diff --git a/engine/slc.h b/engine/slc.h
index 9fcc95e..809ec30 100644
--- a/engine/slc.h
+++ b/engine/slc.h
@@ -7,14 +7,118 @@ struct wordstart {
 	char colon;
 	/* whitespace after ':', usually used to store the flags */
 	uint8_t flags;
-	/* vars[] */
-	/* data[] */
+	/* char name[]; // The name of the word being defined. */
+	/* char vars[]; // The local variables of the word. */
+	/* char data[]; // The "body" of the word - either text source or after processing the threaded code of it (see flags) */
 };
 
-enum SYMOP { SYMOP_ADD, SYMOP_GET };
+enum SLC_SYM_OP { SLC_SYM_SET, SLC_SYM_GET, SLC_SYM_ERASE };
+enum SLC_STACK_OP { SLC_STACK_PUSH, SLC_STACK_POP, SLC_STACK_AT, SLC_STACK_COUNT, SLC_STACK_ERASE };
+enum SLC_SESSION_OP { SLC_SESSION_ALLOC, SLC_SESSION_ERASE, SLC_SESSION_GET };
+enum SLC_IO_OP {
+	SLC_IO_OPEN,
+	SLC_IO_OPEN_TMP,
+	SLC_IO_REMOVE_TMPS,
+	SLC_IO_CLOSE,
+	SLC_IO_READ,
+	SLC_IO_WRITE,
+	SLC_IO_LOCK,
+	SLC_IO_UNLOCK,
+	SLC_IO_CMD,
+};
 
-typedef void*(sym)(SYMOP op, char *key, wordstart **word);
-typedef void*(cstack)(SYMOP op, uint32_t );
+/**
+ * Function-abstraction for a "symbol-table".
+ *
+ * Operations:
+ *
+ * 		SLC_SYM_SET Saves a mapping from key->word in symbol table. word==NULL removes mapping. Returns ptr back or NULL on errors.
+ * 		SLC_SYM_GET Gets the symbol at key (the word parameter is unused). Returns NULL if there is no word for the key.
+ * 		SLC_SYM_ERASE Erases the symbol table so it becomes empty again. Can never fail, returns NULL.
+ *
+ * @param op Defines which operation the caller wants.
+ * @param key The key (both for SET and GET)
+ * @param word When adding a found word to the symbol table, the key will point to this word
+ * @returns The word definition stored for the key, or NULL when it is not stored yet or op is SET and there was an error.
+ */
+typedef wordstart* (*sym)(SLC_SYM_OP op, char *key, wordstart *word);
 
+/**
+ * Function-abstraction for an integer "stack".
+ *
+ * Operations:
+ * 
+ * 		SLC_STACK_PUSH pushes the "elem" to the stack. Returns 1 if succeeded, otherwise 0.
+ * 		SLC_STACK_POP pops the stack - does not return meaningful value, beware of underflowing!
+ * 		SLC_STACK_AT returns the "param"th element down from the top of the stack
+ * 		SLC_STACK_COUNT returns the number of elements in the stack
+ * 		SLC_STACK_ERASE Makes the stack empty. Basically as if you would POP the COUNT times.
+ *
+ * @param op Defines which operation the caller wants.
+ * @param param On SLC_STACK_PUSH, this is the element to push onto the stack, in case of SLC_STACK_AT, its the index.
+ * @return The element at the given stack location in case of SLC_STACK_AT or the count in case of SLC_STACK_COUNT. Can show error!
+ */
+typedef uint32_t (*stack)(SLC_STACK_OP op, uint32_t param);
+
+/**
+ * Function-abstraction for an integer "session-storage".
+ *
+ * Operations:
+ * 		SLC_SESSION_ALLOC allocates parameter amount of memory and returns an accessor index.
+ * 		SLC_SESSION_ERASE erase the session storage (all of it)
+ * 		SLC_SESSION_GET gets byte at the ith accessor index
+ *
+ * @param op Defines which operation the caller wants.
+ * @param i Used on SESSION_GET and is the accessor index
+ * @returns The accessor index in case of ALLOC (0xFFFFFFFF == -1 means error), on get it returns the store BYTE as uint32_t
+ */
+typedef uint32_t (*session)(SLC_SESSION_OP op, uint32_t i);
+
+/**
+ * Function-abstraction for io connectors.
+ *
+ * Operations:
+ *
+ * 		SLC_IO_OPEN Opens a PERSISTENT file with the given name. Returns the handle pointer (or NULL on error).
+ * 		SLC_IO_CLOSE Closes a PERSISTENT file with the given handle.
+ * 		SLC_IO_OPEN_TMP Opens a TEMPORARY file with the given name. Returns the handle pointer.
+ * 		SLC_IO_CLOSE_TMP Removes the TEMPORARY file with the given handle.
+ * 		SLC_IO_READ Reads a character from the given file handle. Returns pointer to the character that got read.
+ * 		SLC_IO_WRITE Writes a character from the given file handle. The 'param' points to the character to write (1 byte)
+ * 		SLC_IO_LOCK Locks the given file handle for exclusive reads and writes (others need to use lock/unlock too)
+ * 		SLC_IO_UNLOCK Locks the given file handle for exclusive reads and writes (others need to use lock/unlock too)
+ * 		SLC_IO_CMD Runs the given command on the operating system. The 'param' is the command (+args) and returned is std output.
+ *
+ * @param op Defines which operation the caller wants.
+ * @param param The name or temporary name or command or the handle pointer parameter depending on op.
+ * @returns A handle pointer or pointer to character to read / written or closed/unlocked handle (NULL on errors). Also cmd stdout.
+ */
+typedef const char* (*ioconn)(SLC_IO_OP op, const char *param);
+
+/**
+ * This function runs the main slc engine over a snippet of code.
+ *
+ * @param code The input source code to interpret / run.
+ * @param symbol_table The symbol table to use
+ * @param code_stack The code stack (return addresses) to use
+ * @param data_stack The data stack (forth-like stack) to use
+ * @param insert_stack Used for temporarily expanding the input stream (one word level above) with words
+ * @param session_storage Can allocate and use arbitrary memory with this.
+ * @param io_connector The engine uses this to open/close pipes/files and write/read them.
+ */
+void slc(
+	const char *code,
+	sym symbol_table,
+	stack code_stack,
+	stack data_stack,
+	stack insert_stack,
+	session session_storage,
+	ioconn io_connector,
+	const char *prefix,
+	const char *ender,
+	const char *varprefix,
+) {
+	// TODO
+}
 
 #ENDIF /* SLC_H */