Make possible the parsing of the counting example of *Clock-directed Modular Code Generation for Synchronous Data-flow Languages* (https://www.di.ens.fr/~pouzet/bib/lctes08a.pdf).
```
-- count the number of top between two tick
node counting (tick:bool; top:bool)
returns (o: int)
var v: int;
let o = if tick then v else 0 -> pre o + v;
v = if top then 1 else 0;
tel;
```
The one-line comment rule was inspired from https://mukulrathi.com/create-your-own-programming-language/parsing-ocamllex-menhir/. Note their typo using `single_line_comment` instead of `read_single_line_comment`.
Otherwise for the following code:
```
node test (i: real) returns (o: real);
let
o = 0.0;
tel
```
was experiencing:
```
Fatal error: exception Stdlib.Parsing.Parse_error
Raised at Stdlib__Parsing.yyparse.loop in file "parsing.ml", line 139, characters 8-25
Called from Stdlib__Parsing.yyparse in file "parsing.ml", line 165, characters 4-28
Re-raised at Stdlib__Parsing.yyparse in file "parsing.ml", line 184, characters 8-17
Called from Parser.main in file "parser.ml" (inlined), line 1110, characters 4-44
Called from Main in file "main.ml", line 70, characters 16-68
```
Note that `%token REAL` doesn't help to solve this error, but it doesn't seem to be any reason for not having it.
