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diff --git a/spec/scope.md b/spec/scope.md index e1288cdb..b25c0ce0 100644 --- a/spec/scope.md +++ b/spec/scope.md @@ -28,14 +28,16 @@ The six special names are `𝕨𝕩𝕗𝕘𝕤𝕣`, and the tokens `𝕎𝕏 ### Imports and exports -The names to be used in an `IMPORT`, that is, `LHS_NAME` terms in an `NS_VAR` or `nsLHS`, are variable references inside that `IMPORT`'s `brNS` term. If they appear without an accompanying `lhs "⇐"` term (in `NS_VAR`), then this is in addition to their role as identifiers within the actual enclosing scope, which works like any other assignment. These references behave as though they are at the end of the `brNS` term, that is, they "see" all definitions in the block. However, they must refer to identifiers that are *exported* by that block; references to any other variable cause an error much like references that have no definition. +Names that are preceded by an `atom "."` term, or that appear as `LHS_NAME` terms in an `NS_VAR` or `lhsNs`, are variable references in a namespace: in the first case, the result of the `atom` node, and in the second, of the overall assignments `subExpr` right hand side. These names do not follow lexical scoping; in general they must be stored in order to perform a name lookup when the namespace is available. Such a name in `lhsNs`, or in `NS_VAR` with no accompanying `lhs "⇐"` term, additionally serves as an identifier within the actual enclosing scope, which works like any other assignment. -An identifier is exported if the `ASGN` node in its definition is `"⇐"`, or if it appears anywhere in an `EXPORT` term. An identifier can only be exported in the scope where it is defined, and not in a containing scope. An `EXPORT` term that includes an identifier from such a scope causes an error. +An identifier is *exported* if the `ASGN` node in its definition is `"⇐"`, or if it appears anywhere in an `EXPORT` term. An identifier can only be exported in the scope where it is defined, and not in a containing scope. An `EXPORT` term that includes an identifier from such a scope causes an error. ## Variables A *variable* is an entity that permits two operations: it can be *set* to a particular value, and its *value* can be obtained, resulting in the last value it was set to. When either operation is performed it is referred to as *accessing* the variable. -When a body in a block is evaluated, a variable is created for each definition (that is, defined identifier instance) the body contains. Whenever another block—the block itself, not its contents—is evaluated during the execution of the block, it is linked to the currently-evaluating block, so that it will use the variables defined in this instance. By following these links repeatedly, an instance of a block is always linked to exactly one instance of each block that contains it. These links form a tree that is not necessarily related to the call stack of functions and modifiers. Using the links, the variable an identifier refers to is the one corresponding to that variable's definition in the linked instance of the containing scope for the definition. +When a body in a block is evaluated, it creates a *namespace*, which contains a variable for each definition (that is, defined identifier instance) the body contains. Whenever another block—the block itself, not its contents—is evaluated during the execution of the block, it is linked to the currently-evaluating block, so that it will use the variables defined in this instance. By following these links repeatedly, an instance of a block is always linked to exactly one instance of each block that contains it. These links form a tree that is not necessarily related to the call stack of functions and modifiers. Using the links, the variable an identifier refers to is the one corresponding to that variable's definition in the linked instance of the containing scope for the definition. The first access to a variable must be made by its definition (this also means it sets the variable). If a different instance of its identifier accesses it first, then an error results. This can happen because every scope contained in a particular scope sees all the definitions it uses, and such a scope could be called before the definition is run. Because of conditional execution, this property must be checked at run time in general; however, in cases where it is possible to statically determine that a program will always violate it, a BQN instance can give an error at compile time rather than run time. + +A namespace defines a mapping from names to variables: if the given name is shared by an exported identifier in the body used to create that namespace, then that name maps to the variable corresponding to that identifier. The mapping is undefined for other names. |