Added uiOnShouldQuit() and its common code.

GNUmakefile

@@ -25,6 +25,7 @@ baseHFILES = \
 baseCFILES = \
 	box.c \
 	ptrarray.c \
+	shouldquit.c \
 	$(osCFILES)
 
 baseMFILES = $(osMFILES)

shouldquit.c

@@ -0,0 +1,22 @@
+// 9 may 2015
+#include "ui.h"
+#include "uipriv.h"
+
+static int defaultOnShouldQuit(void *data)
+{
+	return 0;
+}
+
+static int (*onShouldQuit)(void *) = defaultOnShouldQuit;
+static void *onShouldQuitData;
+
+void uiOnShouldQuit(int (*f)(void *), void *data)
+{
+	onShouldQuit = f;
+	onShouldQuitData = data;
+}
+
+int shouldQuit(void)
+{
+	return (*onShouldQuit)(onShouldQuitData);
+}

ui.idl

@@ -24,6 +24,8 @@ func FreeInitError(err *const char);
 func Main(void);
 func Quit(void);
 
+func OnShouldQuit(f *func(data *void) int, data *void);
+
 func FreeText(text *char);
 
 raw "typedef struct uiSizingSys uiSizingSys;";

uipriv.h

@@ -27,3 +27,6 @@ void ptrArrayAppend(struct ptrArray *, void *);
 void ptrArrayInsertBefore(struct ptrArray *, uintmax_t, void *);
 void ptrArrayDelete(struct ptrArray *, uintmax_t);
 #define ptrArrayIndex(p, T, i) ((T) ((p)->ptrs[(i)]))
+
+// shouldquit.c
+int shouldQuit(void);