Implement decimal integer reading

lib/include/reader.h

@@ -0,0 +1,9 @@
+#ifndef READER_H
+#define READER_H
+
+#include "memory_pool.h"
+
+const expression_t *
+read_expression(memory_pool_t *pool, const char *input, int len);
+
+#endif

lib/reader.c

@@ -0,0 +1,21 @@
+#include "reader.h"
+
+#include <ctype.h>
+#include <stddef.h>
+
+const expression_t *
+read_expression(memory_pool_t *pool, const char *input, int len)
+{
+	expression_t *result = allocate_expression(pool);
+	if (NULL == result)
+		return NULL;
+	result->is_number = true;
+	result->number = 0;
+	while (isdigit(*input)) {
+		result->number *= 10;
+		result->number += *input - '0';
+		++input;
+		++len;
+	}
+	return result;
+}