A novel method for the incremental parallelisation of Fortran-77 codes is described. This method is used to construct an interactive compiler which compiles by means of a succession of source-to-source transformations. The key to the compiler is its potentially extensible transformation engine, which gradually introduces parallelism into the code, with each transformation producing a runnable, correct version of the program. The compiler is described from strategy through to implementation, including a discussion on how the compiler uses laziness to ensure that the user is not asked repetitive or unnecessary questions. Results are presented that demonstrate the viability of this unusual approach.