parsing expression grammar, aka parsing expression grammar, is a historical grammar language created in 2002.

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Example code from the web:

Expr    ← Sum
Sum     ← Product (('+' / '-') Product)*
Product ← Value (('*' / '/') Value)*
Value   ← [0-9]+ / '(' Expr ')'

Example code from Wikipedia:

Value   ← [0-9.]+ / '(' Expr ')'
Product ← Expr (('*' / '/') Expr)*
Sum     ← Expr (('+' / '-') Expr)*
Expr    ← Product / Sum / Value
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Last updated February 11th, 2019