Fantom - Programming Language for JVM, CLR, and Javascript

Fantom

Programming language for JVM, CLR, and JS

2012, Kamil Toman
http://fantomery.org/katox/fantom-en.pdf

What Is Fantom
● Language for multiple platforms
● Object oriented
● Functional
● Balance of static and dynamic typing
● Well-known "c-like" syntax

● Opensource (AFL 3.0)

Productivity
● Literals
● Type inference
● Functions
● Closures
● Mixins
● Integration (FFI)
● DSL support

Literals
● Lists
[,]
[ 10, 20, 30 ]
[ "a", "b", [ "c", "d" ], "e" ]
● Maps
[:]
[ "x" : 10.0d, "y" : 3.14f ]
[ 10 : "x", 20 : [ "p", "q", "r" ] ]
● Types (introspection)
sys::Str#, Str#
● Slots (introspection)
Str#plus, Int#plusDecimal, Uuid#fromStr

Literals (2)
● Uri
`http://fantom.org`
`http://myserver.com/edit?n=Ron&s=Smith`
`/home/fantom/checkitout.fan`
● Duration
1ns, 1ms, 1sec, 1min, 1hr, 1day
● Range
[ 10..20, 30..<40, -3..-1 ]

Type Inference
● u := Uuid()
// u.typeof -> sys::Uuid
● s := "some string"
// s.typeof -> sys::Str
● list := [10, 20, 30]
// list.typeof -> sys::Int[]
listObj := ["a", 1]
// listObj.typeof -> sys::Obj[]
● map := ["x" : 10, "y" : 3]
// map.typeof -> [sys::Str : sys::Int]
● mapNum := ["x" : 10.0d, "y" : 3.14f]
// mapNum.typeof -> [sys::Str : sys::Num]

Functions and Closures
● Functions - signature |A a, B b, ..., H h -> R|
double := |Int a -> Int| { 2 * a }
v := |->| {}
● Methods - just functions wrappers
|Int a, Int b ->Int| plus := Int#plus.func
● Closures - expressions that return functions
Str prefix := ""
print := |Obj o -> Str| { prefix + o.toStr }
● Bind - bind parameters of existing functions
op := |Method m, Int a, Int b| { m.callOn(a, [b]) }
mul := opFunc.bind([Int#mult]) // |Int, Int->Int|
plus2 := opFunc.bind([Int#plus, 2]) // |Int -> Int|

Mixins
mixin HasColor {
abstract Str color
virtual Void sayIt() { echo ("My favourite $color") } }

mixin HasAge {
abstract Date produced
virtual Bool isVeteran() { return produced < Date.fromStr("1919-01-01") } }

class Car : HasColor, HasAge {
override Str color := "evil grey"
override Date produced := Date.today
override Void sayIt() { echo("My ${isVeteran ? "veteran" : color} car
produced ${produced.year}.") } }

Car().sayIt // -> My evil grey car produced 2012.

Java FFI
● Java
○ package => Fantom pod
○ class => Fantom class
○ interface => Fantom mixin
○ field => Fantom field
○ method => Fantom method
using [java] javax.swing
using [java] java.util::Map$Entry as Entry
f := JFrame(...)

● There are some limitations of Fantom FFI. What's not
supported
○ overloaded methods, primitive multidimensional
arrays, > 1 level deep inheritance from java classes

Javascript FFI
● source code Fantom -> Js generation (no bytecode)
@Js
class GonnaBeJs
{
Void sayHi() { Win.cur.alert("Hello!") }
}

● native peer Js -> Fantom
// Fantom
class Foo {
native Str? f
}

// Javascript
fan.mypod.FooPeer.prototype.m_f = "";
fan.mypod.FooPeer.prototype.f = function(t) { return this.m_f; }
fan.mypod.FooPeer.prototype.f$ = function(t, v) { this.m_f = v; }

DSL Support
● Ability to integrate custom language or AST
modifications of Fantom code
● Syntax - DslType <|...|>
echo(Str<|A towel, it says, is about the most massively useful thing an
interstellar hitchhiker can have.|>)

Regex<|^[a-z0-9._%+-]+@[a-z0-9.-]+.[a-z]{2,4}$|>

@Select
User getUser(Int id){
one(sql<|
select u.userid, u.name
from User u,Company c
where u.id = #{id} and u.companid = c.id and c.isdeleted = 0
|>)
}

Practical Shortcuts
● Dynamic typing
obj->foo // obj.trap("foo", [,])
● Implicit upcast
Derived derived := base
● Optional return for simple expressions
files.sort |a, b| { a.modified <=> b.modified }
● isnot keyword
alwaysFalse := "a" isnot Str
● Optional parenthesis for functions of arity 0
yes := "yes".capitalize

Practical Shortcuts (2)
● Optional function calls
tel := contact?.phone?.mobile
● Elvis operator
x ?: def // x == null ? def : x
● it-blocks
`file.txt`.toFile.eachLine { echo (it) }
// `file.txt`.toFile().eachLine(|line| { echo (line) })
● literals for data
Date.today - 1day // yesterday
● string interpolation
res.headers["Authorization"]="Basic " + "$user:$pass".
toBuf.toBase64

