Functional Programming with Phunkie: Building a PHP JSON Parser

This two-part tutorial demonstrates building parser combinators in PHP using the Phunkie functional library. Marcello Duarte, the library's creator, guides you through the process.

This tutorial builds upon basic parser concepts, progressing to more advanced sequencing and choice strategies.

Sequencing Combinators

A sat (satisfies) parser is introduced, checking if a character meets a given predicate. It leverages the item, result, and zero primitive parsers. Building on sat, simple parsers like char, digit, lower, and upper are easily created.

Choice Combinators

Real-world grammars require handling choices. The plus combinator allows choosing between two parsers. This is implemented as an or method within the Parser class for improved syntax. letter (lowercase or uppercase) and alphanum (letter or digit) parsers exemplify this.

Recursive Combinators

Recursive combinators enable non-deterministic parsing. A word parser demonstrates this, recursively matching sequences of letters. A string parser recognizes a specific string within a larger input. Recursion is handled carefully to avoid stack overflows.

Simple Repetitions

The many parser generalizes repetition, allowing for zero or more occurrences of a parser. many1 is introduced for at least one occurrence. A nat (natural number) parser and an int parser are built using many1 and demonstrate casting parsed results to integers.

Repetition with Separators

The sepBy1 combinator handles repetitions separated by another parser. This is used to create an ints parser for parsing lists of integers in the style of PHP arrays (e.g., [1,-42,500]). A surrounded helper function further refactors this.

A JSON Parser

A JSON parser is constructed using the previously defined combinators. The json_value parser acts as a top-level choice parser, combining other specialized parsers (e.g., json_string, json_boolean, json_number, json_array, json_object). The sepBy1array combinator is used to build arrays, and immutable maps are used for JSON objects.

The tutorial concludes with links to the Phunkie repository and the author's parser combinator repository. The author encourages questions and comments on Twitter.

[1] – Phunkie repository: https://www.php.cn/link/630d790d0716246ca1aa250a6f86f755 [2] – Marcello Duarte’s parsers combinators repository: https://www.php.cn/link/793aaa24e931c05d077f434e33485574

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