SharePoint: How to use IF condition in InfoPath form formula?

if (BoolCondition) {
   TrueResult
}
else {
   ElseResult
}


becomes

concat(

substring(TrueResult, 1, (BoolCondition) * string-length(TrueResult)),

substring(ElseResult, 1, (not(BoolCondition)) * string-length(ElseResult)))


Source: https://blogs.msdn.microsoft.com/infopath/2006/11/27/conditional-default-values/