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[MOREL-25] Add
o (function composition) and @ (list concatenation…
…) operators
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,113 @@ | ||
| /* | ||
| * Licensed to Julian Hyde under one or more contributor license | ||
| * agreements. See the NOTICE file distributed with this work | ||
| * for additional information regarding copyright ownership. | ||
| * Julian Hyde 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. | ||
| */ | ||
| package net.hydromatic.morel.util; | ||
|
|
||
| import net.hydromatic.morel.ast.Ast; | ||
| import net.hydromatic.morel.ast.Op; | ||
|
|
||
| import java.util.List; | ||
| import java.util.Objects; | ||
| import java.util.function.Function; | ||
|
|
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| import static net.hydromatic.morel.ast.AstBuilder.ast; | ||
|
|
||
| /** | ||
| * Enable creating right-deep trees. | ||
| * | ||
| * @param <E> Element type | ||
| */ | ||
| public abstract class Folder<E> { | ||
| final E e; | ||
|
|
||
| Folder(E e) { | ||
| this.e = Objects.requireNonNull(e); | ||
| } | ||
|
|
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| abstract E combine(List<Folder<E>> list); | ||
|
|
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| public static <E> E combineAll(List<Folder<E>> list) { | ||
| if (list.size() == 0) { | ||
| throw new AssertionError(); | ||
| } | ||
| final Folder<E> head = list.get(0); | ||
| final List<Folder<E>> tail = list.subList(1, list.size()); | ||
| return head.combine(tail); | ||
| } | ||
|
|
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| private static <E> Folder<E> end(E e) { | ||
| return new End<>(e); | ||
| } | ||
|
|
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| /** Appends an element using "@". */ | ||
| public static void at(List<Folder<Ast.Exp>> list, Ast.Exp e) { | ||
| append(list, e, e1 -> op(e1, Op.AT)); | ||
| } | ||
|
|
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| /** Appends an element using "::". */ | ||
| public static void cons(List<Folder<Ast.Exp>> list, Ast.Exp e) { | ||
| append(list, e, e1 -> op(e1, Op.CONS)); | ||
| } | ||
|
|
||
| /** Adds an element to an empty list. */ | ||
| public static <E> void start(List<Folder<E>> list, E e) { | ||
| if (!list.isEmpty()) { | ||
| throw new AssertionError(); | ||
| } | ||
| list.add(end(e)); | ||
| } | ||
|
|
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| /** Adds an element and operator to a non-empty list. */ | ||
| private static <E> void append(List<Folder<E>> list, E e, | ||
| Function<E, Folder<E>> fn) { | ||
| if (list.isEmpty()) { | ||
| throw new AssertionError(); | ||
| } | ||
| @SuppressWarnings("unchecked") | ||
| final End<E> end = (End) list.get(list.size() - 1); | ||
| list.set(list.size() - 1, fn.apply(end.e)); | ||
| list.add(end(e)); | ||
| } | ||
|
|
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| /** Creates a folder that combines an expression with whatever follows | ||
| * using an infix operator. */ | ||
| private static Folder<Ast.Exp> op(Ast.Exp e, final Op at) { | ||
| return new Folder<Ast.Exp>(e) { | ||
| Ast.Exp combine(List<Folder<Ast.Exp>> list) { | ||
| final Ast.Exp rest = combineAll(list); | ||
| return ast.infixCall(e.pos.plus(rest.pos), at, e, rest); | ||
| } | ||
| }; | ||
| } | ||
|
|
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| /** Sub-class of {@code Folder} that marks the end of a list. | ||
| * | ||
| * @param <E> element type */ | ||
| private static class End<E> extends Folder<E> { | ||
| End(E e) { | ||
| super(e); | ||
| } | ||
|
|
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| E combine(List<Folder<E>> list) { | ||
| assert list.isEmpty(); | ||
| return e; | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // End Folder.java |
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