swlaschin

The duplicate #load problem and how to fix it

Symptom: A weird error such as:

error FS0001: This expression was expected to have type
    'FSI_0011.MyType'
but here has type
    'FSI_0012.MyType'

swlaschin

"What is a functional approach to logging and transactions" is a question I get asked sometimes. So here's my take.

First, there is never a perfect answer! It depends on your tolerance for impurity, what's compatible with the rest of the code and what other maintainers expect.

Logging

I use F#, which generally has a pragmatic approach to this kind of thing.

In Haskell or purist FP Scala (e.g. with Cats/Scalaz) the standard approach would be to use a writer monad, but for F#/OCaml/ReasonML etc, that would probably be overkill.

swlaschin

Setup instructions for the 16 hr (2 full day or 4 half day) Domain Modeling Made Functional workshop

Requirements:

• Git (optional)
• F#

I will assume that you have git already installed.

Install F#

• Instructions for Visual Studio and VS Code.

swlaschin

How to find F# jobs

People often ask me how to find F# jobs. I don't have any special connections to companies using F#, and I don't have any special tricks either. I wish I did!

So, given that, here's my take on F# jobs.

Job hunting

For job hunting my suggestions are:

swlaschin

Some recommended books for improving as a software developer

Most software books are too language specific and go out of date too quickly. What I find has stayed with me are books about bigger concepts, such as systems thinking and complexity, and also so-called "soft skills" such as management and psychology.

User experience

These are all really about developing empathy for other people :)

• "The Design of Everyday Things" by Donald Norman

swlaschin

(*
Demonstrates DTO validation for a news feed domain
*)

// "result.fsx" comes from https://github.com/swlaschin/DmmfWorkshop/blob/master/src/E-ModelingErrors/Result.fsx
#load "result.fsx"

module Domain =
    type DocumentId = DocumentId of int
    type EmailAddress = EmailAddress of string

swlaschin

module Util =

    /// Merge a new list into an old list.
    /// The sortKey is used to sort and compare the keys.
    /// The insert/update/delete actions are called as appropriate. They return Options so that
    /// you can filter at the same time.
    let merge oldList newList sortKey insertAction updateAction deleteAction =

        let rec innerMerge oldList newList =
            match oldList,newList with

swlaschin

Tips on exposing F# to C#

Api and Methods

I suggest that you create one or more Api.fs files to expose F# code in a C# friendly way.

In this file:

• Define functions with PascalCase names. They will appear to C# as static methods.
• Functions should use tuple-style declarations (like C#) rather than F#-style params with spaces.

swlaschin

F# equivalents to C# LINQ functions

See also https://fsharpforfunandprofit.com/posts/list-module-functions/

Converting each item

// ------------------------------
// add 1 to each item
// ------------------------------

swlaschin

Functional Track talks from NDC 2014-2017

• Functional Track talks from NDC Oslo 2014
• Functional Track talks from NDC London 2014
• Functional Track talks from NDC Oslo 2015
• Functional Track talks from NDC London 2016
• Functional Track talks from NDC Oslo 2016
• Functional Track talks from NDC London 2017
• Functional Track talks from NDC Oslo 2017