variables.md

Variables and mutation

This tutorial requires the development stack. Published v0.0.1 does not support declarations. It shows how to name values, choose mutability, and keep earlier results when values change. The precise rules are in the variable reference.

Name a result

bind columns = 8;
bind rows = 5;
bind cells = columns * rows;
print(cells);

Output:

40

bind introduces a binding after its initializer. cells can use columns and rows because they are already declared. Names are case-sensitive ASCII identifiers; rows and Rows are different names.

By default, a binding is immutable. A declaration requires an initializer and a semicolon. There are no implicit declarations or uninitialized variables.

Change a value explicitly

var remaining = 10;
bind starting = remaining;
remaining -= 3;
remaining = remaining * 2;
print(starting);
print(remaining);

Output:

10
14

var permits assignment. The immutable starting keeps the value it copied; it is not an alias for the storage of remaining. Compound assignment supports +=, -=, *=, and /= and follows the checked integer rules in the value and operator reference.

This attempt to change an immutable binding fails with E0013:

bind remaining = 10;
remaining -= 3;

Use var only when later assignment is needed. The diagnostic also points to the declaration that established immutability.

Bind and replace strings

The string extension infers a binding's primitive type from its initializer:

var label = "Draft";
bind original = label;
print(label);
label = "Ready for review";
print(original);
print(label);

Output:

Draft
Draft
Ready for review

Reassignment replaces a string value without changing copies or earlier pending prints. A mutable binding must retain its inferred type. Changing label to an integer fails with E0015; string concatenation and string compound assignment are also unsupported.

Declare before use

This forward reference fails with E0010:

print(answer);
bind answer = 42;

Move the declaration before the print. Self-reference in an initializer also fails unless an outer binding with that name is already visible.

Use scarp check variables.srp to check syntax, names, mutability, primitive types, and arithmetic without printing. Every execution starts with fresh variable storage, including repeated executions of one compiled library program.

Next, use scopes and shadowing to reuse a name within a nested block.