`gen-text`

Description

A generator of random texts from EBNF-like grammars.

Install

Install Ruby 1.9.3 or higher.
gem install gen-text

Example

Simple grammar:

expr =
  expr ('+'|'-') expr |
  expr ('*'|'/') expr |
  '(' expr ')' |
  0...1000 ;

Sample output:

(914-548*155+131*799)*827

See more examples in "sample" directory.

Usage

Run it with the command:

gen-text file.g

Here file.g is a file containing the grammar description which consists of the rule definitions:

nonterminal1 = expr1 ;

nonterminal2 = expr2 ;

nonterminal3 = expr3 ;

Nonterminals start from a letter or "_" and may contain alphanumeric characters, "_", "-" and ":".

You may also use backquoted nonterminals:

`nonterminal1` = expr1 ;

`Nonterminal with arbitrary characters: [:|:]\/!` = expr2 ;

Trailing ";" can be omitted:

nonterminal1 = expr1

nonterminal2 = expr2

nonterminal3 = expr3

Also you may omit the left part in the first rule:

expr1

nonterminal2 = expr2

nonterminal3 = expr3

You may use C++-like comments:

// A comment

/* Another comment */

Expressions

You may use the following expressions in the rules' right part:

Expression	Meaning
`"str"` `'str'`	Generate a string. Following escape sequences are allowed: "\n", "\t", "\e" and "\." where "." is an arbitrary character.
`U+HHHH`	Generate an UTF-8 character sequence corresponding to the Unicode code. E. g.: `U+000A` is equivalent to `"\n"`.
`n` (a number)	Generate a number
`m...n`	Generate a random number between `m` and `n` (inclusive).
`nonterm`	—
Combinators
`expr expr`	Sequence.
`expr \| expr`	Random choice.
`\| expr \| expr`	Random choice (another form).
`\| [m%] expr \| [n%] expr \| expr`	Random choice with specific probabilities. If probability is unspecified then it is calculated automatically.
`\| [0.1] expr \| [0.3] expr \| expr`	The same as above. Probabilities may be specified as floating point numbers between 0.0 and 1.0.
`expr` `expr+` `expr?` `expr[n]` `expr*[m...n]`	Repeat `expr` many times: 0 or more times 1 or more times 0 or 1 time exactly `n` times between `m` and `n` times Note: you may use `inf` ("infinity") instead of `m` or `n`.
`n:expr`	Capture a string generated by `expr` into variable `n`. The variable may then be used in Ruby code insertions. You may also use names like `$n` and `@n`. Note: presence of this expression turns on backtracking and output buffering and may result in enormous memory usage.
`n := expr`	The same as above but the output generated by `expr` is discarded.
Ruby code insertions
`{ code }`	Execute the code. Generate nothing. Note: all code insertions inside a rule share the same scope.
`{= code }`	Generate a string returned by the code.
`{? code }`	Condition. A code which must evaluate to true. Note: presence of this expression turns on backtracking and output buffering and may result in enormous memory usage.

Alternate syntax

You may use "<-" instead of "=":

nonterm1 <- expr1 ;

nonterm2 <- expr2 ;

and "/" instead of "|":

`simple choice` <- "a" / "b" ;

gen-text