failwith causes an error when used in a calculation expression - FParsec












0















I use a function:



let identifier kind =
(many1Satisfy2L isLetter
(fun c -> isLetter c || isDigit c) "identifier"
>>= fun s -> preturn s) >>= fun s -> identifierKind s kind


The kind argument is of this type:



type KindOfIdentifier =
| Data
| Type
| Module


And here is my function that analyzes the kind argument:



let private identifierKind (id: string) kind =
match kind with
| KindOfIdentifier.Data ->
if id.ToUpper() = id && id.Length > 1 then preturn id
elif System.Char.IsUpper id.[0] = false then preturn id
else failwith "Error 1"
| KindOfIdentifier.Module ->
if System.Char.IsUpper id.[0] then preturn id
else failwith "Error 2"
| KindOfIdentifier.Type ->
preturn id


I would therefore like to analyze an identifier to verify whether it meets the criteria of the identifier type. If identifying it does not meet the criterion, I return an error with failwith.
But, when I use this parser (identify) with a deliberate error in my text to be analyzed, to check if everything works, I get a long error:



enter image description here



(Sorry, I'm French, so there's a little french in the error message ^^.)



How to prevent all this, and only display the error message in the classic way with FParsec?










share|improve this question



























    0















    I use a function:



    let identifier kind =
    (many1Satisfy2L isLetter
    (fun c -> isLetter c || isDigit c) "identifier"
    >>= fun s -> preturn s) >>= fun s -> identifierKind s kind


    The kind argument is of this type:



    type KindOfIdentifier =
    | Data
    | Type
    | Module


    And here is my function that analyzes the kind argument:



    let private identifierKind (id: string) kind =
    match kind with
    | KindOfIdentifier.Data ->
    if id.ToUpper() = id && id.Length > 1 then preturn id
    elif System.Char.IsUpper id.[0] = false then preturn id
    else failwith "Error 1"
    | KindOfIdentifier.Module ->
    if System.Char.IsUpper id.[0] then preturn id
    else failwith "Error 2"
    | KindOfIdentifier.Type ->
    preturn id


    I would therefore like to analyze an identifier to verify whether it meets the criteria of the identifier type. If identifying it does not meet the criterion, I return an error with failwith.
    But, when I use this parser (identify) with a deliberate error in my text to be analyzed, to check if everything works, I get a long error:



    enter image description here



    (Sorry, I'm French, so there's a little french in the error message ^^.)



    How to prevent all this, and only display the error message in the classic way with FParsec?










    share|improve this question

























      0












      0








      0








      I use a function:



      let identifier kind =
      (many1Satisfy2L isLetter
      (fun c -> isLetter c || isDigit c) "identifier"
      >>= fun s -> preturn s) >>= fun s -> identifierKind s kind


      The kind argument is of this type:



      type KindOfIdentifier =
      | Data
      | Type
      | Module


      And here is my function that analyzes the kind argument:



      let private identifierKind (id: string) kind =
      match kind with
      | KindOfIdentifier.Data ->
      if id.ToUpper() = id && id.Length > 1 then preturn id
      elif System.Char.IsUpper id.[0] = false then preturn id
      else failwith "Error 1"
      | KindOfIdentifier.Module ->
      if System.Char.IsUpper id.[0] then preturn id
      else failwith "Error 2"
      | KindOfIdentifier.Type ->
      preturn id


      I would therefore like to analyze an identifier to verify whether it meets the criteria of the identifier type. If identifying it does not meet the criterion, I return an error with failwith.
      But, when I use this parser (identify) with a deliberate error in my text to be analyzed, to check if everything works, I get a long error:



      enter image description here



      (Sorry, I'm French, so there's a little french in the error message ^^.)



      How to prevent all this, and only display the error message in the classic way with FParsec?










      share|improve this question














      I use a function:



      let identifier kind =
      (many1Satisfy2L isLetter
      (fun c -> isLetter c || isDigit c) "identifier"
      >>= fun s -> preturn s) >>= fun s -> identifierKind s kind


      The kind argument is of this type:



      type KindOfIdentifier =
      | Data
      | Type
      | Module


      And here is my function that analyzes the kind argument:



      let private identifierKind (id: string) kind =
      match kind with
      | KindOfIdentifier.Data ->
      if id.ToUpper() = id && id.Length > 1 then preturn id
      elif System.Char.IsUpper id.[0] = false then preturn id
      else failwith "Error 1"
      | KindOfIdentifier.Module ->
      if System.Char.IsUpper id.[0] then preturn id
      else failwith "Error 2"
      | KindOfIdentifier.Type ->
      preturn id


      I would therefore like to analyze an identifier to verify whether it meets the criteria of the identifier type. If identifying it does not meet the criterion, I return an error with failwith.
      But, when I use this parser (identify) with a deliberate error in my text to be analyzed, to check if everything works, I get a long error:



      enter image description here



      (Sorry, I'm French, so there's a little french in the error message ^^.)



