not inferring expression signature match on generics

[Samsinite]

TypeScript Version: 3.5.2

Search Terms: no compatible call signatures

Code

  type Success<T> = {
    tag: 'success';
    value: T;
    fbind<R, E>(func: (value: T) => Result<R, E>) : Result<R, E>;
  }
  
  type Failure<E> = {
    tag: 'failure';
    error: E;
    fbind<T, R>(_func: (value: T) => Result<R, E>) : Result<R, E>;
  }
  
  type Result<T, E> = Success<T> | Failure<E>;
  
  function success<T>(value: T) : Success<T> {
    return {
      tag: 'success',
      value,
      fbind<R, E>(func: (value: T) => Result<R, E>): Result<R, E> {
        return func(this.value);
      },
    };
  }
  
  function failure<E>(error: E) : Failure<E> {
    return {
      tag: 'failure',
      error,
      fbind<T, R>(_func: (value: T) => Result<R, E>) : Result<R, E> {
        return this;
      },
    };
  }
  
  type ValidationError = string;
  
  function parseDate(value: string) : Result<Date, ValidationError> {
    // simple example to show issue
    return success(new Date(value));
  }
  
  function logDate(date: Date) : Result<Date, ValidationError> {
    console.log('Date: ', date);
    return success(date);
  }
  
  parseDate('1-1-2019').fbind(logDate);

But, the following code runs without errors, which is strange:

const result = parseDate('1-1-2019');

if (result.tag === 'success') { 
  result.fbind(logDate);
} else if (result.tag === 'failure') { 
  result.fbind(logDate);
}

Expected behavior: No errors

Actual behavior: Cannot invoke an expression whose type lacks a call signature. Type '(<R, E>(func: (value: Date) => Result<R, E>) => Result<R, E>) | (<T, R>(_func: (value: T) => Result<R, string>) => Result<R, string>)' has no compatible call signatures.

Playground Link: http://www.typescriptlang.org/play/#code/C4TwDgpgBAygrgYwRAzigPAFQHxQLxQDeUAUFFMAIYDmAXFAOQqLJoMDcZUAbpQDZwI9TJ3IAzAEYBLAHYATdACUANFACi2ABRi4MhPU28BQqJgCU+XItRw+wJao0X615nYfrsnAL4kSoSCgAMUopAQAnCHQNfCJScio6RjFQiIgOLghw8IB7cPo1UShJWQVMVUUtAH0dPQMjQWELPCsbdxVPZyhXW3sOjR8-AOge93LPWPgkVAwcKAAfYNS4SOivP1qEYCkcmShmabQsLQaTcyh6KdZZ3GIuSOAVvbvyBJp6JhYZhmUuclPfq9itJ5B4NNpdPooIZ+I1TM1Wm4+o5sGYXG1kRMXkCoA8nsVIZpgAALKQoAB0pzMRXI3kBUG8gxIm22u2Ky1W4KyuXy6i6ITCKyiMWxePCz3ir0SHxSgsiPz+UG5eXp4hBZQq1U29VhZwR3QxYNRFwNSKNcUV5DFexJZJpDPpjJIvn84GgADV+FI5JRWTI1Nk8rEUMBwrJqJxmZC-VAwJRwigIAARX0QGHGeghsMyahdUb2FPACCqT18b2+nb+wPhW6SgD0df2UgAtmA+NAIAAPSit9sUHL7Yk5ADuUDJzAg9wgj3F+y+aE0Mggo8LabMZmdG2jlagfBy1FXmh9Rfoq7zhtXJa9x8rAZ5ta4CF2KBy7fJe+omgYq4+qmPEGpKcZz2A5riPVNAJdOME2TVMvwARgAWiQgAmAAGeCAE4GDMckSnkTQPzPSMnxkENcQxWJoMTQ8GCQ1CMOwwCSCkMRoUiJFyUSfA8AIT5DhQHCLStDE8PVQj92I50lT4RMxzYzQON6LiaB4vjZTSITRVE-C5Akg8IJ8IA

Related Issues: None that I could find

[jcalz]

Duplicate of #7294

Despite more support added for calling unions of functions in TS3.3, it is still not possible to call unions of multiple generic function signatures. It's not trivial to implement that.

[Samsinite]

Is there an issue that is open for this feature? Unless support for this is not planned, seems like it would be a good idea to keep an issue open for tracking this issue/feature, thoughts?

[RyanCavanaugh]

Issues are open if they have identifiable near-term work to do, which isn't the case here.