Getting Started

The Philosophy of Visual Lambda

• Visualized Programming
  Programming with Visual Lambda is done primarily with mouse. The program is visualized with a tree structure.
• Context Sensitive Programming
  The Visual Lambda editor GUI application guides user throughout the entire programming process by providing user all possible choices they can take in the next step.
• Domain Specific Programming
  Visual Lambda limits all possible actions user can use in a specific application domain. By limiting the application domain user can build safer and clear applications without sacrificing flexibility mathematically.

Expression

An expression in a programming language is a combination of values, variables, operators, and functions that are interpreted (evaluated) according to the particular rules of precedence and of association for a particular programming language, which computes and then produces (returns, in a stateful environment) another value.

The goal of Visual Programming is to build "modules" with specific "signature". For more information about module and signature, see "Type, Module and Signature".

Expressions usually take several operands. For example, "addition expression" takes two or more operands to calculate the sum of them. The oprands can be other expressions as long as the data type matches.

A Visual Lambda module is an expressions itself.

Below are types of expressions currently supported in Visual Lambda:

Note: Users can just try to comprehend as much as possible and then proceed to the following chapters. Users can always go back and reference the expression types in the list in the future.

• [Built in] Math Expressions
  The Built in math expressions are basic algebraic operators, logical operatorsand comparison operators.
  There are two types of algebraic operations in this category, arithmetic and bitwise operations.
  Arithmetic operators are used to perform many of the familiar arithmetic operations that involve the calculation of numeric values. Arithmetic operators include Addition (+); Subtraction (-); Multiplication (*); Division (/); Modulo operation (%).
  Bitwise operators evaluating two values in binary (base 2) form. Bitwise operations include And (&); Or (|); Not (~); Xor (^).
  Logical operators compare Boolean values and return a Boolean result. Logical operations include And (&&); Or (||); Not (!); Xor (^).
  Comparison operators compare two expressions and return a Boolean value that represents the result of the comparison. Comparison operations include Equality (==); Inequality (!=); Less than (<); Greater than (>); Less than or equal to (<=); Greater than or equal to (>=)
• [Built in] String Functions
  String functions are operations that involve a text string. Below are some examples of string functions.
  Properties: such as Length
  Comparison: such as Compare, StartsWith, EndsWith
  Search: such as IndexOf, LastIndexOf
  Transform: such as Insert, PadLeft, PadRight, Remove, Replace, Substring, ToLower, ToUpper, Trim
• [Built in] Char Functions
  String functions are operations that involve a character. Below are some examples of character functions.
  Test: IsControl, IsDigit, IsLetter, IsUpper, IsLower, IsNumber, IsPunctuation, IsSeparator, IsSymbol IsWhiteSpace, etc.
  Conversion: ToUpper, ToLower
• [Built in] DateTime Functions
  Built in DateTime functions are functions operate on a Datetime type. Below are some examples of DateTime functions.
  Comparison: Compare
  Component Access: get_Year, get_Month, get_Day, get_Hour, get_Minute, get_Second, get_TimeOfDay etc
  System Time: get_Now, get_UtcNow, get_Today
  Calculation: Add, Substract, AddYears, AddMonths, AddDays, AddHours, AddMinutes, AddSeconds, AddMilliSeconds, DaysInMonth, IsLeapYear
  Transform: ToLocalTime, ToUniversalTime
  Constructor: CreateDateTime
• [Built in] Time Functions
  Built in DateTime functions are functions operate on a timeonly type. Below are some examples of time functions.
  Comparison: Compare
  Component Access: get_Days, get_Hours, get_Minutes, get_Seconds, etc
  Calculation: Add, Substract, Negate
  Constructor: FromDays, FromHours, FromMinutes, FromSeconds, FromMilliseconds, CreateTime
• [Built in] Conversion
  Built in conversion provides the conversion among types. For example, all primitive types can be converted to and from a string type.
  Integers can be converted into float values but not vice versa.
• [Built in] Collection Functions
  Built in DateTime functions are functions operate on a collection type. Below are some examples of collection functions.
  Properties: get_Length
  Access: get_Item
  Search: Contains, FirstIndexOf
• [System] Math
  The system math functions contain trigonometric, logarithmic, and other common mathematical functions. Below are some examples of system math functions:
  Trigonometric: Sin, Sinh, Cos, Cosh, Tan, Tanh, Asin, Atan, Atan2
  Logarithmic: Log, Log10
  Other: Abs, Ceiling, Floor, Exp, Pow, Max, Min, Round, Sign, Truncate
• FIX Message Operations
  FIX message operations are functions operate on a FIX message or repeating group instance.
  Properties: getMsgType
  Access: GetIntValue, GetBooleanValue, GetStringValue, GetCharValue, SetValue
• Value
  Values are constants.
• Template
  Template is a special type of constant. The constant value of template can be customized during deployment. It's a powerful feature of Visual Lambda. We will explain more details about template in the following chapters.
• [FIX] FieldTags
  FIX field tag is a special constant integer value type. User can indirectly specify the value of the expression by choosing a tag name.
• [FIX] MessageTypes
  FIX message type is a special constant string value type. User can indirectly specify the value of the expression by choosing a message name.
• [FIX] ValidValues
  FIX field valid value is a special constant value type. User can indirectly specify the value of the expression by choosing a pair of field name and valid value name.

Decision

Decision is a special type of expression. It can be composed of two expressions. The first expression has a type of "Boolean" value (in Visual Lambda we call it "Condition"). The second one does not have a return value (in Visual Lambda we call that kind of expression an "Action"). The "Action" can only be executed if the evaluation of "Condition" returns "true".

Expression Tree and Decision Tree

Both expressions and decisions can be expressed as a tree. Visual Lambda editor helps user to build the expression and decision trees.

For example, the expressing is display as a tree view with the operands as the child nodes. An operand can be another expression, too. So expressions can be nested to form an express tree. Remember, the Visual Lambda module is an expression, too.

In the following chapters we will walk through building the expression trees fro Visual Lambda modules.