How to Parse Nested Strings: Recursive Descent vs. Top-Down Parsing?

Creating a Parser: Exploring Recursive and Top-Down Approaches

Understanding how to create a parser can be challenging, especially when working with complex input strings. To build a parser capable of parsing a nested string like "{key1 = value1 | key2 = {key3 = value3} | key4 = {key5 = { key6 = value6 }}}" and outputting a nested map, consider these approaches:

Recursive Descent Parsing

This technique involves breaking the input string into smaller pieces and applying the parsing algorithm recursively on these pieces. By analyzing the input's grammatical structure, you can create rules to match each component and extract the desired data. For example, start by defining a rule for the outermost curly braces {}, followed by rules for key-value pairs and nested objects.

Top-Down Parsing (LL Parsing)

With this approach, you begin by examining the first token in the input string and constructing a parse tree that represents the grammatical structure of the input. Based on the tree's current position, the parser predicts the next token and checks if it matches the actual token in the input. If the prediction is incorrect, the tree is revised, and the parsing process continues.

Implementation Recommendations

To write a parser in Go, consider referencing the parser code in the standard library at "http://golang.org/src/pkg/go/parser/parser.go". You can also consult resources like:

• Rob Pike's talk on lexing in Go: "http://www.youtube.com/watch?v=HxaD_trXwRE"
• Introduction to recursive descent parsing: "http://www.cs.binghamton.edu/~zdu/parsdemo/recintro.html"
• Top-down parsing resources: "http://javascript.crockford.com/tdop/tdop.html", "http://effbot.org/zone/simple-top-down-parsing.htm"

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