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match statement implementation
f#

in screwing around with quotations, i wrote a sample function that i then extracted out as a quotation. the sample function is this

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[<ReflectedDefinition>]
let public sample f_name p2 =
    let a = "a"
    let b = "b"
    
    printf "sample {%A}\r\n" f_name
    match a with
    | "" -> 
        b,a
    | "a" -> 
        a,b
    | _ -> 
        a,a

the quotation representation is this

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Let (a, Value ("a"),
     Let (b, Value ("b"),
          Sequential (Application (Let (clo1,
                                        Call (None,
                                              Microsoft.FSharp.Core.FastFunc`2[T,Microsoft.FSharp.Core.Unit] printf[FastFunc`2](Microsoft.FSharp.Text.Format`4[Microsoft.FSharp.Core.FastFunc`2[T,Microsoft.FSharp.Core.Unit],System.IO.TextWriter,Microsoft.FSharp.Core.Unit,Microsoft.FSharp.Core.Unit]),
                                              [Coerce (NewObject (Void .ctor(System.String),
                                                                  Value ("sample {%A}\r\n")),
                                                       null)]),
                                        Lambda (arg10, Application (clo1, arg10))),
                                   f_name),
                      Let (matchValue, a,
                           IfThenElse (Call (None,
                                             Boolean GenericEquality[String](System.String, System.String),
                                             [matchValue, Value ("")]),
                                       NewTuple (b, a),
                                       IfThenElse (Call (None,
                                                         Boolean GenericEquality[String](System.String, System.String),
                                                         [matchValue,
                                                          Value ("a")]),
                                                   NewTuple (a, b),
                                                   NewTuple (a, a)))))))

now, my question is - why is the match statement implemented as a set of nested ifs? and if there's no way to do something more closely resembling a switch statement, why impose the restriction that the individual patterns be constants?

.

Actually there's no such restriction

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 match arr with | _ when arr.Length > 10 -> arr |> List.of_array | _ -> []

which can be treated as

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 if arr.Length > 10 then arr |> List.of_array else []
By on 4/13/2009 6:43 AM ()

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