simpar

A simple declarative string parser using string operations from the standard library.

The parse! macro allows you to extract variables from strings based on specified patterns, with support for type conversion and various separators.

For example, if s is a string of the form "<name> <age> birthday: <day>.<month>.<year>" then name, age and the birthday can be retrieved with:

use simpar::parse;

let s = "Alice 42 birthday: 1.1.1970";

parse!(s -> name, age: u8, _, day.month.year);

assert_eq!(name, "Alice");
assert_eq!(age, 42);
assert_eq!((day, month, year), ("1", "1", "1970"));

Pattern Syntax Reference

A pattern consists of matches (usually identifiers) followed by separators. Valid matches are:

• <var> - capture as string slice and assign it to <var>
• <var>: <type> - capture and convert to type
• _ - blank (skip)
• (<pattern>)*<sep> - repetition where <sep> can be any valid separator
• [<pattern>]*<sep> - repetition collected into a Vec

Supported separators are:

separator	symbol	splits at	programmable?
Space	,	whitespace (' ')	yes
Newline	;	newline ('\n' or "\r\n")	no
Paragraph	#	empty lines	no
Multispace	~	one or more whitespaces (' ')	no
Period	.	period ('.')	yes

Type Annotations

By using <var>: <type> values are automatically converted using the FromStr trait:

use simpar::parse;

parse!("42 3.14" -> count: u32, ratio: f64);
assert_eq!(count, 42);
assert_eq!(ratio, 3.14);

The program will panic, if any of the conversions fail.

Repetitions

Repeating patterns can be extracted using (<pattern>)*<separator>:

use simpar::parse;

parse!("1 2 3 4" -> (mut n: i32)*,);

assert_eq!(n.next(), Some(1));
assert_eq!(n.next(), Some(2));
assert_eq!(n.next(), Some(3));
assert_eq!(n.next(), Some(4));
assert_eq!(n.next(), None);

Repetitions return iterators, but can be directly collected into vectors using the [<pattern>]*<separator> syntax.

use simpar::parse;

parse!("1 2 3 4" -> [n: i32]*,);

assert_eq!(n, vec![1, 2, 3, 4]);

At the moment repetitions can contain at most one identifier.

Programmable separators

Some separators can be modified. {<separator> = <pattern>} sets the separator to <pattern> where <pattern> can be anything that implements the standard library Pattern trait, e.g. a string or char.

For example, if file is the content of a CSV file like

country,capital
germany,Berlin

then parsing can be done with:

parse!(file -> _; {, = ','} country, capital);

License

Simpar is distributed under the terms of both the MIT license and the Apache License (Version 2.0).