Expressions

Expressions are a fundamental concept in the Workflow language, used to represent and manipulate data. In essence, an expression is a combination of values, variables, operators, and functions that are processed to produce another value. For example, in a simple arithmetic expression like 3 + 4, the numbers 3 and 4 are combined using the + operator to produce the value 7.

Expressions can be as simple as a single value or variable, or as complex as a series of operations involving multiple functions and data types. They are essential for performing calculations, making decisions in code (through conditional expressions), and manipulating data.

Here are some examples of expressions:

Arithmetic expression

var sum = 10 + 15; //Adds 10 and 15

String concatenation

var greeting = "Hello, " + "world!"; // Concatenates two strings

Logical expression

var isAdult = age >= 18; // Evaluates to true if age is 18 or more

Function call

var area = math->pi() * math->pow(radius, 2); // Calculates area of a circle

Expressions consist of operands (values, variables, function calls) and operators (like +, -, *, /, and, or). The operands are the data items being manipulated, and the operators define how these items are processed.

The evaluation of expressions in the Workflow languages follows specific rules and order of operations, which determine how the individual components of an expression are processed to produce a final result.

Order of Operations

The Workflow language adheres to a predefined order of operations, similar to those in mathematics:

  1. Unary operators: Unary operators (like -, !) are applied first.
  2. Parentheses: Operations inside parentheses are performed next.
  3. Logical: or and and operators are evaluated next, form left to right.
  4. Equality: Equality (==, !=) then inequality (>, <, >=, <=) operations are performed next, form left to right.
  5. Multiplication and Division: These operations are performed next, from left to right.
  6. Addition and Subtraction: Finally, addition and subtraction are carried out, from left to right.

Associativity

When operators of the same precedence appear in an expression, associativity rules determine the order of evaluation. Binary operators are left-associative, meaning they are evaluated from left to right. For example, in the expression a - b - c, the subtraction is performed from left to right: (a - b) - c.

Operand Evaluation

Operands in an expression are evaluated as needed. Workflow language implements “short-circuit” evaluation meaning that some operands in logical expressions may not be evaluated at all if the result of the expression can be determined without them. For example, in the logical expression A and B, if A is false, B is not evaluated because the whole expression cannot be true.

Type Conversions

Some expressions involve operands of different types. In such cases, implicit or explicit type conversions may occur. Type conversions in expressions are done from left to right, this means that if the first operand of the expression is of a given type all of the remaining operands are converted to the first operand’s type. For example adding a string and a number will convert the number to string and the result will be a string concatenation.

Final Evaluation

After applying all these rules, the expression is evaluated to produce a single value. This value can be a number, a string, a boolean, or any other data type supported by the Workflow language.

In summary, the evaluation of an expression is a systematic process that follows the rules of precedence, associativity, and type conversions to derive a value from a combination of operators and operands.

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