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matchertext

Description

matchertext is a "syntactic discipline" that allows for cross-language embedding of source code. It was invented by Bryan Ford (who also invented parsing expression grammars and packrat parsing). To learn more, see Ford's introductory blog post, and his more substantial paper. Briefly (quote from the blog post),

The pragmatic essence of the matchertext idea is simple. First, we define six
particular ASCII characters as matchers: namely the open and close parentheses
(), the square brackets [], and the curly braces {}. We call these characters
matchers because their traditional, already-ubiquitous purpose is to be used in
matching pairs to surround and delimit other text.

Now we define matchertext as any plain text string conforming to one additional
rule or “syntactic discipline”: namely that matchers must match, throughout any
matchertext string, without exception. Nesting is allowed, but must use
corresponding matchers. For example, the string ‘([{foo}])’ is valid
matchertext, but strings like ‘(foo’, ‘bar}’, or ‘(]’ are not matchertext.

The matchertext egg extends the Scheme language to be able to host matchertext in string literals.

Syntax

The syntax for matchertext string literals is as follows.

literal     <-  '#M' nested '"(' mtxt ')"'
nested      <-  '(' nested ')' | '[' nested ']' | '{' nested '}' | ε
mtxt        <-  non-matcher mtxt | '(' mtxt ')' mtxt | '[' mtxt ']' mtxt | '{' mtxt '}' mtxt | ε
non-matcher <-  any character except one of ()[]{}

In the simplest case, nested matches the empty string in literal. Then, the literal is equivalent to a string with contents mtxt. When nested matches a non-empty sequence of openers followed by closers:

nested ::= openers closers

then any string enclosed in openers and closers inside mtxt is interpreted as an Scheme expression that evaluates to a string. This is to allow for interpolation.

Examples

To run the examples, don't forget to

(import matchertext)

Simple usage

(string=? "Hello, world!" #M"(Hello, world!)") ; #t

(string=? "\\([{}])" #M"(\([{{}]))"); #t

(define greeting "Hello")
(string=? "Hello, world!" #M{}"({greeting}, world)") ; #t

Author

Hernán Ibarra Mejia

Repository

Development happens in SourceHut.

Requirements

None (but testing requires the test egg).

Version history

2.0

Port to C6, change to standard syntax, and add support for interpolation.

1.0

Initial release.

License

GPLv3.