Every bot needs some poker-specific logic to decide how to act. OpenHoldem provides a basic scripting-language for that, which was inherited from WinHoldem. The logic is action-centered, i.e. everytime it is your turn the following basic questions have to be answered:

• “shall I go allin?” — f$allin (boolean, interpreting 0 as false and everything else as true)

• “shall I click a betpot-button?” – f$betpot_2_1...f$betpot_1_4 for twice betpot to 1/4 betpot.

• “shall I raise, and how much?” — f$betsize

• “shall I (min-)raise” — f$raise (mainly for Fixed Limit; boolean)

• “shall I call” — f$call (boolean)

• “shall I check” — f$check (boolean)

• “shall I fold” — f$fold (boolean)

Per default f$check evaluates to true if it is free to call and f$fold is always true, so if all questions were answered with 0 or false, your hand-will be check-folded.

OH-script uses C(++)-style mathematical expressions, i.e. the same mathematical operators like the C-programming-language and OpenHoldems built-in symbols. An example:

##f$sitout##
0                                // 0=off 1=on  
&& issittingin                   // i am sitting in  
&& (betround==2 || betround==3)  // it is the flop or turn  
&& nopponentsdealt<=5            // 5 or less opponents 

Every bot needs such a formula file, even if it is programmed in C++. There are no standalone C++-bots; the user-DLL is just a programming extensions that make it possible to extend the functionality of OpenHoldem by providing additional symbols (constants and parameter-less functions). The very minimum is a small OH-script or OpenPPL formula that redirects every primary function to a DLL-function.

##notes##
// Very small OH-formula, that redirects 
// primary functions to C++-functions in the user.DLL.

##f$alli##
dll$alli

##f$betsize##
dll$betsize

##f$raise##
dll$rais

##f$call##
dll$call

In practice formulas can become arbitary complex, but those are the basic principles you will need to understand. We will deal with the details of bot-programming in the chapter about OH-script.

The OpenHoldem scripting language will detect various error conditions for you and warn you of these conditions. Each time a formula is loaded, it is “parsed” for correctness – if there are any syntactical errors upon this parse, then a message box will be displayed that alerts you to the location of this error.

Additionally, several classes of run-time errors will be detected, including divide-by-zero and infinite recursion. Note that the OH-Script language does not support recursion in any form, due to the absence of the assignment operator and function parameters to control the recursion depth.

All OH-script-bots are self-contained. Once all questions f$alli .. f$fold have been answered the best action is well-defined. Therefore OH-script does not support a default-bot. “All power (and responsibilities) to the user” is the motto of OH-script. Things are slightly different for OpenPPL, the other programming language, however. An OpenPPL-bot might be “incomplete”. The end of a code-section might be reached without a matching action being found, then the default.bot will take over. We will talk about OpenPPL and this default-bot in the next chapters briefly; all the details are in an extra handbook, the OpenPPL-manual.