October 2024
Intermediate to advanced
272 pages
6h 54m
English
Content preview from Seven Obscure Languages in Seven Weeks
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Controlling Execution Flow
m4 macros can function as global variables when expanded without arguments or as functions when arguments are provided. In both cases, m4 can use the existence of a macro to control program execution flow.
Conditional Expansion
The built-in macro ifdef(name,true_string,false_string) tests if the macro name is defined and expands to true_string or false_string, depending on the outcome.
With this macro, you can reorganize the code fragment to focus on the decision (ACCEPT vs. REJECT) and define the MOOD and STATUS appropriately.
| | divert(-1) |
| | define(`AUTHOR', Alice) |
| | define(`MANUSCRIPT', My Friend Bob) |
| | |
| | # The status of the manuscript |
| | define(`ACCEPT') |
| | define(`MOOD', ifdef(`ACCEPT',happy,sorry)) ... |
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