Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Syntax proposal: let punning #10013

Merged
merged 3 commits into from Dec 8, 2020
Merged

Syntax proposal: let punning #10013

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
d65593b
Let-punning: allow "let* x" syntax without an explicit binding.
stedolan Nov 10, 2020
a5ace5c
Support let-punning in let%foo extensions
stedolan Dec 1, 2020
382850e
changes
stedolan Dec 1, 2020
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Jump to
Jump to file
Failed to load files.
Diff view
Diff view
5 changes: 5 additions & 0 deletions Changes
View file
Open in desktop
Expand Up @@ -3,6 +3,11 @@ Working version

### Language features:

- #10013: Let-punning
Allow 'let* x in ...' and 'let%ext x in ...' as shorthand for
'let* x = x in ...' and 'let%ext x = x in ...' respectively.
(Stephen Dolan, review by Gabriel Scherer)

### Runtime system:

### Code generation and optimizations:
Expand Down
9,733 changes: 4,909 additions & 4,824 deletions boot/menhir/parser.ml
View file
Open in desktop

Large diffs are not rendered by default.

31 changes: 22 additions & 9 deletions parsing/parser.mly
View file
Open in desktop
Expand Up @@ -458,6 +458,7 @@ let extra_rhs_core_type ct ~pos =
type let_binding =
{ lb_pattern: pattern;
lb_expression: expression;
lb_is_pun: bool;
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I we are going to have this wart in the codebase, let's turn it into a strength that will make ocamlformat people happy: use it also for binding operators, and use this boolean when reprinting the AST.

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I'm not quite sure what you're suggesting here? The type let_binding is not part of the AST, but rather a temporary structure used by parser.mly to share code between various constructs that have similar syntax.

lb_attributes: attributes;
lb_docs: docs Lazy.t;
lb_text: text Lazy.t;
Expand All @@ -469,27 +470,30 @@ type let_bindings =
lbs_extension: string Asttypes.loc option;
lbs_loc: Location.t }

let mklb first ~loc (p, e) attrs =
let mklb first ~loc (p, e, is_pun) attrs =
{
lb_pattern = p;
lb_expression = e;
lb_is_pun = is_pun;
lb_attributes = attrs;
lb_docs = symbol_docs_lazy loc;
lb_text = (if first then empty_text_lazy
else symbol_text_lazy (fst loc));
lb_loc = make_loc loc;
}

let addlb lbs lb =
if lb.lb_is_pun && lbs.lbs_extension = None then syntax_error ();
{ lbs with lbs_bindings = lb :: lbs.lbs_bindings }
gasche marked this conversation as resolved.
Show resolved Hide resolved

let mklbs ~loc ext rf lb =
{
lbs_bindings = [lb];
let lbs = {
lbs_bindings = [];
lbs_rec = rf;
lbs_extension = ext ;
lbs_loc = make_loc loc;
}

let addlb lbs lb =
{ lbs with lbs_bindings = lb :: lbs.lbs_bindings }
} in
addlb lbs lb

let val_of_let_bindings ~loc lbs =
let bindings =
Expand Down Expand Up @@ -2418,7 +2422,7 @@ labeled_simple_expr:
%inline let_ident:
val_ident { mkpatvar ~loc:$sloc $1 }
;
let_binding_body:
let_binding_body_no_punning:
let_ident strict_binding
{ ($1, $2) }
| let_ident type_constraint EQUAL seq_expr
Expand Down Expand Up @@ -2454,6 +2458,12 @@ let_binding_body:
{ let loc = ($startpos($1), $endpos($3)) in
(ghpat ~loc (Ppat_constraint($1, $3)), $5) }
;
let_binding_body:
| let_binding_body_no_punning
{ let p,e = $1 in (p,e,false) }
| val_ident %prec below_HASH
{ (mkpatvar ~loc:$loc $1, mkexpvar ~loc:$loc $1, true) }
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Nitpick: I suspect that if you had used a punned_binding rule for this case, you could have shared it with the letop_binding_body grammar. (The %prec annotation would stay here, I guess?)

;
(* The formal parameter EXT can be instantiated with ext or no_ext
so as to indicate whether an extension is allowed or disallowed. *)
let_bindings(EXT):
Expand Down Expand Up @@ -2485,6 +2495,9 @@ and_let_binding:
letop_binding_body:
pat = let_ident exp = strict_binding
{ (pat, exp) }
| val_ident
(* Let-punning *)
{ (mkpatvar ~loc:$loc $1, mkexpvar ~loc:$loc $1) }
| pat = simple_pattern COLON typ = core_type EQUAL exp = seq_expr
{ let loc = ($startpos(pat), $endpos(typ)) in
(ghpat ~loc (Ppat_constraint(pat, typ)), exp) }
Expand All @@ -2495,7 +2508,7 @@ letop_bindings:
body = letop_binding_body
{ let let_pat, let_exp = body in
let_pat, let_exp, [] }
| bindings = letop_bindings pbop_op = mkrhs(ANDOP) body = let_binding_body
| bindings = letop_bindings pbop_op = mkrhs(ANDOP) body = letop_binding_body
{ let let_pat, let_exp, rev_ands = bindings in
let pbop_pat, pbop_exp = body in
let pbop_loc = make_loc $sloc in
Expand Down
10 changes: 8 additions & 2 deletions parsing/pprintast.ml
View file
Open in desktop
Expand Up @@ -1314,8 +1314,14 @@ and bindings ctxt f (rf,l) =
(list ~sep:"@," (binding "and" Nonrecursive)) xs

and binding_op ctxt f x =
pp f "@[<2>%s %a@;=@;%a@]"
x.pbop_op.txt (pattern ctxt) x.pbop_pat (expression ctxt) x.pbop_exp
match x.pbop_pat, x.pbop_exp with
| {ppat_desc = Ppat_var { txt=pvar; _ }; ppat_attributes = []; _},
{pexp_desc = Pexp_ident { txt=Lident evar; _}; pexp_attributes = []; _}
when pvar = evar ->
pp f "@[<2>%s %s@]" x.pbop_op.txt evar
| pat, exp ->
pp f "@[<2>%s %a@;=@;%a@]"
x.pbop_op.txt (pattern ctxt) pat (expression ctxt) exp
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Remark: if I understand correctly, we have pretty-printing support for the binding operator form, but not for the extension form. This is just fine as far as I am concerned.


and structure_item ctxt f x =
match x.pstr_desc with
Expand Down
11 changes: 11 additions & 0 deletions testsuite/tests/parsetree/source.ml
View file
Open in desktop
Expand Up @@ -7414,3 +7414,14 @@ let test = function

let test = function
| (`A | `B) as x | `C -> ()

(* Let-punning *)
module M = struct
let (let*) x f = f x
let (and*) a b = (a, b)
let x = 1 and y = 2 and z = 3
let p =
let* x and* y and* z in (x,y,z)
let q =
let%foo x and y and z in (x,y,z)
end