==========================================================================
I. MAIN CHANGES MADE TO FLINT VERSION 1.1

02/02/1998 
  Merged Version 1.1 with SML/Nj 110.0.3 to create 1.1+
 
02/04/1998
  Changed FLINT IL and LTYKERNEL in the following way:

     flint/flintil.sig
     flint/flintil.sml
       New fkind, no more return result type for fundec
       no more type bindings in tfundec.

     flint/ltykernel.sig
     flint/ltykernel.sml
       TK_TYC and TK_TBX now renamed as TK_MONO and TK_BOX
       new raw field to indicate if a TC_ARROW is cooked or raw
       LT_FCT now takes  multiple arguments as well.

  Reorganize the files a little bit, and propagate all of the
  above changes to the other files.

02/05/1998
  Directory reorganizations

02/06/1998
  To eliminate references to LtyEnv from transmodules.sml
  To eliminate references to LtyKernel from translate.sml
  To eliminate references to LtyEnv from translate.sml
  Then to reformat PLambdaType to support exactly what is 
  required by the trans and mcomp directories.

==========================================================================
II. IMPLEMENTATION NOTES: 

flint.sig
flint.sml

   * fkind could be a list of attributes
   * rkind --- tyc is only used empty vector, we could introduce
               a new construct called RK_VECTOR0 of tyc ? 
               then the tyc can go away.
   * RK_RECORD could contain a list of labels, however, we could add
     it later, it should not impact the rest of the code much
   * type dcon --- conrep should go away once we have the full 
       type information about datatypes
   * funtions will be divided into two categories: raw vs. cooked
       raw refers to those whose calling conventions have been fixed.
       cooked means those whose calling conventions are being determined;
       most likely, they depend on what kind of argument and result types
       they have.
   * EXNC and EXNF should be merged, we should only provide one construct,
     that is, the etag primop which takes a string or string ref and 
     returns a 'a etag value. Non-value carrying exceptions are considered 
     as exceptions that carry unit value. Similarly, CON and SWITCH on 
     exceptions should be replaced by Harper & Stone's "tag" and "iftagof"
     construct. 

ltykernel.sig
ltykernel.sml

   * LT_PST is used for avoiding writing down huge type information
     for imported modules; we can get rid of this if we change the
     the list of import ids into a list of import access paths.
   * TC_NVAR and TC_ABS are not used for the time being
   * TC_CONT and LT_CNT are used for the cps/convert.sml only; the 
     source-level cont type is denoted as a TC_PRIM tyc.
   * TC_BOX should become a primtiive tyc if wrap and unwrap become
     primitive operators. 
   * TC_SUM and TC_FIX require clean-up. Do we need to distinguish
     between enumeration types and other arbitrary datatypes ? 

flinttype.sig
  
   * Get rid of tcc_unit as it ought to be just RECORD []. 



==========================================================================
III. PAST NOTES:

  FILES CHANGED TO MIGRATE TO THE NEW FLINT

    a. main working directories: new and nopt
       convert.sml and switch.sml are now in the nopt directories also.
    b. directories such type and opt and cps/conv will become
       obsolete in the future.

  FILES CHANGED TO SUPPORT NEW FORM of SWITCH statement in PLambda

    mcomp/matchcomp.sml
    opt/normalize.sml
    plambda/chkplexp.sml
    plambda/plambda.sig
    plambda/plambda.sml  
    plambda/pplexp.sml
    trans/literals.sml
    trans/pequal.sml
==========================================================================
THE TRANSLATION PHASE

    NOW:  SML Absyn --> Lambda --> CPS
 FUTURE:  SML Absyn --> FLINT --> CPS (FLINT)

The current structure:

	SML Absyn   
	--> PLambda (match compilation)           ----
	--> FLINT   (a-normalize, multiple arg)      | alt. route
	--> Lambda  (non-opt, single arg again)   <---
	--> Lambda  (opt)
	--> Lambda  (rep-analysis, inlining type primitives)
	--> Lambda  (narrowed, tfn and tapp become fn and app)
	--> Lambda  (lambdaopt and reorder)
     *  --> CPS     (switch optimized)
     *	--> CPS     (cps transed with wrapper eliminated)
     *  --> CPS     (cpsopt)
     *  --> CLO     (closure)
     *  --> MLRISC  


 Directory structure:     

        trans    (* Absyn -> PLambda, calls mcomp *)
        mcomp    (* match compilation *)
        plambda  (* refer to plambdatype *)
	
        flint    (* refer to flinttype ? *)
	
        lambda   (* refer to lambdatype *)
        opt      (* lambda optimizations *)
        reps     (* representation analysis *)
	
        narrow   (* refer to narrowtype *)
        obsol    (* files that are already obsolete *)

