Programs and let variables

A program is a sequence of instructions that Sugar runs from top to bottom. A Sugar text block can contain a small program:

text {
  let basePower = 8;
  let bonus = 3;
  let totalPower = basePower + bonus;
  "@1 attacks with {totalPower} power."
}

Sugar creates basePower, then bonus, then totalPower. The final string becomes the message.

Statements and final expressions

A statement is an instruction performed by a program. These three declarations are statements:

let basePower = 8;
let bonus = 3;
let totalPower = basePower + bonus;

Each ends with ;. A line break is only spacing; it does not finish a statement.

The last line of a value-producing block is different:

"@1 attacks with {totalPower} power."

It has no semicolon because it is the block’s final expression. Its value becomes the value produced by the entire block.

Declare a temporary variable

let creates a variable that exists only while the current program runs:

let totalPower = basePower + bonus;

The declaration has the same basic shape as var: a keyword, a name, =, an initial value, and a semicolon. Its lifetime is different. A let variable disappears when its surrounding program finishes.

Use let for an intermediate result that does not belong to the creation’s lasting state:

text {
  let subtotal = price * quantity;
  let finalPrice = subtotal - discount;
  "The final price is {finalPrice}."
}

Scope inside a block

A variable name is available only inside the region where it is declared. This region is its scope.

text {
  let greeting = "Welcome back";
  "{greeting}, @1!"
}

greeting exists from its declaration to the end of this text block. Code outside the block cannot read it.

Top-level var declarations have a wider scope: every text, function, and Item action in the same Code module can use them.

The next lesson changes mutable variables with assignment statements.