# Macros

Macros allow you to create polymorphic rules:

# Matches "'Hello?' 'Hello?' 'Hello?'"
matchThree[X] -> $X " " $X " " $X
inQuotes[X] -> "'" $X "'"

main -> matchThree[inQuotes["Hello?"]]
 
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Macros are dynamically scoped, which means they see arguments passed to parent macros:

# Matches "Cows oink." and "Cows moo!"
sentence[ANIMAL, PUNCTUATION] -> animalGoes[("moo" | "oink" | "baa")] $PUNCTUATION
animalGoes[SOUND] -> $ANIMAL " " $SOUND # uses $ANIMAL from its caller

main -> sentence["Cows", ("." | "!")]
 
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Macros are expanded at compile time and inserted in places they are used. They are not "real" rules. Therefore, macros cannot be recursive (nearleyc will go into an infinite loop trying to expand the macro-loop). They must also be defined before they are used (except by other macros).