Just out of interest (I worked on a table-driven parser for SML a couple of decades ago) - what bits of ML syntax is giving you trouble? I remember one bit that (theoretically) needed unbounded lookahead, and user-defined infix operators were fun.

There's a difficult problem with precedence and unary operators. For example:

    set_field !list_end 1 cons

cannot be parsed. Anyway since then I rewrote the lexer to work like the sibling comment and I'm still getting that working.

I am using Happy, which is a yacc-alike for Haskell. I found it mostly straightforward (however, I use the OCaml/Haskell/F# style of lexically distinguishing infix operators from variable names).