Expression Syntax

Expresso provides a simple yet powerful syntax for writing expressions. This page covers all the syntax elements available in the language.

Literals

Expresso supports various types of literals:

// String literals
"Hello, World!"
'Hello, World!'

// Number literals
42
3.14
-42
-3.14

// Boolean literals
true
false

// Null literal
null

Variables

Variables are accessed using the $ prefix:

// Simple variable
$name

// Object property access
$person.name
$person.address.city

// Array access
$scores[0]
$items[1].name

// Null-safe property access
$person?.name
$person?.address?.city

// Null-safe array access
$person?.hobbies?[0]

// Null coalescing operator (default value)
$person?.name ?? 'Unknown'
$person?.address?.city ?? 'No City'
$person?.hobbies?[0] ?? 'No Hobby'

Null Safety Operators

Expresso provides special operators for handling null values safely:

// Null-safe property access (?.)
// Returns null if person is null instead of throwing an exception
$person?.name

// Null-safe chained property access
// Returns null if any part of the chain is null
$person?.address?.city

// Null-safe array access (?[])
// Returns null if the array/list is null or the index is out of bounds
$person?.hobbies?[0]

// Null coalescing operator (??)
// Provides a default value if the left expression evaluates to null
$person?.name ?? 'Unknown'
$person?.address?.city ?? 'No City'
$scores?[5] ?? 0

These operators help you write more concise and robust code by eliminating the need for explicit null checks.

Operators

Expresso supports various operators:

// Arithmetic operators
$x + $y
$x - $y
$x * $y
$x / $y
$x % $y

// Comparison operators
$x > $y    // Greater than
$x < $y    // Less than
$x >= $y   // Greater than or equal to
$x <= $y   // Less than or equal to
$x == $y   // Equality
$x != $y   // Inequality

// Logical operators
$condition1 && $condition2  // Logical AND
$condition1 || $condition2  // Logical OR
!$condition  // Logical NOT

Comparison operators work with numbers, strings, and dates:

// Numeric comparisons
10 > 5                      // true
5 < 10                      // true
5 >= 5                      // true
5 <= 5                      // true

// String comparisons (lexicographic ordering)
'banana' > 'apple'          // true
'apple' < 'banana'          // true
'banana' >= 'banana'        // true
'apple' <= 'banana'         // true

In logical operations, Expresso follows "truthiness" rules similar to JavaScript:

• null values are falsy (treated as false in logical expressions)
• Boolean values behave as expected (true is truthy, false is falsy)
• All other non-null values (numbers, strings, objects, arrays) are truthy

This allows for concise null checking and logical expressions:

// These evaluate to true
!null
true || null
null || true
!null && true
"hello" && true     // Non-null non-boolean values are truthy
42 || false         // Numbers are truthy

// These evaluate to false
null && true
true && null
null && null
null || false
false && "hello"    // Short-circuit makes this false

Type Handling in Comparisons

When comparing values of different types, Expresso follows these rules:

// Number comparison - types are normalized for numeric comparisons
5 == 5.0                   // true
5 != 5.0                   // false
10 > 5.0                   // true

// String equality - type matters
5 == "5"                   // false (different types)
5 != "5"                   // true (different types)

// Null comparisons
$value == null             // true if $value is null
$value != null             // true if $value is not null

// Equality in comparisons with null
null == null               // true
"hello" == null            // false
null != "hello"            // true

// Ordering comparisons with null always return false
null > 5                   // false
5 > null                   // false
null < 5                   // false
5 < null                   // false

Function Calls

Functions are called using parentheses:

// Built-in functions
length($string)
substring($string, 0, 5)
round($number, 2)
max($x, $y)

// Function with multiple arguments
concat($first, $second, $third)

Operator Precedence

Expresso follows standard operator precedence rules:

1. Parentheses ()
2. Function calls func()
3. Member access ., Array access [], Null-safe access ?., Null-safe array access ?[]
4. Unary operators !, -
5. Multiplicative operators *, /, %
6. Additive operators +, -
7. Relational operators >, <, >=, <=
8. Equality operators ==, !=
9. Logical AND &&
10. Logical OR ||
11. Null coalescing operator ??