Absyn will parse the expression `let x = e1 in e2` into
APP(APP(IDENT "LET", LAM(VIDENT "x", IDENT "e2")), IDENT "e1")
The record syntax `rec.fld1` is converted into something of
the form
APP(IDENT "....fld1", IDENT "rec")
where the dots will actually be equal to the value of
GrammarSpecials.recsel_special (a string).