Fast Report's expression parser does not support nested expressions in the way you are trying to use them. As you only have the bundled Embarcadero version of Fast Reports, your only solution is to modify the memo view directly in your Delphi code or create a calculated field for the memoview component.
The paid for version of Fast Reports (Standard and up) support event handlers and scripting at the report component level, so if you wanted to keep the display logic in your report, then you could use scripting and use the OnBeforePrint
event of the MemoView in question within the Fast Reports designer.