Gambit Parser

A rust parser for gambit extensive form game (.efg) files.

Usage

use gambit_parser::ExtensiveFormGame;
use std::fs::File;
use std::io::Read;

let mut buffer = String::new();
File::open("my path")?.read_to_string(&mut buffer)?;
let parsed: ExtensiveFormGame<'_> = buffer.as_str().try_into()?;

A parsed game serializes back to the .efg format via Display:

use gambit_parser::WriteMode;

// `to_string()` (plain `Display`) reproduces the input faithfully
let text = parsed.to_string();
// or pick how much of each shared infoset/outcome to repeat
let compact = parsed.display(WriteMode::Minimal).to_string();
let expanded = parsed.display(WriteMode::Exhaustive).to_string();

Remarks

Gambit's reader duplicates runs of backslashes when reading a quoted label; this parser does not reproduce that bug.

Chance-node probabilities are kept as written and are not required to sum to one, matching Gambit (which performs no such check). A file that approximates a distribution with rounded decimals — e.g. 0.333333 repeated three times, summing to 0.999999 — parses fine; normalize the probabilities yourself if you need an exact distribution.

This parser diverges from Gambit's self-delimiting lexer in a few ways that only affect hand-written files; everything Gambit's own writer emits round-trips. It requires whitespace between tokens, so "x"1, t"" 1, and an empty { } player list are rejected where Gambit accepts them, and it rejects trailing content after the root subtree that Gambit ignores. Conversely, it compares repeated outcome and probability definitions numerically rather than textually, so { 1/2, 2 } followed by { 0.5, 2 } for the same id parses here but errors in Gambit.

To Do

Parsing and serialization are implemented, but the parsed ExtensiveFormGame borrows the underlying file bytes and is read-only. A full data model would need an owned version of ExtensiveFormGame that can be constructed and modified in memory rather than only parsed from text; that's not implemented yet.