Miscellaneous Operators

The exec keyword or $ operator is very useful. It equates its operand. So, for example, a string containing a valid equate expression could be given as an argument to this operator which would then execute the string as an equate returning any value resulting. For example, here is a definition of strlen (called gstrlen) for any database field.

%%EQUATE gstrlen
  inputs(str)
  outputs(strlen(exec(str)))

The function might be called with gstrlen(%%NAME). Note that the %% operator is used to put the field name on the stack. Then within the function the $ operator is used to evaluate the argument as an equate expression, thus getting the contents of the field.

There is no dynamic array support in equate expressions currently, but a simplified mechanism can be written using the exec operator to create named variables with a numeric index to simulate this. The size of an array would be limited to a few hundred elements (or less, depending on how much local variable space is available on the stack). The example below defines aget to get the contents of an array element and aput to assign a value to an array element and example to show the equates being used. The definitions below use global variables and work only with string values.

%%EQUATE aget(name,index)
  "" >> index_str
  index >> index_str
  exec("_"+name+index_str)
%%EQUATE aset(name,index,value)
  "" >> index_str
  index >> index_str
  exec(value+">>_"+name+index_str)
%%EQUATE example
  /* create 5 element array, each element is set to "hello" */
  0 >> i
  while i < 5 do aset("ex",i,"hello") ++i >> i wend
  /* read back contents of array, send to stdout */
  0 >> i
  while i < 5 do aget("ex",i) write ++i >> i wend

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