Implementation of surreal numbers for games There is a very nice construction by Conway of surreal numbers. They are "numbers" that contain both real numbers and ordinals, are totally ordered, and have all the properties of a field (except they do not form a set but a class).

See for instance this pdf or Wikipedia for an introduction.

They can be even more generalized to so-called "games", which are originally introduced to study combinatorial games. The original motivation of Conway was to analyze the game of Go, in particular the endgame is especially suited to be modeled with "surreal games".

My question is: do you know if anybody has implemented this approach in an AI (i.e. computer player) to improve its level at a game? I am especially interested in the case of Go, but others as well. If not, is there an obstacle or a reason why it would not be a good idea?
I don't have an answer to your question of whether the theory of Conway games has been used in building game-playing programs, but still you might be interested in the Combinatorial Game Suite, "an open-source program to aid research in combinatorial game theory" (which I first learned about here).  It includes an implementation of various standard operations on Conway games in canonical form, as well as a scripting language for describing new games.