| // Licensed to the Apache Software Foundation (ASF) under one |
| // or more contributor license agreements. See the NOTICE file |
| // distributed with this work for additional information |
| // regarding copyright ownership. The ASF licenses this file |
| // to you 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. |
| |
| #pragma once |
| |
| /** |
| * A tree of Expression objects represents the abstract syntax tree that comprises part of a |
| * PEG (Parsing Expression Grammar). Each grammar consists of one or more named rules, each |
| * of which has an expression tree associated with it. The format of the grammars is described |
| * in the following paper: |
| * |
| * "Parsing Expression Grammars: A Recognition-Based Syntactic Foundation". |
| * Bryan Ford, POPL, January 2004. http://bford.info/pub/lang/peg.pdf |
| * |
| * An Expression can be used by a code generator to produce the code for a parser, or alternatively, |
| * used directly to implement an interpreter to produce a parse tree based on the rules of the |
| * grammar. |
| * |
| * The types are as follows: |
| * |
| * ChoiceExpr - matches exactly one of the child expressions against the input. Each expression |
| * is tested in order, until a match is found, with the result being that of the child parse. |
| * Evaluation succeeds if one of the children matched. |
| * |
| * SequenceExpr - matches each of the child expressions, in order, following consecutively in the |
| * input. Evaluation succeeds if all children matched. |
| * |
| * AndExpr - Positive lookahead assertion. The single child expression is tested against the input, |
| * and evaluation succeeds if there is a match. Afterwards, the current position moved back to the |
| * location in the input where the lookahead test began. |
| * |
| * NotExpr - Negative lookahead assertion. The single child expression is tested against the input, |
| * and evaluation succeeds if the child *fails* to match. Afterwards, the current position moved |
| * back to the location in the input where the lookahead test began. |
| * |
| * OptExpr - The input is consumed if it matches, otherwise the position is left unchanged. In |
| * either case, the evaluation succeeds. |
| * |
| * StarExpr - The child expression is repeatedly evaluated against the input until no more matches |
| * occur. The evaluation always suceeds. The result is a list of 1 or more nodes. |
| * |
| * PlusExpr - The child expression is repeatedly evaluated against the input until no more matches |
| * occur. The evaluation always suceeds if at least one match was made. The result is a list of |
| * 1 or more nodes. |
| * |
| * IdentExpr - Reference to another rule defined in the grammar. Always has a value, representing |
| * the name of the rule, and when the grammar resolution algorithm (not yet implemented) is run, |
| * will have a single child pointing to the expression associated with the referenced rule. |
| * |
| * LitExpr - Literal match against a sequence of characters. Always has a value, representing |
| * the string to be matched, and has no child nodes. |
| * |
| * Class - Character class expression. Matches against any characters given in the children, |
| * all of which are range expressions. |
| * |
| * RangeExpr - Matches again a character that is between a specified minimum and maximum. Evaluation |
| * succeeds if the next input character c is such that start <= c < end. |
| */ |
| |
| typedef enum { |
| ChoiceExpr, |
| SequenceExpr, |
| AndExpr, |
| NotExpr, |
| OptExpr, |
| StarExpr, |
| PlusExpr, |
| IdentExpr, |
| LitExpr, |
| ClassExpr, |
| DotExpr, |
| RangeExpr, |
| } ExprKind; |
| |
| typedef struct Expression Expression; |
| |
| Expression *ExpressionNew(ExprKind kind, int count, Expression **children); |
| Expression *ExpressionNewValue(ExprKind kind, const char *value); |
| Expression *ExpressionNewRange(int lo, int hi); |
| void ExpressionFree(Expression *expr); |
| |
| ExprKind ExpressionKind(Expression *expr); |
| Expression *ExpressionChild(Expression *expr, int index); |
| int ExpressionCount(Expression *expr); |
| const char *ExpressionValue(Expression *expr); |
| int ExpressionStart(Expression *expr); |
| int ExpressionEnd(Expression *expr); |
| void ExpressionPrint(Expression *expr, int highestPrecedence, const char *indent); |