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Chapter 13. Keyword Instructions
A keyword instruction is one or more clauses, the first of which starts with a keyword that identifies the
instruction. Some keyword instructions affect the flow of control, while others provide services to the
programmer. Some keyword instructions, like DO, can include nested instructions.
In the syntax diagrams on the following pages, symbols (words) in capitals denote keywords or
subkeywords; other words (such as expression) denote a collection of tokens as defined previously. Note,
however, that the keywords and subkeywords are not case dependent; the symbols if, If, and iF all have
the same effect. Note also that you can usually omit most of the clause delimiters (;) shown because they
are implied by the end of a line.
As explained in section “Keyword Instructions” on page 120, a keyword instruction is recognized only if its
keyword is the first token in a clause, and if the second token does not start with an = character (implying
an assignment) or a colon (implying a label). The keywords ELSE, END, OTHERWISE, THEN, and WHEN
are recognized in the same situation. Note that any clause that starts with a keyword defined by REXX
cannot be a command. Therefore,
arg(fred) rest
is an ARG keyword instruction, not a command that starts with a call to the ARG built-in function. A syntax
error results if the keywords are not in their correct positions in a DO, IF, or SELECT instruction. (The
keyword THEN is also recognized in the body of an IF or WHEN clause.) In other contexts, keywords are
not reserved and can be used as labels or as the names of variables (though this is generally not
recommended).
Certain other keywords, known as subkeywords, are reserved within the clauses of individual instructions.
For example, the symbols VALUE and WITH are subkeywords in the ADDRESS and PARSE instructions,
respectively. For details, see the description of each instruction. For a general discussion on reserved
keywords, see page 409.
Blanks adjacent to keywords have no effect other than to separate the keyword from the subsequent
token. One or more blanks following VALUE are required to separate the expression from the subkeyword
in the example following:
ADDRESS VALUE expression
However, no blank is required after the VALUE subkeyword in the following example, although it would
add to the readability:
ADDRESS VALUE'ENVIR'||number
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