byethrow
  • English

      • Debugging

      When debugging complex pipelines, you need to see what's happening at each step. The inspect and inspectError functions let you peek at values without affecting the flow.

      inspect - Peek at Success Values

      inspect runs a side effect function on success values but always returns the original result unchanged:

      import { 
      import Result
      Result       } from '@praha/byethrow';      

const 
      const result: Result.Result<number, never>
      result       = 
      import Result
      Result      .
      const pipe: <Result.Result<42, never>, Result.Result<42, never>, Result.Result<number, never>>(a: Result.Result<42, never>, ab: (a: Result.Result<42, never>) => Result.Result<42, never>, bc: (b: Result.Result<42, never>) => Result.Result<number, never>) => Result.Result<number, never> (+25 overloads)
      pipe      (      
  
      import Result
      Result      .
      const succeed: <42>(value: 42) => Result.Result<42, never> (+1 overload)
      succeed      (42),      
  
      import Result
      Result      .
      const inspect: <Result.Result<42, never>, void>(fn: (a: 42) => void) => (result: Result.Result<42, never>) => Result.Result<42, never> (+1 overload)
      inspect      ((
      value: 42
      value      ) => 
      var console: Console
      console      .
      Console.log(...data: any[]): void
      The console.log() static method outputs a message to the console.
      

      MDN Reference
      log      ('Value:', 
      value: 42
      value      )),      
  
      import Result
      Result      .
      const map: <Result.Result<42, never>, number>(fn: (a: 42) => number) => (result: Result.Result<42, never>) => Result.Result<number, never> (+1 overload)
      map      ((
      x: 42
      x      ) => 
      x: 42
      x       * 2),      
);
// Console: "Value: 42"
// { type: 'Success', value: 84 }

      On failure, inspect does nothing:

      import { 
      import Result
      Result       } from '@praha/byethrow';      

const 
      const result: Result.Result<never, "error">
      result       = 
      import Result
      Result      .
      const pipe: <Result.Result<never, "error">, Result.Result<never, "error">>(a: Result.Result<never, "error">, ab: (a: Result.Result<never, "error">) => Result.Result<never, "error">) => Result.Result<never, "error"> (+25 overloads)
      pipe      (      
  
      import Result
      Result      .
      const fail: <"error">(error: "error") => Result.Result<never, "error"> (+1 overload)
      fail      ('error'),      
  
      import Result
      Result      .
      const inspect: <Result.Result<never, "error">, void>(fn: (a: never) => void) => (result: Result.Result<never, "error">) => Result.Result<never, "error"> (+1 overload)
      inspect      ((
      value: never
      value      ) => 
      var console: Console
      console      .
      Console.log(...data: any[]): void
      The console.log() static method outputs a message to the console.
      

      MDN Reference
      log      ('Value:', 
      value: never
      value      )), // Not called      
);
// { type: 'Failure', error: 'error' }

      inspectError - Peek at Error Values

      inspectError is the counterpart for failure values:

      import { 
      import Result
      Result       } from '@praha/byethrow';      

const 
      const result: Result.Result<never, "Something went wrong">
      result       = 
      import Result
      Result      .
      const pipe: <Result.Result<never, "Something went wrong">, Result.Result<never, "Something went wrong">>(a: Result.Result<never, "Something went wrong">, ab: (a: Result.Result<never, "Something went wrong">) => Result.Result<never, "Something went wrong">) => Result.Result<never, "Something went wrong"> (+25 overloads)
      pipe      (      
  
      import Result
      Result      .
      const fail: <"Something went wrong">(error: "Something went wrong") => Result.Result<never, "Something went wrong"> (+1 overload)
      fail      ('Something went wrong'),      
  
      import Result
      Result      .
      const inspectError: <Result.Result<never, "Something went wrong">, void>(fn: (a: "Something went wrong") => void) => (result: Result.Result<never, "Something went wrong">) => Result.Result<never, "Something went wrong"> (+1 overload)
      inspectError      ((
      error: "Something went wrong"
      error      ) => 
      var console: Console
      console      .
      Console.error(...data: any[]): void
      The console.error() static method outputs a message to the console at the "error" log level. The message is only displayed to the user if the console is configured to display error output. In most cases, the log level is configured within the console UI. The message may be formatted as an error, with red colors and call stack information.
      

