Simplified tspatternmatching, updated from simplified form from Michał Załęcki: https://gist.github.com/MichalZalecki/e4119f95c0b7fba2d51c

patternmatching.ts

class MatchError extends Error {
}

function match<T, S>(value:T) {
    let result:(_:T)=>S;
    const context = {
        caseOf(predicate:(value:T) => boolean, payload:(_:T)=>S) {
            if (!result && predicate(value)) result = payload;
            return context;
        },
        _(payload:(_:T)=>S) {
            if (!result) result = payload;
            return context;
        },
        resolve(): S {
            if (!result) {
                throw new MatchError;
            }
            return result(value);
        }
    };
    return context;
}