87 lines
3.0 KiB
Java
87 lines
3.0 KiB
Java
package function.builtin.special;
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import static function.builtin.EVAL.eval;
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import function.*;
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import sexpression.*;
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import table.*;
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@FunctionNames({ "LET" })
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public class LET extends LispSpecialFunction {
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private ArgumentValidator argumentValidator;
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private ArgumentValidator variableDefinitionListValidator;
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private ArgumentValidator pairValidator;
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private ExecutionContext executionContext;
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public LET() {
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this.argumentValidator = new ArgumentValidator("LET");
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this.argumentValidator.setMinimumNumberOfArguments(1);
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this.argumentValidator.setFirstArgumentExpectedType(Cons.class);
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this.variableDefinitionListValidator = new ArgumentValidator("LET|pair-list|");
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this.variableDefinitionListValidator.setEveryArgumentExpectedType(Cons.class);
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this.pairValidator = new ArgumentValidator("LET|pair|");
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this.pairValidator.setExactNumberOfArguments(2);
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this.pairValidator.setFirstArgumentExpectedType(Symbol.class);
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this.executionContext = ExecutionContext.getInstance();
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}
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public SExpression call(Cons argumentList) {
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argumentValidator.validate(argumentList);
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Cons variableDefinitions = (Cons) argumentList.getFirst();
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Cons body = (Cons) argumentList.getRest();
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return evaluateInScope(variableDefinitions, body);
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}
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private SExpression evaluateInScope(Cons variableDefinitions, Cons body) {
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SymbolTable localScope = createLocalScope(variableDefinitions);
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SExpression lastEvaluation = evaluateBody(body);
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restorePreviousScope(localScope);
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return lastEvaluation;
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}
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private SymbolTable createLocalScope(Cons variableDefinitions) {
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SymbolTable localScope = new SymbolTable(executionContext.getScope());
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addVariablesToScope(localScope, variableDefinitions);
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executionContext.setScope(localScope);
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return localScope;
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}
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private void addVariablesToScope(SymbolTable scope, Cons variableDefinitions) {
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variableDefinitionListValidator.validate(variableDefinitions);
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for (; variableDefinitions.isCons(); variableDefinitions = (Cons) variableDefinitions.getRest())
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addPairToScope((Cons) variableDefinitions.getFirst(), scope);
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}
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private void addPairToScope(Cons symbolValuePair, SymbolTable scope) {
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pairValidator.validate(symbolValuePair);
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Cons restOfPair = (Cons) symbolValuePair.getRest();
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SExpression symbol = symbolValuePair.getFirst();
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SExpression value = restOfPair.getFirst();
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scope.put(symbol.toString(), eval(value));
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}
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private SExpression evaluateBody(Cons body) {
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SExpression lastEvaluation = Nil.getInstance();
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for (; body.isCons(); body = (Cons) body.getRest())
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lastEvaluation = eval(body.getFirst());
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return lastEvaluation;
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}
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private void restorePreviousScope(SymbolTable localScope) {
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executionContext.setScope(localScope.getParent());
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}
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}
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