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Source file src/cuelang.org/go/internal/core/adt/doc.go

Documentation: cuelang.org/go/internal/core/adt

     1  // Copyright 2020 CUE Authors
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // Package adt represents partially and fully evaluated CUE types.
    16  //
    17  // This package introduces several categories of types that indicate some set of
    18  // values that may be used in a certain situation. Concrete types may belong to
    19  // multiple categories.
    20  //
    21  // # Abstract Types
    22  //
    23  // The following types describe the a place where a value may be used:
    24  //
    25  //	Decl       a value than can be used as a StructLit element.
    26  //	Elem       a value than can be used as a ListLit element.
    27  //	Expr       represents an Expr in the CUE grammar.
    28  //	Value      a fully evaluated value that has no references (except for
    29  //	           children in composite values).
    30  //	Node       any of the above values.
    31  //
    32  // The following types categorize nodes by function:
    33  //
    34  //	Resolver   a reference to position in the result tree.
    35  //	Evaluator  evaluates to 1 value.
    36  //	Yielder    evaluates to 0 or more values.
    37  //	Validator  validates another value.
    38  //
    39  // # Reference resolution algorithm
    40  //
    41  // A Resolver is resolved within the context of an Environment. In CUE, a
    42  // reference is evaluated by substituting it with a copy of the value to which
    43  // it refers. If the copied value itself contains references we can distinguish
    44  // two different cases. References that refer to values within the copied
    45  // reference (not regarding selectors) will henceforth point to the copied node.
    46  // References that point to outside the referenced value will keep referring to
    47  // their original value.
    48  //
    49  //	a: b: {
    50  //	  c: int
    51  //	  d: c
    52  //	  e: f
    53  //	}
    54  //	f: 4
    55  //	g: a.b { // d.c points to inside the referred value, e.f, not.
    56  //	  c: 3
    57  //	}
    58  //
    59  // The implementation doesn't actually copy referred values, but rather resolves
    60  // references with the aid of an Environment. During compile time, each
    61  // references is associated with the label and a number indicating in which
    62  // parent scope (offset from the current) this label needs to be looked up. An
    63  // Environment keeps track of the point at which a value was referenced,
    64  // providing enough information to look up the labeled value. This Environment
    65  // is the identical for all references within a fields conjunct. Often, an
    66  // Environment can even be shared among conjuncts.
    67  //
    68  // # Values
    69  //
    70  // Values are fully evaluated expressions. As this means that all references
    71  // will have been eliminated, Values are fully defined without the need for an
    72  // Environment. Additionally, Values represent a fully evaluated form, stripped
    73  // of any comprehensions, optional fields or embeddings.
    74  package adt
    75  

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