F# for heating

8 thoughts on “F# for heating”

1. Pingback: F# Weekly #51, 2012 « Sergey Tihon's Blog
2. this is really cool 🙂

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3. Can you help to write efficient code in F# to achieve following.
   — connect to database and get dataset
   — prepare my object (i.e Person(){firstname, lastname) from this data and create a List of Person object.

   — Now whenever I need to access person details i read it from this collection. No more calls to database

   In My code i have achieved to do all of them except the last point. Every time i access Person object its going to database and reload the data 😦

   thanks in advance. is there any personal email address from you so i can contact you about some of the implementation in F# i am working on

   many thanks in advance 🙂

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   1. It is really depend on the database that you use. If you use SQL for example, you should use SqlTypeProvider. If you use Mongo, then Fsharp.Mongo will be good choice. Please share a bit more details.
      BTW. StackOverflow http://stackoverflow.com/questions/tagged/f%23 is great place for questions, there are lot of experts there.

      Reply
4. Reblogged this on D Says and commented:
   This is a real fun and let your frustration go out from your computer.

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5. thanks for the reply . Here is my code below.
   module sql
   open System
   open System.Collections.Generic
   open System.Data
   open System.Data.SqlClient
   open System.Reflection
   open System.Data.OleDb;
   open System.Text.RegularExpressions
   open Microsoft.FSharp.Reflection

   // Using records to store the data
   type Person = { FirstName:string; LastName:string; Age:int }

   let connectionString= “myDBConnectionstring”
   // Runs the specified query ‘sql’ and formats rows using function ‘f’
   let query sql f =

   seq { use cn = new SqlConnection(connectionString) // will be disposed
   let da = new SqlDataAdapter(new SqlCommand(sql, cn))
   let ds = new DataSet()
   cn.Open()
   let i = da.Fill(ds)
   let rowCol = ds.Tables.[0].Rows
   for i in 0 .. (10 – 1) do // just take 10 records for test
   yield f (rowCol.[i]) }

   let names = query “SELECT * FROM User_tbl” (fun row -> row.[“FirstName”])
   for name in names do printfn “%A” name

   names |> Seq.iter (printfn “%A”)

   Now when i access objects from “names” than its accessing the database (which i understand why as my code is written like this )
   i want to load it once only.

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   1. It is happened because the sequence is lazy. Please try to load it into list or array, like this
      let names = query “SELECT * FROM User_tbl” (fun row -> row.[“FirstName”]) |> Seq.toArray

      But, much shorter code will be with TypeProviders
      http://msdn.microsoft.com/en-us/library/hh361033.aspx

      Reply
6. Hello
   Is there something called Eval or similiar function available in F# ? i have already looked on community but could not really get a clear direction.
   Here is what i want to achieve

   type Parameter = { Paramkey:string; ParamFormula:string; ParamDefaultValue:int }

   let p1 = { Paramkey = “p1”; ParamFormula = “10”; ParamDefaultValue = 10; }
   let p2 = { Paramkey = “p2”; ParamFormula = “p1*2”; ParamDefaultValue = 20; }
   let p3 = { Paramkey = “p3”; ParamFormula = “10+(p1*3*p2)”; ParamDefaultValue = 30; }

   let ParameterList = [p1;p2;p3]
   let Formula1 = p1.ParamFormula + p2.ParamFormula +p3.ParamFormula

   let Formula2 = Formula1*10

   call Formula2

   the parameter formulas will be coming straight from some datastore .

   Reply