method OptionAbstract.prototype.fmimport { OptionAbstract } from "https://deno.land/x/careful@v0.1.0/mod.ts"; fm<NT>(cb: (v: T) => OptionAbstract<NT>): OptionAbstract<T> | OptionAbstract<NT>Type ParametersNTParameterscb: (v: T) => OptionAbstract<NT>ReturnsOptionAbstract<T> | OptionAbstract<NT>