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.
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 Reserved Keywords.
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