Difference between revisions of "FSharp"
From ScienceZero
(→Pattern matching) |
(→Arrays) |
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==Arrays== | ==Arrays== | ||
− | let a = [|1;2;3|] | + | let a = [|1;2;3;4|] |
+ | let b = a.[2] // This will set b to 3 | ||
+ | let c = a.[1..2] // This will set c to [|2;3|] | ||
+ | let d = a.[..2] // This will set d to [|1;2;3|] | ||
+ | let e = a.[1..] // This will set e to [|2;3;4|] | ||
==Lists== | ==Lists== |
Revision as of 08:24, 23 August 2013
Contents
Values and Variables
let a = 2 This is a value and it is constant within the scope of the value. You can safely pass values to other threads, computers or to the other side of the world. Always use values instead of variables when possible.
let mutable b = 2 This is a variable and it can be updated with a new value like in other laguanges b <- b + 1
Types
The compiler will infer types in most cases. let a = 7 - 32 bit integer let b = "Hello" - String let c = 3.1415 - 64 bit floating-point
In some cases it is not possible to infer the type or you want to make a point out of it. let a = (xPos : uint64)
A function may not always have something to return, it can then return the Option type. if isByteReady then Some (readByte) else None
A tuple is an ordered collection of types. let point = 100,150 The compiler will infer point as two integers. The tuple can be decomposed by let x,y = point
Type Suffix .NET Type Range byte uy System.Byte 0 to 255 sbyte y System.SByte −128 to 127 int16 s System.Int16 −32 768 to 32 767 uint16 us System.UInt16 0 to 65 535 int, int32 System.Int32 −231 to 231 − 1 uint32 u System.UInt32 0 to 232 − 1 int64 L System.Int64 −263 to 263 − 1 uint64 UL System.UInt64 0 to 264 − 1 float System.Double 64 bit floating-point IEEE 64, approximately 15 significant digits. float32 f System.Single 32 bit floating-point IEEE 32, approximately 7 significant digits. decimal M System.Decimal A fixed-precision floating-point type with precisely 28 digits of precision. BigInteger I System.Numerics Arbitrary-sized integers Complex System.Numerics Complex numbers, let (c : Complex) = new Complex(1.0, 2.0)
Functions
Everything is a function and returns a value. Functions have only one exit.
This is a function called max that takes two integers as input and returns the larger of them. let max a b = if a > b then a else b It uses if as a function.
If it makes no sense for a function to return a value it should return a value of type unit let a = ()
If the value returned from a function is not required it can be deleted by using the ignore function. like this ignore (max 1 3)
Recuresive functions must be defined with the rec keyword. This recursive function counts down from n to 0 let rec count n = printfn "%A" n if n = 0 then 0 else count (n - 1)
Loops
Try to avoid loops when it is simple to do so because most loops require change of state to terminate and change of state is an opportunity for bugs.
let mutable i = 0 while(i < 3) do printfn "Hello World" i <- i + 1
for i = 1 to 10 do printfn "%A" i
// This type of loop is quite safe let arr = ["One";"Two";"Three"] for t in arr do printfn "%A" t //Shorter version for t in ["One";"Two";"Three"] do printfn "%A" t
Pattern matching
Pattern matching should be used in all cases where a simple if is not enough. _ is a wildcard and matches anything
// Special case as look up table let binDigit = function | "0" -> Some 0 | "1" -> Some 1 | _ -> None
// General syntax let fTest fn = match fn with | None -> "File not found" | Some(n) -> "File '%A' was found" n
Arrays
let a = [|1;2;3;4|] let b = a.[2] // This will set b to 3 let c = a.[1..2] // This will set c to [|2;3|] let d = a.[..2] // This will set d to [|1;2;3|] let e = a.[1..] // This will set e to [|2;3;4|]
Lists
let a = [1;2;3]