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Language Essentials Active Patterns
namespace ClassLibrary1
open System
module SingleCase =
//definition
let (|UpperCase|) (x:string) = x.ToUpper()
//PM usage
match "foo" with
| UpperCase "FOO" -> printfn " = FOO "
| a when a.ToUpper() = "FOO" -> printfn " = FOO (long form)"
| anythingElse -> printfn "%s" anythingElse
//| UpperCase thisIsUpperCase -> printfn "%s" thisIsUpperCase
//used as part of function
let usedInaFunctionSig (UpperCase(u)) =
printfn "%s" u
usedInaFunctionSig "lower"
//used as method
let usedLikeAMethod f =
let uppered = (|UpperCase|) f
printfn "%s" uppered
usedLikeAMethod "likeamethod"
//deconstruction binding
let (UpperCase deconstructed) = "lower"
printfn "%s" deconstructed
//lazy
let (|Lazy|) (x:Lazy<_>) = x.Force()
let fourtyTwo = 42
let lazyTest = lazy (fourtyTwo + 10)
match lazyTest with
| Lazy(result) -> printfn "%i" result
//properties - poormans shorthand lambda
type MyType =
{FirstProperty: string; Two: int}
let (|Fst|) (x:MyType) = x.FirstProperty
let testList = [ {FirstProperty = "test"; Two = 42}
{FirstProperty = "anotherTest"; Two = 54} ]
let firstProps1 = testList |> List.map (fun x -> match x with Fst a -> a)
let firstProps2 = testList |> List.map (function Fst a -> a)
let firstProps3 = testList |> List.map (|Fst|)
// -----------------------------------------------------------------------
module MultiCase =
let (|Odd|Even|) x =
if x % 2 = 0 then Even x
else Odd x
let (|Sentence|Word|WS|) (input : string) =
match input.Trim() with
| "" -> WS
| input when input.Contains(" ") -> Sentence (input.Split([|" "|], StringSplitOptions.None))
| everythingElse -> Word (everythingElse)
let usedLikeAMethod f =
let sentenceWordOrWS = (|Sentence|Word|WS|) f
match sentenceWordOrWS with
| Choice1Of3 _ -> "sentence"
| Choice2Of3 _ -> "word"
| Choice3Of3 _ -> "whitespace"
//-----------------------------------------------------------------------------
module PartialActive =
let (|AllAndLast|_|) (xs: 'T list) =
match xs with
| [] ->
None
| _ ->
let reversed = List.rev xs
Some (List.rev reversed.Tail, reversed.Head)
let numbers = [1..10]
match numbers with
| AllAndLast (all, last) ->
printfn "last: %A, all: %A" last all
| anyThingElse -> printfn "anything else: %A" anyThingElse
//emulator sample
let between startAddress endAddress address =
if address >= startAddress && address <= endAddress then Some() else None
let romStart, romEnd = 0xfc000u, 0xff000u
let (|Rom|_|) = between romStart romEnd
let writeToMemory location data =
match location with
| Rom -> printfn "Cannot write to %A because it is a Rom area" location
| _ -> printfn "write data here"
let (|LEA|_|) data =
//0100 rrr1 11ss sSSS
if data &&& 0b1111000111000000 = 0b0100000111000000 then
let register = byte (data >>> 9) &&& 0b111uy
let mode = byte (data >>> 3) &&& 0b111uy
let register2 = byte data &&& 0b111uy
Some(register, mode, register2)
else None
match 0b0100001111010011 with
| LEA(register, mode, register2) -> printfn "LEA %A %A %A" register mode register2
| other -> printfn "other: %u" other
//quotation sample
open Microsoft.FSharp.Quotations
open Microsoft.FSharp.Quotations.Patterns
let (|InstanceMethod|_|) (expr:Expr) =
match expr with
| Call(instance, mi, args) ->
instance |> Option.map (fun e -> (e, mi, args))
| _ -> None
let number = 42
match <@@ number.Equals 42 @@> with
| InstanceMethod(e,mi,args) -> printfn "instance method: e: %A" e
| other -> printfn "Not an instance method: %A" other
//-----------------------------------------------------------------------------
module Parameterized =
let (|Contains|_|) pattern value =
if String.IsNullOrWhiteSpace value then
None
elif value.Contains pattern then
Some()
else None
match "foo" with
| Contains "o" -> printfn "contains o"
| _ -> printfn "anything else"
//emulator sample
let romStart, romEnd = 0xfc000u, 0xff000u
let (|MemoryBetween|_|) startAddress endAddress address =
if address >= startAddress && address <= endAddress then Some() else None
let writeToMemory location data =
match location with
| MemoryBetween romStart romEnd -> printfn "Cannot write to %A because it is a Rom area" location
| _ -> printfn "write data here"
writeToMemory 0xfc001u 0x0000u
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