Define a parser that consumes a single character

[mrange]

If the input is non empty the parser should return the first character.

If the input is empty the parser return a failure.

let p : Parser<char> = char

[vlukash]

Pushed a few *fs files to the repo with implementation for the single character parser but not sure if that is correct. Could you please take a look?

[mrange]

What is missing is that it should return the unconsumed part of the string. In addition error message should be associated with a position in the string in order to help the user

On Tue, Nov 1, 2016 at 8:51 AM +0100, "Volodymyr Lukashevych" [email protected] wrote:

Pushed a few *fs files to the repo with implementation for the single character parser but not sure if that is correct. Could you please take a look?

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#2 (comment)

[vlukash]

Pushed changes to a hardcoded char parser so now returning an unconsumed string on Success.

But not sure if I got the point about providing information on a position in the string in a Failure case.
As if there is no matching character in a string then we can't provide details on position. Or Probably I've missed something

type Result<'T> =
     | Success of 'T*string 
     | Failure of string 

let parseFirstCharHardcodedA str =
    let charToMatch = 'a'
    if String.IsNullOrEmpty(str) then
        Failure "Input is empty"
    else
        let firstChar = str.[0]
        if firstChar = charToMatch then
            Success(charToMatch,str.[1..])
        else
            let errorMessage = sprintf "Expected character is: '%c' but received '%c'" charToMatch firstChar
            Failure errorMessage