Support string-typed parameters

[rainoftime]

I notice that we can set boolean or integer typed parameters to a tactic such as `simplify'. Can we specify a parameter whose type is string? Thank you!

          "simplify": 
                "boolean": [
                    "elim_and",
                    "som",
                    "blast_distinct",
                    "flat",
                    "hi_div0",
                    "local_ctx",
                    "hoist_mul"
                ]
            },

[mbalunovic]

Hi, unfortunately we do not support string parameters at the moment.