      MDN Reference
      error      ('Error:', 
      error: "Something went wrong"
      error      )),      
);
// Console: "Error: Something went wrong"
// { type: 'Failure', error: 'Something went wrong' }

      On success, inspectError does nothing:

      import { 
      import Result
      Result       } from '@praha/byethrow';      

const 
      const result: Result.Result<42, never>
      result       = 
      import Result
      Result      .
      const pipe: <Result.Result<42, never>, Result.Result<42, never>>(a: Result.Result<42, never>, ab: (a: Result.Result<42, never>) => Result.Result<42, never>) => Result.Result<42, never> (+25 overloads)
      pipe      (      
  
      import Result
      Result      .
      const succeed: <42>(value: 42) => Result.Result<42, never> (+1 overload)
      succeed      (42),      
  
      import Result
      Result      .
      const inspectError: <Result.Result<42, never>, void>(fn: (a: never) => void) => (result: Result.Result<42, never>) => Result.Result<42, never> (+1 overload)
      inspectError      ((
      error: never
      error      ) => 
      var console: Console
      console      .
      Console.error(...data: any[]): void
      The console.error() static method outputs a message to the console at the "error" log level. The message is only displayed to the user if the console is configured to display error output. In most cases, the log level is configured within the console UI. The message may be formatted as an error, with red colors and call stack information.
      

      MDN Reference
      error      ('Error:', 
      error: never
      error      )), // Not called      
);
// { type: 'Success', value: 42 }

      Example: Trace the Pipeline

      import { 
      import Result
      Result       } from '@praha/byethrow';      

const 
      const processData: (input: Input) => Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">
      processData       = (
      input: Input
      input      : 
      type Input = {
    data: string;
}
      Input      ) => {      
  return 
      import Result
      Result      .
      const pipe: <Result.Result<Input, never>, Result.Result<Input, never>, Result.Result<Input, "ValidateFailed">, Result.Result<Input, "ValidateFailed">, Result.Result<Transformed, "ValidateFailed" | "TransformFailed">, Result.Result<Transformed, "ValidateFailed" | "TransformFailed">, Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">, Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">, Result.Result<...>>(a: Result.Result<...>, ab: (a: Result.Result<...>) => Result.Result<...>, bc: (b: Result.Result<...>) => Result.Result<...>, cd: (c: Result.Result<...>) => Result.Result<...>, de: (d: Result.Result<...>) => Result.Result<...>, ef: (e: Result.Result<...>) => Result.Result<...>, fg: (f: Result.Result<...>) => Result.Result<...>, gh: (g: Result.Result<...>) => Result.Result<...>, hi: (h: Result.Result<...>) => Result.Result<...>) => Result.Result<...> (+25 overloads)
      pipe      (      
    
      import Result
      Result      .
      const succeed: <Input>(value: Input) => Result.Result<Input, never> (+1 overload)
      succeed      (
      input: Input
      input      ),      
    
      import Result
      Result      .
      const inspect: <Result.Result<Input, never>, void>(fn: (a: Input) => void) => (result: Result.Result<Input, never>) => Result.Result<Input, never> (+1 overload)
      inspect      ((
      value: Input
      value      ) => 
      var console: Console
      console      .
      Console.log(...data: any[]): void
      The console.log() static method outputs a message to the console.
      

