Record 'zooming'

--Works, but verbose:

let lineParser' = do
      [email protected]{[email protected]{
        [email protected]{sourceLine, sourceColumn}}} <- getParserState
      let pstateSourcePos' :: MP.SourcePos
          pstateSourcePos' = pstateSourcePos{sourceLine = mkPos lineNo, sourceColumn = mkPos 1}
      setParserState parserState{statePosState=statePosState{pstateSourcePos=pstateSourcePos'}}
      lineParser
      
-- I want to do this instead because it's less verbose, but it doesn't compile:
let lineParser' = do
      [email protected]{[email protected]{
        [email protected]{sourceLine, sourceColumn}}} <- getParserState
      let pstateSourcePos' :: MP.SourcePos
          pstateSourcePos' = pstateSourcePos{sourceLine = mkPos lineNo, sourceColumn = mkPos 1}
      setParserState parserState{statePosState=statePosState{pstateSourcePos=pstateSourcePos'}}
      lineParser