| // Copyright 2020 CUE Authors |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| // Package adt represents partially and fully evaluated CUE types. |
| // |
| // This package introduces several categories of types that indicate some set of |
| // values that may be used in a certain situation. Concrete types may belong to |
| // multiple categories. |
| // |
| // |
| // Abstract Types |
| // |
| // The following types describe the a place where a value may be used: |
| // |
| // Decl a value than can be used as a StructLit element. |
| // Elem a value than can be used as a ListLit element. |
| // Expr represents an Expr in the CUE grammar. |
| // Value a fully evaluated value that has no references (except for |
| // children in composite values). |
| // Node any of the above values. |
| // |
| // The following types categorize nodes by function: |
| // |
| // Resolver a reference to position in the result tree. |
| // Evaluator evaluates to 1 value. |
| // Yielder evaluates to 0 or more values. |
| // Validator validates another value. |
| // |
| // |
| // Reference resolution algorithm |
| // |
| // A Resolver is resolved within the context of an Environment. In CUE, a |
| // reference is evaluated by substituting it with a copy of the value to which |
| // it refers. If the copied value itself contains references we can distinguish |
| // two different cases. References that refer to values within the copied |
| // reference (not regarding selectors) will henceforth point to the copied node. |
| // References that point to outside the referened value will keep referring to |
| // their original value. |
| // |
| // a: b: { |
| // c: int |
| // d: c |
| // e: f |
| // } |
| // f: 4 |
| // g: a.b { // d.c points to inside the referred value, e.f, not. |
| // c: 3 |
| // } |
| // |
| // The implementation doesn't actually copy referred values, but rather resolves |
| // references with the aid of an Environment. During compile time, each |
| // references is associated with the label and a number indicating in which |
| // parent scope (offset from the current) this label needs to be looked up. An |
| // Environment keeps track of the point at which a value was referenced, |
| // providing enough information to look up the labeled value. This Environment |
| // is the identical for all references within a fields conjunct. Often, an |
| // Environment can even be shared among conjuncts. |
| // |
| // |
| // Values |
| // |
| // Values are fully evaluated expressions. As this means that all references |
| // will have been eliminated, Values are fully defined without the need for an |
| // Environment. Additionally, Values represent a fully evaluated form, stripped |
| // of any comprehensions, optional fields or embeddings. |
| // |
| package adt |
