First commit

.gitignore

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+average
+*.swp

CC0

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+CC0 1.0 Universal
+
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Makefile

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+all: average
+
+clean:
+	rm -f average
+
+.PHONY: all clean

average.c

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+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+
+#include "cmaybe.h"
+
+MAYBE_TYPE(intmax_t, intmax_t);
+
+MAYBE(intmax_t) average(intmax_t numbers[], size_t length) {
+	ENABLE_RETURN(intmax_t);
+	if (length == 0)
+		RETURN_NOTHING();
+
+	intmax_t sum = 0;
+	for (size_t i = 0; i < length; i++) {
+		intmax_t num = numbers[i];
+		if (num > 0 && INTMAX_MAX - num < sum) {
+			RETURN_NOTHING();
+		} else if (num < 0 && INTMAX_MIN - num > sum) {
+			RETURN_NOTHING();
+		} else {
+			sum += num;
+		}
+	}
+
+	RETURN_VALUE(sum/length);
+}
+
+int main(void) {
+	intmax_t numbers[] = {5, 7, 1, -8, INTMAX_MAX};
+	MAYBE(intmax_t) results[6];
+	results[0] = average(numbers, 0);
+	results[1] = average(numbers, 1);
+	results[2] = average(numbers, 2);
+	results[3] = average(numbers, 3);
+	results[4] = average(numbers, 4);
+	results[5] = average(numbers, 5);
+
+	for(size_t i = 0; i < sizeof(results) / sizeof(MAYBE(intmax_t)); i++) {
+		IS_VALUE(results[i]) {
+			printf("%zu: %jd\n", i, VALUE(results[i]));
+		} else {
+			printf("%zu: No value\n", i);
+		}
+	}
+
+	return 0;
+}

cmaybe.h

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+#define MAYBE_TYPE(name, type) struct maybe_##name {type value; char is_value;}
+#define MAYBE(name) struct maybe_##name
+
+#define ENABLE_RETURN(type) MAYBE(type) __return_value
+#define RETURN_VALUE(x) {\
+	__return_value.is_value = 1;\
+	__return_value.value = x;\
+	return __return_value;\
+}
+#define RETURN_NOTHING() {\
+	__return_value.is_value = 0;\
+	return __return_value;\
+}
+
+#define IS_VALUE(x) if((x).is_value)
+#define IS_NOT_VALUE(x) if(!(x).is_value)
+#define VALUE(x) (x).value