TODO 
   Figure out how types and widths propogate for all updated primops
   Write infer-types pass
   Remove letrec. Add to expressions: Register(input,en), ReadPort(mem,index,enable), WritePort(mem,index,enable)
   Add bit-reduce-and etc to primops
   Write pass to rename identifiers (alpha-transform)
   Update spec
      change concrete syntactical names of structural elements
      change direction names for bundle fields
      add new field for sequential or combinational
      play with non-implicit growth
      remove generics, add all combinations (adduu, addus, addss, ...)
      add assertions
      add convert to primop
      remove type from node in statement
   Future questions to address in spec:
      Introduction – motivation, and intended usage
      Philosophical justifications for all constructs
      More introduction for types, e.g. what is a ground type?
      What is a statement? What is an expression? What is a memory? Difference between vector type and memory? What are accessors for?
      Why would I ever write an empty statement? Mainly for use by compiler/passes
      What is a structural element? Duplication?
      Subtracting two unsigned numbers… Should talk to a math guy to figure it out
      What are shift left and shift right operations? HW doesn’t have these concepts. Need justification.
      What is lowered form? What is it for?



Tests:
   Error if declare anything other than module in circuit
   Error if incorrectly assign stuff, like use = instead of :=
   Error: Node not parsed for stmts