Create expression struct and memory pool

lib/include/expression.h

@@ -0,0 +1,27 @@
+#ifndef EXPRESSION_H
+#define EXPRESSION_H
+
+#include <stdbool.h>
+
+typedef enum {
+	OPERATOR_ADD,
+	OPERATOR_SUBTRACT,
+	OPERATOR_MULTIPLY,
+	OPERATOR_DIVIDE,
+} operator_t;
+
+struct _expression_t;
+typedef struct {
+	operator_t operator;
+	const struct _expression_t *operands[2];
+} application_t;
+
+typedef struct _expression_t {
+	bool is_number;
+	union {
+		application_t application;
+		int number;
+	};
+} expression_t;
+
+#endif

lib/include/memory_pool.h

@@ -0,0 +1,16 @@
+#ifndef MEMORY_POOL_H
+#define MEMORY_POOL_H
+
+#include "expression.h"
+
+#define MEMORY_POOL_SIZE 128U
+
+typedef struct {
+	expression_t buffer[MEMORY_POOL_SIZE];
+	expression_t *free_pointer;
+} memory_pool_t;
+
+void init_memory_pool(memory_pool_t *pool);
+expression_t *allocate_expression(memory_pool_t *pool);
+
+#endif

lib/memory_pool.c

@@ -0,0 +1,15 @@
+#include "memory_pool.h"
+
+#include <stddef.h>
+
+void init_memory_pool(memory_pool_t *pool)
+{
+	pool->free_pointer = &pool->buffer[0];
+}
+
+expression_t *allocate_expression(memory_pool_t *pool)
+{
+	if (pool->free_pointer > pool->buffer + MEMORY_POOL_SIZE)
+		return NULL;
+	return pool->free_pointer++;
+}