Parsing dates in online REPL

[jeromesimeon]

Using some date operations in the JavaScript version of the Ergo REPL (e.g., at https://ergorepl.netlify.com) will fail. This is due to the calendar library which uses the OCaml Str library which isn't supported by js_of_ocaml.

We should switch to the (hopefully) upcoming version of Calendar from https://github.com/ocaml-community/calendar which relies on Re.Str as soon as it is available on opam.

[jeromesimeon]

The relevant js_of_ocaml warning during compilation:

ocamlfind ocamlc -linkpkg -package js_of_ocaml.ppx -package js_of_ocaml -package calendar -package re.str -package base64 -package unix -package atdgen -I src -I extracted src/DateTime.cmo src/Monitor_t.cmo src/Monitor_j.cmo src/Util.cmo extracted/ErgoComp.cmo src/Cto_t.cmo extracted/Resources.cmo src/ErgoStdlib.cmo src/ErgoUtil.cmo src/Cto_j.cmo src/CtoImport.cmo src/LexUtil.cmo src/ErgoParser.cmo src/ErgoLexer.cmo src/ParseUtil.cmo src/ErgoConfig.cmo src/PrettyCommon.cmo src/PrettyIL.cmo src/ErgoCompile.cmo ergoc.cmo ergocJS.cmo -o ergocJS.byte
js_of_ocaml _build_js/ergocJS.byte -o _build_js/ergocJS.js
There are some missing primitives
Dummy implementations (raising 'Failure' exception) will be used if they are not available at runtime.
You can prevent the generation of dummy implementations with the commandline option '--disable genprim'
Missing primitives:
  re_search_forward

[jeromesimeon]

There is hope of a new release. Most recent thread about that is at ocaml-community/calendar#26