The future structure:

	SML Absyn   
	--> PLambda                               
	--> FLINT   (a-normalize, multiple arg, + switch opt + exn elim?)  
        --> FLINT   (flint opt, reorder, lambdaopt, cpsopt)
        --> FLINT   (post-rep-analysis ?)
        --> CPS     (cps convert, cont-related primop made explicit)
        --> CLO     (closure convert, fundec flattening)
        --> MLRISC  

To do:  changing the datatype representations in the front-end elaborator
        propagating datatypes from the frontend into FLINT
        update the FLINT typechecker to support strong typing
        propagating the labels of records and sums into FLINT as well

=========================================================================
PHASE I   SML Absyn --> PLambda

     4-FLINT/plambda/plambda.sig
     4-FLINT/plambda/plambda.sml
     4-FLINT/plambda/pplexp.sml
     4-FLINT/plambda/chkplexp.sml   
     
     4-FLINT/mcomp/matchcomp.sml
     4-FLINT/mcomp/mccommon.sml
     4-FLINT/mcomp/tempexpn.sml

     4-FLINT/trans/translate.sml
     4-FLINT/trans/transmodules.sml
     4-FLINT/trans/transtypes.sml
     
     4-FLINT/trans/pequal.sml
     4-FLINT/trans/interp.sml
     4-FLINT/trans/literals.sml

Needs an interface of FLINT types used 
by this translation.

=========================================================================
PHASE II  PLambda --> FLINT

     4-FLINT/flint/flintnm.sml

Currently does two things: 
  (1) A-normalization
  (2) argument expansions

Notice there should not be any translation on 
lambda types. PLambda ought to carry normalized
types (i.e., known cooked types should be raw)

Will do more in the future, potentially:
  (1) Not treating exceptions as constructors
  (2) Elimination of exception switches ?
  (3) Effect inference ?

=========================================================================
PHASE III FLINT --> FLINT 


     4-FLINT/flint/flint.sig
     4-FLINT/flint/flint.sml
     
     4-FLINT/flint/debindex.sml
     4-FLINT/flint/ltykernel.sig
     4-FLINT/flint/ltykernel.sml

---------------------------------------------------

     4-FLINT/flint/lambdatype.sig
     4-FLINT/flint/lambdatype.sml
     4-FLINT/flint/ltyenv.sig
     4-FLINT/flint/ltyenv.sml
     
     4-FLINT/flint/ltysingle.sig
     4-FLINT/flint/ltysingle.sml
     
     4-FLINT/flint/ppflint.sig
     4-FLINT/flint/ppflint.sml
     (* 4-FLINT/flint/chkflint.sml *)
     4-FLINT/flint/flintutil.sml

=========================================================================
PHASE IV  FLINT --> Lambda

     4-FLINT/flint/flint2lambda.sml

Goes from multiple arguments back
into singleton argument.


=========================================================================
PHASE V   PLambda -> Lambda

     4-FLINT/opt/normalize.sml
  
Alternative route: goes from PLambda directly 
into Lambda.

=========================================================================
PHASE VI  Lambda -> Lambda

     4-FLINT/lambda/checklty.sml
     4-FLINT/lambda/lambda.sig
     4-FLINT/lambda/lambda.sml
     4-FLINT/lambda/lambdavar.sig
     4-FLINT/lambda/lambdavar.sml
     4-FLINT/lambda/lexputil.sml
     4-FLINT/lambda/mcprint.sml
     
     4-FLINT/opt/flintcomp.sml
     4-FLINT/opt/specialize.sml
     4-FLINT/opt/equal.sml
     4-FLINT/opt/lcontract.sml
     4-FLINT/opt/coerce.sml
     4-FLINT/opt/wrapping.sml
     4-FLINT/opt/ltyprim.sml
     4-FLINT/opt/ltycomp.sml
     4-FLINT/opt/ltnarrow.sml
     4-FLINT/opt/lambdaopt.sml
     4-FLINT/opt/reorder.sml

=========================================================================
PHASE VII Lambda -> CPS

     5-CPS/conv/convert.sml
     5-CPS/conv/cpstrans.sml
     5-CPS/conv/switch.sml

=========================================================================
PHASE VIII CPS -> CPS

The cpsopt and closure phase should be rewritten
to be performed upon FLINT instead.

