Skip to main content

Flex Syntax Overview

Example Flex File

module ExamplePackage.ExampleModule
// This is a comment
/* This is a block comment
that ends on another line */
const pi : float64 = 3.14;
struct StructA {
a : int32;
b : bit;
struct StructB extends StructA {
c : int32;
variant VariantA {
Complex(int8, float32);
enum color int32 {
Red = 1;
Green = 2;
Yellow = 3;
Blue = 4;
function square(i : int32) -> int32 {
i * i;

General Tips

  • Flex is case-sensitive.
  • Declared names may contain letters a-z,A-Z , numbers 0-9 , and underscores _. They must begin with a letter or an underscore.
  • An object's data type is declared after its name, separated by a colon. NAME : TYPE
  • Functions must have a return data type defined. function NAME( PARAMETERS ) -> RETURN TYPE { BODY; }
  • End of lines are specified using a semicolon. ;


  • // Single line comment
  • /* */ Multi line comment


  • bit Single bit (true or false)
  • intN N bit two's complement signed integer. May be int8, int16, int32, or int64
  • uintN N bit unsigned integer. May be uint8, uint16, uint32, or uint64
  • floatN N bit IEEE 754 floating point number. May be float32 or float64
  • string Encoding independent string
  • T[] An array of indeterminate length of things of type T
  • T[N] An array of N things of type T
  • T[N..M] An array of anywhere from N to M things of type T
  • (T0, T1, ..., TN) A tuple with element types T0 .. TN
  • Optional<T> An optional type T - may either contain a T or nothing
  • Stream<T> An infinite stream of objects of type T


  • const Declare a constant object of a given type
  • struct Declare a structured type object containing fields that each have an explicitly declared type
  • message Declare a message type object that can be used as a Message in Tangram ProTM, and used as input and output for a transform
  • variant Declare a variant type object containing fields that may not have an explicitly declared type
  • enum Declare an enumerated type object containing fields and values that all share the same type
  • newtype Declare a new type object containing a single field
  • function Declare a function
  • transform Declare a transform function that can be used as a Transform in Tangram ProTM
  • let Declare a variable within the scope of a function or transform


  • Arithmetic: +, -, /, *, % Defined for numeric types
  • Comparison: <, >, <=, >= Defined for numeric types
  • Equality: ==, != Defined for almost all types
  • Boolean: &&, ||, ! Defined for bit
  • Bitwise: &, |, ~, ^ Defined for bit, bit[], int, uint


  • Bit literals are true and false
  • String literals are delimited by double quotes. "This is a string"
  • Floating literals contain a decimal point. 1.618 and 0.05 are valid, whereas 1. and .05 are invalid
  • Array literals are delimited with square brackets. [1,2,3] : int32[]
  • Tuple literals are delimited with parentheses. (1,false,"foo") : (int32,bit,string)
  • Hexadecimal literals begin with 0x
  • Binary literals begin with 0b
  • Zero can be represented as 0 in intN and uintN, and represented as 0.0 in float32 and float64
  • Underscores _ can be used in numeric literals as digit separators. 1_000_000 is equivalent to 1000000