Expressions and Statements

Bliss draws a strict distinction between expressions and statements. This distinction is not a convention — it is enforced by the language.

Expressions

An expression is any construct that produces a value. Expressions can be used anywhere a value is expected — as an initializer, as a function argument, or as a condition.

The following are expressions in Bliss:

Literals — a direct value written in source code.

21
true
"Hello"
'x'

Identifiers — a named value.

x
age
isReady

Binary expressions — two expressions combined with an operator, producing a value.

x + 5
age >= 18
a && b

Unary expressions — a single expression preceded by an operator.

!isReady
-x

Function calls — always an expression in Bliss, regardless of whether the function returns a meaningful value or void.

add(3, 5)
greet("Alice")

Data initialization — a data type paired with a field initializer block. The block here is part of the expression, not a standalone construct.

User { name = "Alice", age = 21 }

Statements

A statement is any construct that performs an action but produces no value. Statements cannot be used where a value is expected.

The following are statements in Bliss:

Variable declaration — declares a variable and optionally binds it to an expression.

let x: i32 = 5;
let name: u8[];

Reassignment — binds a new expression to an existing variable.

x = x + 1;
arr[0] = 10;

Function definition — defines a named function.

fx add(x: i32, y: i32) -> i32 {

}

Control flow — if, elif, else, and while are all statements.

if ( x > 0 ) {

}

while ( isRunning ) {

}

Blocks — a { } block is a statement. It is structural and produces no value on its own. The only context where a block appears as part of an expression is data initialization.

import and use — bring external packages and internal files into scope.

import std;
use src.utils;

The Distinction in Practice

Because assignment is a statement and not an expression, constructs like the following are not valid in Bliss:

let x: i32 = let y: i32 = 5;  // ❌ declaration is not an expression
while ( x = 5 ) { }           // ❌ assignment is not an expression

A function call, however, is always an expression and can appear as a standalone statement by itself:

greet("Alice");   // valid — expression used as a statement