initial commit

java/expression/common/Reason.java

@@ -0,0 +1,60 @@
+package expression.common;
+
+import base.Either;
+
+import java.util.function.LongUnaryOperator;
+import java.util.function.Supplier;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public final class Reason {
+    public static final Reason OVERFLOW = new Reason("Overflow");
+    public static final Reason DBZ = new Reason("Division by zero");
+
+    private final String description;
+
+    public Reason(final String description) {
+        this.description = description;
+    }
+
+    public static <T> Either<Reason, T> eval(final Supplier<T> action) {
+        try {
+            return Either.right(action.get());
+        } catch (final ReasonException e) {
+            return Either.left(e.reason);
+        }
+    }
+
+    public static int overflow(final long value) {
+        return value < Integer.MIN_VALUE || Integer.MAX_VALUE < value
+                ? OVERFLOW.error()
+                : (int) value;
+    }
+
+    public <T> T error() {
+        throw new ReasonException(this);
+    }
+
+    public LongUnaryOperator less(final long limit, final LongUnaryOperator op) {
+        return a -> a < limit ? error() : op.applyAsLong(a);
+    }
+
+    public LongUnaryOperator greater(final int limit, final LongUnaryOperator op) {
+        return a -> a > limit ? error() : op.applyAsLong(a);
+    }
+
+    private static class ReasonException extends RuntimeException {
+        private final Reason reason;
+
+        public ReasonException(final Reason reason) {
+            super(reason.description);
+            this.reason = reason;
+        }
+    }
+
+    @Override
+    public String toString() {
+        return String.format("Reason(%s)", description);
+    }
+}