Declarative Style
win := Window
{
size = Size(300,200)
Label {
text = "Hello world"
halign=Halign.center },
}.open

createTable("user") {
createColumn("user_id", integer) { autoIncrement; primaryKey }
createColumn("login", varchar(64)) { notNull; unique }
createColumn("pwd", varchar(48)) { comment("Password hash"); notNull }
createColumn("role_id", integer) { notNull }
index("idx_login", ["login"])
foreignKey("fk_role", ["role_id"], references("role", ["role_id"]))
}

Declarative Style (2)
class Person {
Str? name
Str[]? emails
}
phoneBook := [
Person
{
name = "Fantom"; emails = [ "fantom@opera.org", "fantom@gmail.com" ]
},
Person
{
name = "Nobody"; emails = [ "nobody@nowhere.org", "noob@gmail.com" ]
}
]

Functional Style
["ox", "cat", "deer", "whale"].map { it.size } // -> [2, 3, 4, 5]
[2,3,4].all { it > 1 } // -> true
[2,3,4].any { it == 4 } // -> true

["hello", 25, 3.14d, Time.now].findType(Num#) // -> [25, 3.14]
[1, 1, 2, 3, 2, 1, 1].findAll |i| { i.isEven } // -> [2, 2]

[1, 1, 2, 3, 2, 1, 1].reduce([:]) |[Int:Int]r, Int v->[Int:Int]| { return r[v]=r.get(v,0)+1 }
// -> [1:4, 2:2, 3:1]

phoneBook.findAll | Person p -> Bool | { p.name == "Fantom" }
.map | Person p -> Str[] | { p.emails }
.flatten
.exclude | Str email -> Bool | { s.endsWith("gmail.com") }
.each { echo (it) }
// -> fantom@opera.org

Safety
● Null & Not-Null types
● Const classes and fields
● Guaranteed functions/closures with no mutations
(thread safe)
● Actor system (no shared state)
○ Unsafe wrapper - break your rules whenever you
want to save some time and shoot yourself into foot

Null and Not-Null types
● null assignment must be explicitly allowed in the code
● Default for types is not nullable version
● Automatic conversion
○ apparent bugs -> compile error
○ could work -> (maybe) runtime error

Null and Not-Null types (2)
class Nullable { // © Xored, Inc.
Void main() {
Int? nullable := null
Int nonNullable := 0
nonNullable = nullable // runtime err
nonNullable = null // compile err
do3(null) // compile err
do3(nullable) // runtime err
}
Int do1(Int? arg) { null } // compile err
Int do2(Int? arg) { arg } // runtime err
Int? do3(Int arg) { arg }
}

Const
● Const classes guarantee their internal state won't
change
● Const fields must be initialized on object construction
● Const fields must be const types or their values must be
converted by calling toImmutable for List, Map, Func

Const
class NonConst { // © Xored, Inc.
const Int constField
Int nonConstField
Void mutate() {
constField = 4 // compile err
nonConstField = 4 // ok
}
}
class Const {
new make(Int i, Str[] list) {
// implicit call of list.toImmutable
this.list = list
}
const Str[] list
}

Actor System
● Concurrency is not handled by thread but by Actors
● Actor is a const class extending concurrent::Actor
● Actors exchange immutable messages, i.e.
a. serialized content
b. constant content (allows to pass by reference)
● Actors typically contain private data, which are mutable
(thread local analogy)

// asynchronous incrementation of number send (blocking send operation)
actor:=Actor(ActorPool()) | Int msg -> Int | { msg + 1 }
5.times { echo(actor.send(it).get) }

Tooling and Build System
● Out-of-the-box build system using Fantom
○ handles standard setup with no additional code
○ easy to understand (simple implementation)
○ module dependencies and version checking
● Bundled simple testing framework fant
○ fits into default build structure
○ pretty standard lifecycle (junit like)
○ works also for javascript targeted code
using build
class Build : BuildPod {
new make() {
podName = "mongo"; summary = "Interface to MongoDB (http://www.mongodb.com)"
depends = ["sys 1.0", "inet 1.0", "concurrent 1.0"]
srcDirs = [`test/`, `fan/`, `fan/gridfs/`, `fan/bson/`]
docSrc = true } }

Modularity - Fantom repo & pods
// start all non-abstract MyService services in project CoolProj
using fanr
repo:=Repo.makeForUri(`http://my-fantom-repo/`)
pods:=repo.query(Str<|"*proj.name=="CoolProj"|>)
pods.each |pod|
{
echo("$p.name$p.version$p.depends")
pod.types.each |type|
{
if (type.fits(MyService#) && !type.isAbstract)
type.make->start
}
}

References
● Open source & docs
○ http://fantom.org/
○ http://www.talesframework.org/
○ http://www.fanzy.net/
○ http://langref.org/
○ http://rosettacode.org/wiki/Category:Fantom
● Commercial products
○ http://skyfoundry.com/skyspark/
○ http://www.xored.com/products/f4/
○ http://www.kloudo.com/
○ http://www.cull.io/

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