## Expand description

## glc

This crate’s aim is to generate random expressions based on a context-free grammar.

The acronym stands for “gramática livre de contexto” (*context-free grammar*).

### How to Use

```
use glc::{Grammar, t_or_rule, nt_seq_rule};
let grammar = Grammar(
// starting symbol
"S".into(),
// vector of rules
vec![
// a rule that generates a sequence of non-terminals: "A B"
nt_seq_rule!("S" => "A", "B"),
nt_seq_rule!("B" => "A", "B", "N"),
nt_seq_rule!("B" => "E"),
t_or_rule!("E" => ""),
// a rule that is an "or" of terminals: any letter from a-z
t_or_rule!(
"A" => "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k",
"l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v",
"w", "x", "y", "z"
),
t_or_rule!("N" => "0", "1", "2", "3", "4", "5", "6", "7", "8", "9"),
],
);
// generate a random string with this grammar
println!("{}", grammar.gen());
```

A simplified version of the macro above is available:

```
// You may need to tune this parameter depending on how large is your grammar,
// since the `grammar` macro is recursive.
#![recursion_limit = "256"]
use glc::grammar;
let _grammar = grammar!{
// The first non-terminal seen (head of the 1st rule) will be
// the starting symbol (in this case: `S`).
S => A B;
B => A B N;
B => E;
E => "";
// Or transform a non-terminal in one among many terminals
A => "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k",
"l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v",
"w", "x", "y", "z";
N => "0", "1", "2", "3", "4", "5", "6", "7", "8", "9"
};
```

For a real-life example take a look at mexe.

### Links

## Macros

- Generate a grammar using the following syntax:
- Represents a rule that replaces one non-terminal by a sequence of non-terminals. Invoke it like this:
- Parse a rule.
- Represents a disjunctive rule: a non-terminal that can be replaced by one of the listed terminal symbols. An invocation of this macro looks like this:

## Structs

- A derivation starts with the starting non-terminal symbol of the grammar and progresses by iteratively replacing non-terminals by some sequence of symbols, according to the grammar rules.
- An expression constituted of a sequence of terminal symbols. These expressions can be obtained by making a complete
`Derivation`

with the`Grammar`

. A`Derivation`

that has only terminal symbols can be converted into an expression. - Represents a context-free grammar. Contains a
`NonTerminal`

which represents the starting symbol and a list of`Rule`

s. - A non-terminal symbol is a symbol that must be replaced further before the final expression is complete.
- A disjunction of
`Sequence`

s. - Represents a grammar rule. Contains a
`NonTerminal`

which represents the rule’s head, and a`RuleBody`

. - A sequence of
`Symbol`

s. - A terminal symbol is a symbol that is not further replaceable. It can appear in the final expression generated.

## Enums

- A
`Symbol`

can be a`Terminal`

(a symbol that can appear in the final expression generated by the grammar) or a`NonTerminal`

(a symbol that must be replaced further).