This section includes parsing several strings and flow charts illustrating a conceptual view of parsing.
Only ARG and PARSE ARG can have more than one source string. To parse several strings, you can specify several comma-separated templates. Here is an example:
parse arg template1, template2, template3
This instruction consists of the keywords PARSE ARG and three comma-separated templates. For an ARG instruction, the source strings to be parsed come from arguments you specify when you call a program or CALL a subroutine or function. Each comma is an instruction to the parser to move on to the next string.
/* Parsing several strings in a subroutine */ num="3" musketeers="Porthos Athos Aramis D'Artagnan" CALL Sub num,musketeers /* Passes num and musketeers to sub */ SAY total; say fourth /* Displays: "4" and " D'Artagnan" */ EXIT Sub: parse arg subtotal, . . . fourth total=subtotal+1 RETURN
Note that when a Rexx program is started as a command, only one argument string is recognized. You can pass several argument strings for parsing if:
One Rexx program calls another Rexx program with the CALL instruction or a function call
Programs written in other languages start a Rexx program
If there are more templates than source strings, each variable in a leftover template receives a null string. If there are more source strings than templates, the language processor ignores leftover source strings. If a template is empty (two subsequent commas) or contains no variable names, parsing proceeds to the next template and source string.
There is a special case in which absolute and relative positional patterns do not work identically. Parsing with a template containing a string pattern skips the data in the source string that matches the pattern (see Templates Containing String Patterns). But a template containing the sequence string pattern, variable name, and relative position pattern does not skip the matching data. A relative positional pattern moves relative to the first character matching a string pattern. As a result, assignment includes the data in the source string that matches the string pattern.
/* Template containing string pattern, then variable name, then */ /* relative positional pattern does not skip any data. */ string="REstructured eXtended eXecutor" parse var string var1 3 junk "X" var2 +1 junk "X" var3 +1 junk say var1||var2||var3 /* Concatenates variables; displays: "Rexx" */
Here is how this template works:
The following figures are to help you understand the concept of parsing.
The figures include the following terms:
is the beginning of the source string (or substring).
is the end of the source string (or substring).
is the length of the source string.
is in the source string and is the first character of the match.
is in the source string. For a string pattern, it is the first character after the end of the match. For a positional pattern, it is the same as match start.
is in the source string. For a string pattern, it is the first matching character. For a positional pattern, it is the position of the matching character.
is a distinct syntactic element in a template, such as a variable, a period, a pattern, or a comma.
is the numeric value of a positional pattern. This can be either a constant or the resolved value of a variable.
Note: The figures do not include error cases.