Convert call dll from Metastock to MetaTrader4

Please help me to call dll file using MT4

File name: FileName.dll
Function name is : CheckFunction

Metastock formula to call dll function is :
Buy
ExtFml( "FileName.CheckFunction") = 1

Sell
ExtFml( "FileName.CheckFunction") = 0

Convert call dll from Metastock to MetaTrader4