=========================================================================

There are four clients of the Lambda Types:

(1) PLambda  --- used by translate --- plambdatype.sig plambdatype.sml
(2) FlintType --- used by flint clients --- flinttype.sig flinttype.sml
(3) Lambda --- used by the old Lambda --- lambdatype.sig lambdatype.sml
(4) CPS --- narrowtype.sig and narrowtype.sml

=========================================================================
Goal: make the FLINT backend independent of the front end

Right now, the front-end references the following structures:
  LtyKernel, LambdaType, Lambda, LambdaVar, 
  DebIndex, PrimTyc, PrimOp.

The FLINT phase references the following structures in the front 
end:
  Access --- the conrep for datatypes
  Symbol --- names of constructors and record labels
  ErrorMsg --- for debugging only

LtyKernel

   3-Semant/pickle/pickmod.sml
   3-Semant/pickle/unpickmod.sml
      (* must use LtyKernel for pickling and unpickling *)

   5-CPS/conv/convert.sml
   5-CPS/opt/contract.sml
   5-CPS/opt/flatten.sml
   5-CPS/opt/uncurry.sml
      (* currently uses both LtyKernel and NarrowType; LtyKernel is
         used for pattern-matching to support unboxed float vectors *)

LambdaType

   3-Semant/pickle/unpickmod.sml 
      (* currently use LambdaType, but really it should use something
         that is more basic than LambdaType *)

Lambda

   1-TopLevel/*/*.sml (* currently Lambda is used for inlining *)
   3-Semant/basics/inlinfo.sml       (* Lambda used for inlining *)
   3-Semant/pickle/pickmod.sml       (* pickled for cross-mod-inl *)
   3-Semant/pickle/unpickmod.sml     (* pickled for cross-mod-inl *)
   5-CPS/conv/convert.sml            (* translation into CPS *)
   5-CPS/conv/switch.sml             (* translation into CPS *)
   5-CPS/cps/cpscomp.sml             (* translation into CPS *)
   5-CPS/cps/cpsphases.sig           (* translation into CPS *)

   We should replace Lambda.lexp with FLINT.prog (?); eventually
   Lambda should go away.

LambdaVar

   1-TopLevel/interact/compile.sml    (* used in compInfo *)
   3-Semant/elaborate/elabutil.sml    (* type of compInfo *)
   3-Semant/basics/access.sig         (* used in access path *)
   3-Semant/basics/access.sml         (* used in access path *)
   3-Semant/pickle/pickmod.sml        (* pickling of access *)
   3-Semant/pickle/unpickmod.sml      (* pickling of access *)
  
   otherwise, it is heavily used by 4-FLINT and 5-CPS

DebIndex

   3-Semant/elaborate/elabmod.sml   (* we track depth during elaboration *)
   3-Semant/elaborate/elabutil.sig  (* used by context type *)
   3-Semant/elaborate/elabutil.sml  (* used by context type *)
   3-Semant/modules/evalent.sml     (* we track depth during elaboration *)
   3-Semant/modules/instantiate.sml (* we track depth during elaboration *)
   3-Semant/modules/modules.sig     (* for lty memoization *)
   3-Semant/modules/modules.sml     (* for lty memoization *)
   3-Semant/modules/sigmatch.sml    (* we track depth during elaboration *)

   3-Semant/pickle/pickmod.sml    (* pickling of IL *)
   3-Semant/pickle/unpickmod.sml  (* unpickling of IL *)
   3-Semant/types/types.sig       (* used by LBOUND tv to ease translation *)
   3-Semant/types/types.sml       (* also by memoization on large types *)
   3-Semant/types/typesutil.sig   (* used by reformat, soon obsolete *)

PrimTyc

   3-Semant/pickle/pickmod.sml    (* pickling of types *)
   3-Semant/pickle/unpickmod.sml  (* unpickling of types *)
   3-Semant/types/basictypes.sml  (* PRIMITIVE info, initial environment *)
   3-Semant/types/types.sig       (* PRIMITIVE info *)
   3-Semant/types/types.sml       (* PRIMITIVE info *)
   3-Semant/types/typesutil.sml   (* the use of PrimTyc.ptc_void *)
   5-CPS/cps/cps.sml              (* used by translation from lty to cty *)

PrimOp

   3-Semant/basics/inlinfo.sml    (* inlining information *)
   3-Semant/statenv/prim.sml      (* initial environment *)
   3-Semant/pickle/pickmod.sml    (* pickling of inlinfo and IL *)
   3-Semant/pickle/unpickmod.sml  (* unpickling of inlinfo and IL *)
   5-CPS/conv/convert.sml         (* translation to CPS primops *)
   9-Misc/profile/sprof.sml       (* instrumenting absyn *)
   9-Misc/profile/tprof.sml       (* instrumenting absyn *)

=========================================================================