Implementation of SUBSTR() command

this is a standard DMIS 5.2 command able to extract a substring from a string.

The command is:

SUBSTR(str,x var_8) 

Where:

str: is the string to be tested
x: is the position where to start
y: is the position where to stop (this is an optional parameter, if missing the string is extracted to the end)

An example of use is:

DECL/CHAR,100,str1,str2
str1=ASSIGN/'My full String'
$$reading the string from char #4 to char #7
str2=ASSIGN/SUBSTR(str1,4,7)