How find integer in text - string

Question

Help me figure out how to work with text
i have a string like: "word1 number: word2" for example : "result 0: Good" or "result 299: Bad"
i need print Undefined/Low or High
When string is null , print Undefined
When number 0-15, print Low
When number >15, print High
type GetResponse =
{
MyData: string voption
ErrorMessage: string voption }
val result: Result<GetResponse, MyError>
and then i try:
MyData =
match result with
| Ok value ->
if (value.Messages = null) then
ValueSome "result: Undefined"
else
let result =
value.Messages.FirstOrDefault(
(fun x -> x.ToUpperInvariant().Contains("result")),
"Undefined"
)
if (result <> "Undefined") then
ValueSome result
else
errors.Add("We don't have any result")
ValueNone
| Error err ->
errors.Add(err.ToErrorString)
ValueNone
ErrorMessage =
if errors.Any() then
(errors |> String.concat ", " |> ValueSome)
else
ValueNone
but i dont know gow check in string number and maybe there is some way print this without a billion if?

Answer 1

Parsing gets complex very quickly. I recommend using FParsec to simplify the logic and avoid errors. A basic parser that seems to meet your needs:
open System
open FParsec
let parseWord =
manySatisfy Char.IsLetter
let parseValue =
parseWord // parse any word (e.g. "result")
>>. spaces1 // skip whitespace
>>. puint32 // parse an unsigned integer value
.>> skipChar ':' // skip colon character
.>> spaces // skip whitespace
.>> parseWord // parse any word (e.g. "Good")
You can then use it like this:
type ParserResult = Undefined | Low | High
let parse str =
if isNull str then Result.Ok Undefined
else
match run parseValue str with
| Success (num, _ , _) ->
if num <= 15u then Result.Ok Low
else Result.Ok High
| Failure (errorMsg, _, _) ->
Result.Error errorMsg
parse null |> printfn "%A" // Ok Undefined
parse "result 0: Good" |> printfn "%A" // Ok Low
parse "result 299: Bad" |> printfn "%A" // Ok High
parse "invalid input" |> printfn "%A" // Error "Error in Ln: 1 Col: 9 ... Expecting: integer number"
There's definitely a learning curve with FParsec, but I think it's worth adding to your toolbelt.

Answer 2

I agree with Brian that parsing can become quite tricky very quickly. However if you have some well established format of the input and you're not very much into writing complex parsers, good old regular expressions can be of service ;)
Here is my take on the problem - please note that it has plenty of room to improve, this is just a proof of concept:
open System.Text.RegularExpressions
let test1 = "result 0: Good"
let test2 = "result 299: Bad"
let test3 = "some other text"
type ParserResult =
| Undefined
| Low of int
| High of int
let (|ValidNumber|_|) s =
//https://learn.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.regex?view=net-6.0
let rx = new Regex("(\w\s+)(\d+)\:(\s+\w)")
let matches = rx.Matches(s)
if matches.Count > 0 then
let groups = matches.[0].Groups |> Seq.toList
match groups with
| [_; _; a; _] -> Some (int a.Value)
| _ -> None
else
None
let parseMyString str =
match str with
| ValidNumber n when n < 16 -> Low n
| ValidNumber n -> High n
| _ -> Undefined
//let r = parseMyString test1
printfn "%A" (parseMyString test1)
printfn "%A" (parseMyString test2)
printfn "%A" (parseMyString test3)
The active pattern ValidNumber returns the Some number if a match of the input string is found, otherwise it returns None. The parseMyString function uses the pattern and guards to initialise the final ParserOutput value.