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WritingGrammars.md

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Quick guide for write grammars

Hi!

You want to write a grammar quickly

Let's begin

Rules

The rules are the way to define a sentence

// name = {"something"}
organization = {"IETF means Internet Engineering Task Force"}

A rule can refer to more rules

browser = {"Firefox"}
fact = {browser ~ " has a good performance."}

// prints: "Firefox has a good performance."

Ordered choices

You can have multiple options with "|"

browser = {"Firefox" | "Chrome" | "Safari"}
fact = {browser ~ " has a good support."}

// "Firefox has a good support."
// "Chrome has a good support."
// "Safari has a good support."

Options

You can generate something or not... with "?"

evasion = "don't"
sentence = {"I " ~ evasion? ~ " like to clean my room."}

// {"I like to clean my room."}
// {"I don't like to clean my room."}

Repetitions

You can repeat a rule n times with {n}

uncontrollable = {" great"}
fact = {"I have a" ~ uncontrollable{3} ~ " desire to eat hamburger."}

// "I have a great great great desire to eat hamburger."

You can repeat a rule in a range with {n,m} [inclusive, inclusive]

uncontrollable = {" great"}
fact = {"I have a" ~ uncontrollable{2,4} ~ " desire to eat hamburger."}

// "I have a great great desire to eat hamburger."
// "I have a great great great desire to eat hamburger."
// "I have a great great great great desire to eat hamburger."

You can repeat a rule at most n times with {,n}, it's like {0, n}

uncontrollable = {" great"}
fact = {"I have a" ~ uncontrollable{,3} ~ " desire to eat hamburger."}

// "I have a desire to eat hamburger."
// "I have a great desire to eat hamburger."
// "I have a great great to eat hamburger."
// "I have a great great great desire to eat hamburger."

You can repeat a rule at least n times with {n,}, it's like {n, infinity} (Not really, but there are an option to control the upper limit)

uncontrollable = {" great"}
fact = {"I have a" ~ uncontrollable{,3} ~ " desire to eat hamburger."}

// "I have a desire to eat hamburger."
// "I have a great desire to eat hamburger."
// "I have a great great to eat hamburger."
// "I have a great great great desire to eat hamburger."

You can repeat a rule zero or more times with *, it's like {0, infinity} (Not really, but there are an option to control the upper limit)

uncontrollable = {" great"}
fact = {"I have a" ~ uncontrollable* ~ " desire to eat hamburger."}

// "I have a desire to eat hamburger."
// "I have a great desire to eat hamburger."
// ...
// "I have a great great great great desire to eat hamburger."

You can repeat a rule one or more times with *, it's like {1, infinity} (Not really, but there are an option to control the upper limit)

uncontrollable = {" great"}
fact = {"I have a" ~ uncontrollable+ ~ " desire to eat hamburger."}

// "I have a great desire to eat hamburger."
// ...
// "I have a great great great great desire to eat hamburger."

Grouping

You can group things with parentheses "(" and ")"

// aerobics will have a probability of 0.25 to be generated.
// archery will have a probability of 0.25 to be generated.
// cycling will have a probability of 0.5 to be generated.
sport = {("aerobics" | "archery") | "cycling"}
sentence = {"I like to do " ~ sport ~ " in the mornings."}

The negation predicate

You can avoid the generation of an element with this pattern

// Or letter = {ASCII_ALPHA_LOWER}
letter = { "a" | "b" | "c" | "d" | "e" | "f" | "g" }
vocal = { "a" | "e" | "i" | "o" | "u"}

consonant = {!vocal ~ letter}

The only constraint to use this is that the exclamation point must be accompanied by a rule

// This is valid, but doesn't work

consonant = {!("a" | "e" | "i" | "o" | "u") ~ letter}

Char ranges

You can define a range of characters like this:

letter = { 'a'..'z' }
other = {'b'..'m'}
hex = {'A'..'F'}

Built-in rules

There are rules available for simplify the grammar

Note: Currently only the ascii rules from pest reference are supported.

Rule Equivalent
ANY ('\u{00}'..'\u{10FFFF}')
ASCII_DIGIT ('0'..'9')
ASCII_NONZERO_DIGIT ('1'..'9')
ASCII_BIN_DIGIT ('0'..'1')
ASCII_OCT_DIGIT ('0'..'7')
ASCII_HEX_DIGIT `('0'..'9'
ASCII_ALPHA_LOWER ('a'..'z')
ASCII_ALPHA_UPPER ('A'..'Z')
ASCII_ALPHANUMERIC ('0'..'9' 'a'..'z' | 'A'..'Z')
NEWLINE `("\n" 
number = {ASCII_DIGIT}

// Some day
myWage = ASCII_NONZERO_DIGIT{5,10}

secretMessage = ASCII_ALPHANUMERIC+