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package org.zwobble.couscous.transforms;
import org.zwobble.couscous.ast.LocalVariableDeclarationNode;
import org.zwobble.couscous.ast.NodeTypes;
import org.zwobble.couscous.ast.StatementNode;
import org.zwobble.couscous.ast.sugar.SwitchCaseNode;
import org.zwobble.couscous.ast.sugar.SwitchNode;
import org.zwobble.couscous.ast.visitors.NodeTransformer;
import org.zwobble.couscous.frontends.java.Scope;
import org.zwobble.couscous.types.Types;
import org.zwobble.couscous.util.ExtraLists;
import java.util.List;
import static com.google.common.collect.Iterables.tryFind;
import static org.zwobble.couscous.ast.IfStatementNode.ifStatement;
import static org.zwobble.couscous.ast.MethodCallNode.methodCall;
import static org.zwobble.couscous.ast.TypeCoercionNode.coerce;
import static org.zwobble.couscous.ast.VariableReferenceNode.reference;
import static org.zwobble.couscous.ast.sugar.SwitchCaseNode.switchCase;
import static org.zwobble.couscous.util.ExtraIterables.lazyFlatMap;
import static org.zwobble.couscous.util.ExtraLists.*;
import static org.zwobble.couscous.util.Fold.foldRight;
import static org.zwobble.couscous.util.Tails.tails;
import static org.zwobble.couscous.util.UpToAndIncludingIterable.upToAndIncluding;
public class DesugarSwitchToIfElse {
// TODO: ensure globally unique IDs, and locally unique variable names
public static NodeTransformer transformer() {
Scope scope = Scope.create().temporaryPrefix("_couscous_desugar_switch_to_if");
return DesugarStatement.<SwitchNode>transformer(NodeTypes.SWITCH, node -> desugar(scope, node));
}
public static List<StatementNode> desugar(Scope scope, SwitchNode switchNode) {
LocalVariableDeclarationNode switchValueAssignment = scope.temporaryVariable(switchNode.getValue());
List<StatementNode> handleDefault = tryFind(switchNode.getCases(), SwitchCaseNode::isDefault)
.transform(SwitchCaseNode::getStatements)
.or(list());
List<SwitchCaseNode> cases = eagerMap(
tails(switchNode.getCases()),
remainingCases -> readSwitchCase(remainingCases.get(0), remainingCases)
);
return cons(
switchValueAssignment,
foldRight(cases, handleDefault, (handle, currentCase) ->
currentCase.getValue()
.map(value -> list(ifStatement(
methodCall(
reference(switchValueAssignment),
"equals",
list(coerce(value, Types.OBJECT)),
Types.BOOLEAN
),
currentCase.getStatements(),
handle
)))
.orElse(handle)
)
);
}
private static SwitchCaseNode readSwitchCase(SwitchCaseNode caseStatement, List<SwitchCaseNode> cases)
{
Iterable<StatementNode> statementsForCase = upToAndIncluding(
lazyFlatMap(cases, SwitchCaseNode::getStatements),
DesugarSwitchToIfElse::isEndOfCase
);
return switchCase(
caseStatement.getValue(),
ExtraLists.copyOf(statementsForCase)
);
}
private static boolean isEndOfCase(StatementNode statement) {
return statement.type() == NodeTypes.RETURN;
}
}
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