      MDN Reference
      log      ('Input:', 
      value: Input
      value      )),      
    
      import Result
      Result      .
      const andThrough: <Result.Result<Input, never>, Result.Result<Input, "ValidateFailed">>(fn: (a: Input) => Result.Result<Input, "ValidateFailed">) => (result: Result.Result<Input, never>) => Result.Result<Input, "ValidateFailed"> (+1 overload)
      andThrough      (
      const validate: (input: Input) => Result.Result<Input, "ValidateFailed">
      validate      ),      
    
      import Result
      Result      .
      const inspect: <Result.Result<Input, "ValidateFailed">, void>(fn: (a: Input) => void) => (result: Result.Result<Input, "ValidateFailed">) => Result.Result<Input, "ValidateFailed"> (+1 overload)
      inspect      ((
      value: Input
      value      ) => 
      var console: Console
      console      .
      Console.log(...data: any[]): void
      The console.log() static method outputs a message to the console.
      

      MDN Reference
      log      ('After validation:', 
      value: Input
      value      )),      
    
      import Result
      Result      .
      const andThen: <Result.Result<Input, "ValidateFailed">, Result.Result<Transformed, "TransformFailed">>(fn: (a: Input) => Result.Result<Transformed, "TransformFailed">) => (result: Result.Result<Input, "ValidateFailed">) => Result.Result<Transformed, "ValidateFailed" | "TransformFailed"> (+1 overload)
      andThen      (
      const transform: (input: Input) => Result.Result<Transformed, "TransformFailed">
      transform      ),      
    
      import Result
      Result      .
      const inspect: <Result.Result<Transformed, "ValidateFailed" | "TransformFailed">, void>(fn: (a: Transformed) => void) => (result: Result.Result<Transformed, "ValidateFailed" | "TransformFailed">) => Result.Result<Transformed, "ValidateFailed" | "TransformFailed"> (+1 overload)
      inspect      ((
      value: Transformed
      value      ) => 
      var console: Console
      console      .
      Console.log(...data: any[]): void
      The console.log() static method outputs a message to the console.
      

      MDN Reference
      log      ('After transform:', 
      value: Transformed
      value      )),      
    
      import Result
      Result      .
      const andThen: <Result.Result<Transformed, "ValidateFailed" | "TransformFailed">, Result.Result<Saved, "SaveFailed">>(fn: (a: Transformed) => Result.Result<Saved, "SaveFailed">) => (result: Result.Result<Transformed, "ValidateFailed" | "TransformFailed">) => Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed"> (+1 overload)
      andThen      (
      const save: (input: Transformed) => Result.Result<Saved, "SaveFailed">
      save      ),      
    
      import Result
      Result      .
      const inspect: <Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">, void>(fn: (a: Saved) => void) => (result: Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">) => Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed"> (+1 overload)
      inspect      ((
      value: Saved
      value      ) => 
      var console: Console
      console      .
      Console.log(...data: any[]): void
      The console.log() static method outputs a message to the console.
      

      MDN Reference
      log      ('After save:', 
      value: Saved
      value      )),      
    
      import Result
      Result      .
      const inspectError: <Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">, void>(fn: (a: "ValidateFailed" | "TransformFailed" | "SaveFailed") => void) => (result: Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed">) => Result.Result<Saved, "ValidateFailed" | "TransformFailed" | "SaveFailed"> (+1 overload)
      inspectError      ((
      error: "ValidateFailed" | "TransformFailed" | "SaveFailed"
      error      ) => 
      var console: Console
      console      .
      Console.error(...data: any[]): void
      The console.error() static method outputs a message to the console at the "error" log level. The message is only displayed to the user if the console is configured to display error output. In most cases, the log level is configured within the console UI. The message may be formatted as an error, with red colors and call stack information.
      

      MDN Reference
      error      ('Pipeline failed:', 
      error: "ValidateFailed" | "TransformFailed" | "SaveFailed"
      error      )),      
  );
};

      References

      FunctionPurpose
      inspect(fn)Run a side effect on the success value
      inspectError(fn)Run a side effect on the error value