Practical F#

Practical F#
Ryan Riley
Catapult Systems, Inc.
Houston TechFest 2009

Agenda
Core Concepts
Basic Syntax
Why Consider F#
When to use F#
When not to use F#
Summary

Core Concepts

F# Paradigms
Functional
Object-oriented
Language-oriented

Functional Programming Concepts
First-Class Functions (and Events)
Strong Type Inference
Immutability
Make side-effects explicit (the M-word)
Functional Reactive Programming
Easy Concurrency
Actor-model Messaging (similar to Erlang)
Lazy Evaluation

Basic Syntax

let
Similar to var in C#.

Tuples
Type-safe collection of values
C# out parameters are returned as tuples

Class Declaration

Abstract Classes

Interfaces

Inheritance

Records
But then, why bother?

Discriminated Unions
Functional inheritance

Pattern Matching

Extension Methods

Object Expressions

Control Flow with Pipes

Function Composition

Computation Workflows

Quotations
This is supposed to be a practical discussion!
Quotations are similar to LINQ Expressions.

Visual Studio Integration

Why Consider F#?
You can do everything you did in C# within F#
Some things are simpler, some harder
Simpler: many OO design patterns
Simpler: Asynchronous tasks
Harder: GUI programming
Terrific for specialized tasks (polyglot)
Many great F# libraries
Terse language = fewer lines of code = $ saved

When to use F#
Asynchronous operations
Concurrent operations
Messaging (MailboxProcessor)
Transformation operations (like SSIS)
Computation-intensive operations (like SSAS)
Creating Domain Specific Languages (DSLs)
Aspect-Oriented Programming (AOP)
Testing

FP vs. OOP

#1 Reason to use F#
Your entire application is already just a series of LINQ statements!

Testing
FsTest
FsUnit

Generate Test Data

Mathematical Calculations
Project Euler Problem 4:
Project Euler Problem 3:
Project Euler Problem 6

Excel Financial Functions

Parsers
FSharp.PowerPack has a lexer and parser
Fparsec
Cashel

Automated Builds with Fake

Async Workflows

Async Workflows from C#

Functional AOP?

When not to use F#
Just want to use the newest thing
GUI programming
You can do it
Can’t use the designers
Can still be a great tool
When you are already proficient in C# and are focused almost entirely on OOP.
Stick to what you know. You’ll be faster.

Summary
“Write tomorrow’s legacy code today with C#”
Chris Smith’s F# Facts
Try F#
Fall in love with F#
Use F#
The End

Resources
F# is still CTP
Try it in VS2010 Beta 1
Or use the VS2008 CTP installer
Read books
Foundations of F#(Pickering)
Expert F# (Syme)
Functional Programming for the Real World (Petricek and Skeet)
F# for Scientists (Harrop)

Resources
http://channel9.msdn.com/pdc2008/TL11/
http://tomasp.net/blog/fsharp-webcast-functional.aspx
http://lorgonblog.spaces.live.com/blog/
http://codebetter.com/blogs/matthew.podwysocki/default.aspx

The end …

Monads
Monads are about function composition.
Take a monoid:f(x) -> xg(x) -> xf(g(x)) -> x
f.g x -> x
Add a transformation:f(x) -> Mxg(x) -> Mxf(g(x)) -> Mx
f.g x -> Mx

Creating Monadic Builders
The parts of a monad:(in F#, this would be a workflow builder)
x.Let (value, transform): sets a value, like LINQ’s Select().
x.Bind (value, transform): splits the value from the transform and passes it into the next function, like LINQ’s SelectMany().
x.Return (value): returns the result.
x.Delay (transform): kicks off the workflow.

Computation workflow structure
Typical structure of a workflow builder:type WorkflowBuilder () = member x.Bind (value, transform) = transform value member x.Return (value) = fun () -> value member x.Delay (transform) = fun () -> transform ()let workflow = new WorkflowBuilder()
Execute like so:let myWorkflow = workflow { let x = 1 // x.Let let! y = 2 // x.Bind return x + y // x.Return }let result = myWorkflow () // x.Delay

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Practical F#

by Ryan Riley

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