, ]], and ]]= do not imply any numeric interpretation of either of their operands.

The relation = tests string identity. If the operands are not known to be numeric and numeric equality is to be tested, the programmer may apply an appropriate unary operator to the non-numeric operands. If both operands are known to be in numeric form (as would be the case, for example, if they resulted from the application of any operator except _), application of a unary operator is not necessary. The uniqueness of the numeric representation guarantees the equivalence of string and numeric equality when both operands are numeric. Note, however, that the division operator / may produce inexact results, with the usual problems attendant to inexact arithmetic.

The relation [ is called contains. A [ B is true if and only if B is a substring of A; that is, A [ B has the same value as ''$Find(A,B). Note that the empty string is a substring of every string.

The relation ] is called follows. A ] B is true if and only if A follows B in the sequence, defined here. A follows B if and only if any of the following is true.

1. B is empty and A is not.
2. Neither A nor B is empty, and the leftmost character of A follows (i.e., has a numerically greater $ASCII value than) the leftmost character of B.
3. There exists a positive integer n such that A and B have identical heads of length n, (i.e., $Extract( A , 1, n ) = $Extract( B , 1, n ) ) and the remainder of A follows the remainder of B (i.e., $Extract( A , n + 1, $Length(A) ) follows $Extract( B , n + 1, $Length(B) ) ).

The relation ]= is called follows or equals. A]=B is true if and only if A follows B as defined above or A is identical to B.

The relation ]] is called sorts after. A]]B is true if and only if A follows B in the subscript ordering sequence defined by the single argument $Order function as if that $Order refers to an lvn.

The relation ]]= is called sorts after or equals. A]]=B is true if and only if A sorts after B as defined above or A is identical to B.

The relation == tests object reference identity. A == B is true if and only if all of the following conditions are met:

1. The value of A has the data type OREF.
2. The value of B has the data type OREF.
3. A and B identify the same object.

In the context of the == operator, values are never coerced to any specific data type or interpretation.

Copyright © Standard Documents; 1977-2024 MUMPS Development Committee;
Copyright © Examples: 1995-2024 Ed de Moel;
Copyright © Annotations: 2003-2008 Jacquard Systems Research
Copyright © Annotations: 2008-2024 Ed de Moel.

Some specifications are "approved for inclusion in a future standard". Note that the MUMPS Development Committee cannot guarantee that such future standards will indeed be published.

This page most recently updated on 15-Nov-2023, 13:18:01.

For comments, contact Ed de Moel (demoel@jacquardsystems.com)