Variables and scopes

In v0.0.5-alpha.1, Scarp uses bind for immutable values and var for mutable values. Earlier prereleases used different declaration syntax; see compatibility.

New since published alpha.2: Optional checked annotations such as bind count: integer = 42; are covered in the verified typed-bindings and conversions lesson. This page's examples and original implementation references remain pinned to alpha.1; do not infer that alpha.1 accepts declaration annotations.

Immutable bindings

bind width = 6;
bind height = 7;
bind area = width * height;
print(area); // 42

Bindings must have a name, =, an initializer, and a trailing semicolon. The value's type is inferred. There are no uninitialized declarations or implicit new variables. A name becomes visible after its initializer; self-references, forward references, and duplicates in one scope are errors.

Mutable bindings

var count = 2;
bind snapshot = count;
count += 5;
print(count);    // 7
print(snapshot); // 2

A mutable value may be changed with =, +=, -=, *=, and /=. Compound operations require numeric values of the same type. A reassignment must preserve the original inferred type. Reassigning a copy does not change the original snapshot.

Lexical scopes and shadowing

var total = 1;
{
    bind total = total + 10;
    print(total); // 11
}
total += 2;
print(total); // 3

The initializer in the inner block reads the outer total, then introduces a new one that hides it. On block exit the inner name goes out of scope. Assignment resolves the nearest visible binding; it cannot skip an immutable inner binding to mutate an outer one.

Restrictions

File and function scopes are distinct. Functions cannot implicitly capture arbitrary top-level script variables. Blocks are statements, not expressions. There is no string concatenation via +, implicit conversion, increment operator, or assignment expression. See memory and lifetimes for how scope retirement works internally.

Verified against: variable reference, mutability tests.