chinna1986 / spire-nodeset-example

An example of parsing a simple language in Java using JFlex and CUP

Node Set Java parsing example

This is an excerpt from Spire – Spotify Internal Remote Execution, a server orchestration tool. It serves as an example of doing text parsing of a small language in Java. For completeness, it also includes a small driver program to test the language.

Source organization

This is a standard Maven project. Compiling should be as easy as

mvn compile

or

./nodeset

The nodeset script runs compilation if target/classes is missing, and will then run the NodeSetMain class. (Yes, this was developed on a *nix system!)

The CUP grammar file is in src/main/cup, and the scanner is in src/main/jflex. Some glue classes are in the java subdirectory.

Language

The language is a simple set-based language. It supports the four basic operators, set literals, singleton sets and function calls.

Basic operators

• a | b or a ∪ b
• a & b or a ∩ b
• a \ b or a / b
• a ^ b or a ⊖ b or a ∆ b

Set literals

• ∅
• [ "a", "b", "c" ]

Singleton sets

• @a.b.c

is equivalent to

• [ "a.b.c" ]

and is convenient when working with hostnames.

Function calls

• a or a()
• a("b", 42, 4711, @a.b.c)

Examples

As this usually works with Spotify's internal host databases, this contains an example function call handler called FileSystemContext. This implements two functions:

• fs.ls("path") to return a set of file names, and
• fs.ls.current equivalent to fs.ls("."), but showing a function call without parentheses.

This allows you to run the nodeset program with expressions like

• nodeset ∅
• nodeset @example.com
• nodeset '["example.com"]'
• nodeset 'fs.ls("/") & fs.ls("/mnt")'

These examples are executed if you run ./nodeset without arguments.

Caveats

Error reporting is very crude, and there is essentially nothing aside from CUP's standard stuff here.

Authors

Tommie Gannert