      How to prevent all this, and only display the error message in the classic way with FParsec?







      exception f# fparsec






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked Jan 2 at 16:17









      FoxyFoxy

      251313




      251313
























          1 Answer
          1






          active

          oldest

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          2














          The failwith function throws a .NET exception - a catasprophic failure that is supposed to indicate that the program broke in an unexpected way. Or, in other words, in an exceptional way - hence the name "exception". This is not what you're trying to do.



          What you're trying to do here is to indicate to FParsec that the current parsing attempt has failed, and possibly provide an explanation of what exactly happened.



          To do this, you need to create an error-producing instance of Parser - the same type that is returned by preturn.



          While preturn creates a successful instance of Parser, there is another function that creates an error-producing instance. This function is called fail. Just use it:



              | KindOfIdentifier.Data ->
          if id.ToUpper() = id && id.Length > 1 then preturn id
          elif System.Char.IsUpper id.[0] = false then preturn id
          else fail "Error 1"





          share|improve this answer























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            1 Answer
            1






            active

            oldest

            votes








            1 Answer
            1






            active

            oldest

            votes









            active

            oldest

            votes






            active

            oldest

            votes









            2














            The failwith function throws a .NET exception - a catasprophic failure that is supposed to indicate that the program broke in an unexpected way. Or, in other words, in an exceptional way - hence the name "exception". This is not what you're trying to do.



            What you're trying to do here is to indicate to FParsec that the current parsing attempt has failed, and possibly provide an explanation of what exactly happened.



            To do this, you need to create an error-producing instance of Parser - the same type that is returned by preturn.



            While preturn creates a successful instance of Parser, there is another function that creates an error-producing instance. This function is called fail. Just use it:



                | KindOfIdentifier.Data ->
            if id.ToUpper() = id && id.Length > 1 then preturn id
            elif System.Char.IsUpper id.[0] = false then preturn id
            else fail "Error 1"





            share|improve this answer




























              2














              The failwith function throws a .NET exception - a catasprophic failure that is supposed to indicate that the program broke in an unexpected way. Or, in other words, in an exceptional way - hence the name "exception". This is not what you're trying to do.



              What you're trying to do here is to indicate to FParsec that the current parsing attempt has failed, and possibly provide an explanation of what exactly happened.



              To do this, you need to create an error-producing instance of Parser - the same type that is returned by preturn.



              While preturn creates a successful instance of Parser, there is another function that creates an error-producing instance. This function is called fail. Just use it:



                  | KindOfIdentifier.Data ->
              if id.ToUpper() = id && id.Length > 1 then preturn id
              elif System.Char.IsUpper id.[0] = false then preturn id
              else fail "Error 1"





              share|improve this answer


























                2












                2








                2







                The failwith function throws a .NET exception - a catasprophic failure that is supposed to indicate that the program broke in an unexpected way. Or, in other words, in an exceptional way - hence the name "exception". This is not what you're trying to do.



                What you're trying to do here is to indicate to FParsec that the current parsing attempt has failed, and possibly provide an explanation of what exactly happened.



                To do this, you need to create an error-producing instance of Parser - the same type that is returned by preturn.



                While preturn creates a successful instance of Parser, there is another function that creates an error-producing instance. This function is called fail. Just use it:



                    | KindOfIdentifier.Data ->
                if id.ToUpper() = id && id.Length > 1 then preturn id
                elif System.Char.IsUpper id.[0] = false then preturn id
                else fail "Error 1"





                share|improve this answer













                The failwith function throws a .NET exception - a catasprophic failure that is supposed to indicate that the program broke in an unexpected way. Or, in other words, in an exceptional way - hence the name "exception". This is not what you're trying to do.



                What you're trying to do here is to indicate to FParsec that the current parsing attempt has failed, and possibly provide an explanation of what exactly happened.



                To do this, you need to create an error-producing instance of Parser - the same type that is returned by preturn.



                While preturn creates a successful instance of Parser, there is another function that creates an error-producing instance. This function is called fail. Just use it:



                    | KindOfIdentifier.Data ->
                if id.ToUpper() = id && id.Length > 1 then preturn id
                elif System.Char.IsUpper id.[0] = false then preturn id
                else fail "Error 1"






                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Jan 2 at 16:44









                Fyodor SoikinFyodor Soikin

                43.7k569101




                43.7k569101
































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