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Active Patterns - literal string
f#

I hit something unexpected while using active patterns. I'm trying to parse a (string*string) where each string can be either an integer or a "*". The code:

#light

module Tests

open System

let tryParseInt a =

match Int32.TryParse a with

| (false, _) -> None

| (true, x) -> Some x

let (|Integer|_|) x =

match tryParseInt x with

| None -> None

| _ -> Some ()

let rangeAll = "*"

let numericOrAll kv =

match kv with

| Integer, Integer -> true

| Integer, rangeAll -> true

| rangeAll, Integer -> true

| _ -> false

let numericOrAllLiteral kv =

match kv with

| Integer, Integer -> true

| Integer, "*" -> true

| "*", Integer -> true

| _ -> false

[<EntryPoint>]

let main param =

printf "%A\n" (numericOrAll ("abc", "1500"))

printf "%A\n" (numericOrAllLiteral ("abc", "1500"))

printf "\ndone"

Console.ReadKey() |> ignore

0

The weird thing is that numericOrAll and numericOrAllLiteral behave differently. numericOrAllLiteral behaves as expected (returning false), while numericOrAll returns true.
What am I doing wrong?

.

You will either have to use the string literal itself in your pattern matching expressions or you will have to resort to a when clause.

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let numericOrAll kv = 
    match kv with
    | Integer, Integer -> true
    | Integer, "*"     -> true
    | "*",     Integer -> true
    | _                -> false

let numericOrAll kv = 
    match kv with
    | Integer, Integer             -> true
    | Integer, x when x = rangeAll -> true
    | x, Integer when x = rangeAll -> true
    | _ -> false

See this thread for more discussion.

By on 1/13/2009 4:52 AM ()

Thanks!

By on 1/13/2009 4:59 AM ()

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