A possible workaround for supporting camlp5 on UTop

[aqjune]

Hello all,

Currently UTop directly passes an input string to UTop.parse_toplevel_phrase which in turn calls Parse.toplevel_phrase.

This implies that even if a user installs a custom preprocessor using camlp5, the input text isn't preprocessed using this.

For example, in HOL Light, a special quotation `x` means an expression called 'term' type, and its camlp5 preprocesses it as parse_term "x". However, this is not being successfully treated:

─( 11:13:52 )─< command 0 >───────────{ counter: 0 }─
utop # `1 + 2 = 3`;;
Error: Syntax error

Rather than finding a solution for fully supporting camlp5, there seems to be a quick possible workaround. If I store `1 + 2 = 3`;; as a temporary file, say tmp.ml, and load it using the #use command, this works great.

─( 13:09:39 )─< command 1 >────────────{ counter: 0 }─
utop # #use "tmp.ml";;
- : term = `1 + 2 = 3`

A downside of this solution is that UTop cannot track the history of parsed phrases, but this cost is okay to take I believe.
As a possible solution for supporting camlp5, I would like to discuss about adding this as an option to UTop.