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| Constants and macros | |||||
If you are repeating a section of code or text multiple times in a program, you might want to create a macro to simplify program creation and maintenance.
Essentially, a macro is just a method for creating a shorthand reference that will later be replaced by a larger piece of code or text as specified in the macro definition. For example, if you want to include a piece of debugging code or if you are repeating the name of a company multiple times in a program, you could create a macro that contains that code or company name, and instead of typing the full text or code every time you need it, you could simply use the shorthand version that you have defined in the macro. Not only does this reduce the time required to create a program (by cutting down on typing), it also reduces the number of potential typos. Additionally, if the code or the name of the company should change, rather than searching through an entire program to replace each occurrence, you need only change the text contained in the macro, and it will automatically be changed in the rest of the program.
A macro is created using the macro and macro-end keywords. The macro-end keyword is required because a macro can contain any text or code, so there is no other way for the program to know where the macro definition ends and the rest of the program begins. The following macro definition creates a shorthand reference for the company name "OmniMark":
macro om is
"OmniMark"
macro-end
All this does is tell the program that every time it encounters the short form "om", it's supposed to replace that short form with the full text OmniMark.
Although the following macro definition looks significantly more complex, the basic principles are the same:
; Macro to dump a switch shelf (for debugging purposes)
;
macro Dump Switch token s is
do
output "Switch %@(s) has " || "d" format number of s || " items%n"
repeat over s
output " %@(s) @ %d(#item)"
output " ^ " || key of s when s is keyed
output " = "
do when s
output "true"
else
output "false"
done
output "%n"
again
done
macro-end
This macro will replace each occurrence of the macro name "Dump Switch" with the code that appears between the keywords "is" and "macro-end" in the macro definition.
Once defined, macros are very simple to use. For example, the following program will output "Welcome to OmniMark. OmniMark is located in Ottawa, Ontario, Canada.":
macro om is
"OmniMark"
macro-end
process
output "Welcome to " || om || ". "
output om || " is located in Ottawa, Ontario, Canada.%n"
Macros don't have to be exact repetitions of a chunk of text. Macros can take "arguments", which are simply values given to the macro and used to change slightly the text that replaces the shorthand reference. The macro "Switch Dump", shown above, takes one token argument ("s").
One thing to note about macros is that all macro references are replaced with the full text of the macro before the program is compiled and run. What this means is that if you are using OmniMark LE, defining a section of code in a macro won't cut down on the total number of actions that appear in your program. Each time a macro is used, any actions contained in that macro are counted. So, if you define a macro that contains two actions and you use that macro five times in a program, it will count as ten actions towards the total number of actions in the program.
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