This page assumes you have some experience in Programming and App Inventor.

Note to AI

• Falcon syntax was created for App Inventor that follows 1-based indexing.
• List, and Dictionaries are passed as references, only text and number are copied.
• Tags of various languages are used only for syntax highlighting

Data types

• Text
  • "Hello, World!"
• Boolean
  • true and false
• Number
  • 123, 3.14
• List
  • [1, 2, 3, 4, ...]
• Dictionary
  • {"Animal": "Royal Bengal Tiger", "country": "India"}

Operators

• Arithmetic operators
  • +, -, *, /, ^ (power)
• Logical operators
  • || , &&,
• Bit-wise operators
  • |,&, ~ (xor)
• Equality operators
  • ==, !=
• Relational operators
  • <, <=, >, >=
• Text comparison operators
  • === (text equals)
  • !== (text not equals)
  • << (text less than)
  • >> (text greater than)
• Unary operators
  • ! (not)
• Text join operator _
  • e.g. "Hello " + "World!"
• Pair operator
  • e.g. "Fruit" : "Melon"
• Question operator (?)
  • Check if a value is of a certain type
    • e.g. x ? text, or number, or list or dict
  • Is of a number type
    • e.g. "123" ? number, or base10, hexa, bin
  • Check for a empty text or a list
    • e.g. namesList ? emptyList or "hello" ? emptyText"

Operator precedence

Precedence of operators dictates which operation is prioritized. (* and / parsed before + and -)

In Falcon, it is similar to that of Java. Below is the list, ranked from the lowest priority to the highest.

1. AssignmentType (=)
2. Pair (:)
3. TextJoin (_)
4. LLogicOr (||)
5. LLogicAnd (&&)
6. BBitwiseOr (|)
7. BBitwiseAnd (&)
8. BBitwiseXor (~)
9. Equality (==, !=, ===, and !==)
10. Relational (<, <=, >, >=, <<, and >>)
11. Binary (+ and -)
12. BinaryL1 (* and `)
13. BinaryL2 (^)

Variables

A global variable:

global name = "Kumaraswamy"

# access global var
println(this.name)

A simple local variable:

local age = 12

# accessing local var
println(age)

A local variable statement with a scoped body:

local (
  x = 8,
  j = 2,
  k = 12
) {
   # use x, j, k here
}

A returning variable expression:

compute(a = 2, b = 8) -> a * b

Conditions and loops

If statement

local age = 8

if age < 18 {
  println("You are a kid :D")
} elif age == 18 {
  println("Congrats! You are an adult!")
} else {
  println("Hola, grown person!")
}

Returning if-else expression

Ternary like expression for returning values. Unlike If statement, use () between your condition.

local(a = 8, b = 2) {
  println("Maximum " _ if (a > b) a else b)
}

For loops

while statement to iterate till the condition is true.

local x = 0

while true {
  x = x + 1
  if x == 5 {
    break
  }  
}

for statement for index based iteration:

for x: 1 to 10 by 2 {
  println(x)
}

each statement is used to iterate over a list:

local countries = ["India", "Japan", "Russia", "Germany"]

each name -> countries {
  println(name)
}

or a dictionary:

local personality = { 
  "food": "Masala Dosa",
  "fruit": "Mango",
  "animal": "The Royal Bengal Tiger"
}

each key::value -> personality {
   println("My favourite " _ key _ " is " _ value)
}

Do expression

do expression is to execute a body and return a result.

do {
  ...
} -> result # outer scope

The result expression in do, is executed outside the body (outer scope).

Colors

color:color_name returns int of a specified color.

white, black, red, pink, orange, yellow, green, cyan, blue, magenta, lightGray, gray, darkGray are the supported color types.

Functions

A void function:

func funcName(x, y, z) {
  ...
}

A returning function:

func greet(name) = "Hello " _ name _ "!"

Functions

Math

• dec(string), bin(string), octal(string), hexa(string) parses string from respective base. The string provided must be a static constant i.e. no variables or function calls.

• root(number)

• abs(number)

• neg(number)

• log(number)

• exp(number)

• round(number)

• ceil(number)

• floor(number)

• sin(number)

• cos(number)

• tan(number)

• asin(number)

• acos(number)

• atan(number)

• degrees(number)

• radians(number)

• decToHex(number)

• decToBin(number)

• hexToDec(number)

• binToDec(number)

• randInt(from, to)

• randFloat()

• setRandSeed(number) sets the random generator seed

• min(...) and max(...)

