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sass/spec/variables.md
Natalie Weizenbaum 353942622f Move and restructure how we specify scopes
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Variables

Table of Contents

Syntax

Variable            ::= PlainVariable | NamespacedVariable
PlainVariable       ::= '$' <ident-token>
NamespacedVariable  ::= <ident-token> '.$' PublicIdentifier
VariableDeclaration ::= Variable ':' Expression ('!global' | '!default')*

No whitespace is allowed after the $ in PlainVariable or before or after the .$ in NamespacedVariable. Each of !global and !default is allowed at most once in VariableDeclaration. As with all statements, a VariableDeclaration must be separated from other statements with a semicolon.

Semantics

Executing a Variable Declaration

To execute a VariableDeclaration declaration:

  • Let value be the result of evaluating declaration's Expression.

  • Let name be declaration's Variable.

  • Let resolved be the result of resolving a variable named name.

  • If name is a NamespacedVariable and declaration has a !global flag, throw an error.

  • Otherwise, if resolved is a variable from a built-in module, throw an error.

  • Otherwise, if declaration is outside of any block of statements, or declaration has a !global flag, or name is a NamespacedVariable:

    • If declaration has a !default flag, resolved isn't null, and resolved's value isn't null, do nothing.

    • Otherwise, if resolved is a variable in another module:

      • Evaluate declaration's value and set resolved's value to the result.

    • Otherwise:

      • If declaration is outside of any block of statements, it has a !default flag, and config contains a variable named name whose value is not null:

        • Let value be the value of config's variable named name.

      • Otherwise, let value be the result of evaluating declaration's value.

      • If name doesn't begin with - or _, add a variable with name name and value value to module.

        This overrides the previous definition, if one exists.

      • Add a variable with name name and value value to import.

        This also overrides the previous definition.

  • Otherwise, if declaration is within one or more blocks associated with @if, @each, @for, and/or @while rules and no other blocks:

    • If resolved is not null:

      • If declaration has a !default flag and resolved's value isn't null, do nothing.

      • Otherwise, let value be the result of evaluating declaration's value.

      • If name doesn't begin with - or _, add a variable with name name and value value to module.

        This overrides the previous definition, if one exists.

      • Add a variable with name name and value value to import.

        This also overrides the previous definition.

  • Otherwise, if resolved is null, set the current scope's variable name to value.

  • Otherwise, set resolved's value to value.

Evaluating a Variable

To evaluate a Variable variable:

  • Let definition be the result of resolving a variable named variable. If this returns null, throw an error.

  • Return definition's value.