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// Copyright 2014 The Bazel Authors. All rights reserved.
//
// 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 com.google.devtools.build.lib.syntax;
import java.io.IOException;
/**
* Base class for all expression nodes in the AST.
*/
public abstract class Expression extends ASTNode {
/**
* Kind of the expression. This is similar to using instanceof, except that it's more efficient
* and can be used in a switch/case.
*/
public enum Kind {
BINARY_OPERATOR,
COMPREHENSION,
CONDITIONAL,
DICTIONARY_LITERAL,
DOT,
FUNCALL,
IDENTIFIER,
INDEX,
INTEGER_LITERAL,
LIST_LITERAL,
SLICE,
STRING_LITERAL,
UNARY_OPERATOR,
}
/**
* Returns the result of evaluating this build-language expression in the
* specified environment. All BUILD language datatypes are mapped onto the
* corresponding Java types as follows:
*
* <pre>
* int -> Integer
* float -> Double (currently not generated by the grammar)
* str -> String
* [...] -> List<Object> (mutable)
* (...) -> List<Object> (immutable)
* {...} -> Map<Object, Object>
* func -> Function
* </pre>
*
* @return the result of evaluting the expression: a Java object corresponding
* to a datatype in the BUILD language.
* @throws EvalException if the expression could not be evaluated.
* @throws InterruptedException may be thrown in a sub class.
*/
public final Object eval(Environment env) throws EvalException, InterruptedException {
try {
if (Callstack.enabled) {
Callstack.push(this);
}
try {
return doEval(env);
} catch (EvalException ex) {
throw maybeTransformException(ex);
}
} finally {
if (Callstack.enabled) {
Callstack.pop();
}
}
}
/**
* Evaluates the expression and returns the result.
*
* <p>This method is only invoked by the super class {@link Expression} when calling {@link
* #eval(Environment)}.
*
* @throws EvalException if the expression could not be evaluated
* @throws InterruptedException may be thrown in a sub class.
*/
abstract Object doEval(Environment env) throws EvalException, InterruptedException;
@Override
public final void prettyPrint(Appendable buffer, int indentLevel) throws IOException {
prettyPrint(buffer);
}
/**
* Expressions should implement this method instead of {@link #prettyPrint(Appendable, int)},
* since the {@code indentLevel} argument is not needed.
*/
@Override
public abstract void prettyPrint(Appendable buffer) throws IOException;
/**
* Kind of the expression. This is similar to using instanceof, except that it's more efficient
* and can be used in a switch/case.
*/
public abstract Kind kind();
}
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