• avgOf(list), maxOf(list), minOf(list), geoMeanOf(), stdDevOf(), stdErrOf()

• modeOf(list)

• mod(x, y), rem(x, y), quot(x, y) for modulus, remainder and quotient

• atan2(a, b)

• formatDecimal(number, places)

Control

• println(any)
• openScreen(name) opens an App Inventor screen
• openScreenWithValue() opens App Inventor screen with a value
• closeScreenWithValue() closes the screen with a val
• getStartValue() returns start value of the App
• closeSceen() closes current App Inventor screen
• closeApp() closes the Android App
• getPlainStartText() returns plain start text of the App

Values

• copyList(list)
• copyDict(dict)
• makeColor(rgb list)
• splitColor(number)

Generic calls

• set(comonent_group, instance_name, property_name, value) generic property set call
  e.g. set(Button, Button1, Text, "Hello, World")
  

  The first three arguments must be call time constants, no expressions or variables allowed

• get(component_group, instance_name, property_name) generic property get call
  e.g. get(Button, Button1, Text)
  
  

• call(component_group, instance_name, method_name) generic method call
  e.g. call(Notifier, Notifier1, ShowAlert, "Hello, World")
  
  

• every(component_type) returns a list of all component instances belonging to that type
  e.g. every(Button)

Methods

e.g. "Hello ".trim()

Text

• textLen()
• trim()
• uppercase()
• lowercase()
• startsWith(piece)
• contains(piece)
• containsAny(word list)
• containsAll(word list)
• split(at)
• splitAtFirst(at)
• splitAtAny(word list)
• splitAtFirstOfAny(word list)
• splitAtSpaces()
• reverse()
• csvRowToList()
• csvTableToList()
• segment(from number, length number)
• replace(target, replacement)
• replaceFrom(map dictionary)
• replaceFromLongestFirst(map dictionary)

List

• listLen()
• add(any...)
• containsItem(any)
• indexOf(any)
• insert(at_index, any)
• remove(at_index)
• appendList(another list)
• lookupInPairs(key, notfound)
• join(text separator)
• slice(index1, index2)
• random()
• reverseList()
• toCsvRow()
• toCsvTable()
• sort()
• allButFirst()
• allButLast()
• pairsToDict()

Dictionary

• dictLen()
• get(key)
• set(key, value)
• delete(key)
• getAtPath(path_list, notfound)
• setAtPath(path_list, value)
• containsKey(key)
• mergeInto(another_dict)
• walkTree(path)
• keys()
• values()
• toPairs()

List access

local numbers = [1, 2, 4]

# access second element (1 based indexing)
println(numbers[2])

# change the first element
numbers[1] = 8

Dictionary access

local(personality = {
  "food": "Masala Dosa",
  "fruit": "Mango",
  "animal": "The Royal Bengal Tiger"
}) {
    println(personality.get("food", 0))
}

List transformer

Style inspired from Kotlin, falcon has list transformers (aka lambdas).

Let's say I have a list of number of lemons sold each day for a week. Although some days were missed and were marked N/A.

global LemonadeSold = [9, 12, "N/A", 15, 18, "N/A", 8]

Now I got to calculate the revenue of the week, knowing that each lemon costs two dollars.

This can be done by using list transformers/lambdas.

global LemonadeSold = [9, 12, "N/A", 15, 18, "N/A", 8]

func GetTotalRevenue() = 
  this.LemonadeSold
     .filter { n -> n ? number}
     .map { n -> n * 2}
     .reduce(0) { x, soFar -> x + soFar }

println("Weekly revenue selling lemons was " _ GetTotalRevenue())

These are available list transformers:

• map { x -> expr } maps each element of the list to a new value
• filter { x -> bool_expr } filters out unwanted elements from a list
• sort { m, n -> bool_m_preceeds_n_expr } helps to define a custom sort
• sortByKey { n -> key_of_n } sorts the list by first calling key function
• min { m, n -> bool_m_preceeds_n_expr } returns minimum of a list
• max { m, n -> bool_m_preceeds_n_expr } returns maximum of a list
• reduce(initValue) { x, valueSoFar -> new_value_expr } helps to reduce values of a list to a single value

Helper Blocks

By default, any asset helper block is mapped to a equivalent text block.

For enums: key@option
e.g. FileScope@App

Component access

Property Get/Set

println(Button1.Text) # get and print Button1' text

# change Button1's text to "Hello, World!"
Button1.Text = "Hello, World!"

Method calls

# Show a toast for "Hello World"
Notifier1.ShowAlert("Hello, World!")

Events

You do not need to explicitly define parameters.

when Button1.Click {
  # do something
}

for a generic event:

when any Button.Click {
  # do something
}