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exercism fetch fsharp sgf-parsing

Sgf Parsing

Parsing a Smart Game Format string.

SGF is a standard format for storing board game files, in particular go.

SGF is a fairly simple format. An SGF file usually contains a single tree of nodes where each node is a property list. The property list contains key value pairs, each key can only occur once but may have multiple values.

An SGF file may look like this:

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(;FF[4]C[root]SZ[19];B[aa];W[ab])

This is a tree with three nodes:

As you can imagine an SGF file contains a lot of nodes with a single child, which is why there's a shorthand for it.

SGF can encode variations of play. Go players do a lot of backtracking in their reviews (let's try this, doesn't work, let's try that) and SGF supports variations of play sequences. For example:

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(;FF[4](;B[aa];W[ab])(;B[dd];W[ee]))

Here the root node has two variations. The first (which by convention indicates what's actually played) is where black plays on 1-1. Black was sent this file by his teacher who pointed out a more sensible play in the second child of the root node: B[dd] (4-4 point, a very standard opening to take the corner).

A key can have multiple values associated with it. For example:

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(;FF[4];AB[aa][ab][ba])

Here AB (add black) is used to add three black stones to the board.

There are a few more complexities to SGF (and parsing in general), which you can mostly ignore. You should assume that the input is encoded in UTF-8, the tests won't contain a charset property, so don't worry about that. Furthermore you may assume that all newlines are unix style (\n, no \r or \r\n will be in the tests) and that no optional whitespace between properties, nodes, etc will be in the tests.

The exercise will have you parse an SGF string and return a tree structure of properties. You do not need to encode knowledge about the data types of properties, just use the rules for the text type everywhere.

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.