The function dde-execute-string issues an execute transaction consisting of the string command. This string should be an appropriately formatted as described in Execute transactions. No processing of the string is performed.
On success, this function returns t. On failure, the behavior depends on the value of the errorp argument. If errorp is t (the default value), LispWorks signals an error. If it is nil, the function returns nil to indicate failure.
LispWorks User Guide and Reference Manual - 20 Sep 2017