# Railroad

Grammar rules drawn as railroad tracks. Mermaid marks this type as beta.

## Examples

The playground samples for this type, rendered by Ondine when the documentation builds.

### Example 1

```mermaid
railroad-ebnf-beta
title "Arithmetic Expression Grammar"

expression = term ( ( "+" | "-" ) term )* ;
term = factor ( ( "*" | "/" ) factor )* ;
factor = number | "(" expression ")" ;
number = digit+ ;
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;

```

### Example 2

```mermaid
railroad-ebnf-beta
title "JSON Grammar"

json = element ;
element = object | array | string | number | "true" | "false" | "null" ;
object = "{" [ member ( "," member )* ] "}" ;
array = "[" [ element ( "," element )* ] "]" ;
member = string ":" element ;

```

### Example 3

```mermaid
railroad-abnf-beta
title "Email Address"

address = local-part "@" domain ;
local-part = 1*( ALPHA / DIGIT / "." / "-" ) ;
domain = label *( "." label ) ;
label = 1*( ALPHA / DIGIT / "-" ) ;

```

### Example 4

```mermaid
railroad-peg-beta
title "Calculator Grammar"

Expression <- Term (("+" / "-") Term)* ;
Term <- Factor (("*" / "/") Factor)* ;
Factor <- Number / "(" Expression ")" ;
Number <- Digit+ ;
Digit <- "0" / "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9" ;

```

### Example 5

```mermaid
railroad-peg-beta
title "Identifiers (keywords excluded)"

Identifier <- !Keyword Letter Letter* ;
Keyword <- "if" / "else" / "while" ;
Letter <- "a" / "b" / "c" / "_" ;

```

### Example 6

```mermaid
railroad-beta
title Expression Grammar

expression = sequence(
    nonterminal("term"),
    zeroOrMore(sequence(
        choice(terminal("+"), terminal("-")),
        nonterminal("term")
    ))
) ;
term = sequence(
    nonterminal("factor"),
    zeroOrMore(sequence(
        choice(terminal("*"), terminal("/")),
        nonterminal("factor")
    ))
) ;
factor = choice(
    nonterminal("number"),
    sequence(terminal("("), nonterminal("expression"), terminal(")"))
) ;
number = oneOrMore(nonterminal("digit")) ;
digit = choice(terminal("0"), terminal("1"), terminal("2"), terminal("3"), terminal("4"), terminal("5"), terminal("6"), terminal("7"), terminal("8"), terminal("9")) ;

```