Make '=..'/2 work according to spec. Introduce types.c for functions which tells us something about term types. Should be used a lot more instead of explicitly looking into terms->tag everywhere

1 files changed, 58 insertions, 0 deletions

diff --git a/types.c b/types.c
new file mode 100644
index 0000000..6f2b33d
--- /dev/null
+++ b/types.c
@@ -0,0 +1,58 @@
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+
+#include "dat.h"
+#include "fns.h"
+
+/* Type tests */
+int
+islist(Term *t)
+{
+	return (isemptylist(t) || isnonemptylist(t));
+}
+
+int
+ispartiallist(Term *t)
+{
+	if(t->tag == VariableTerm)
+		return 1;
+	else if(t->tag == CompoundTerm && runestrcmp(t->text, L".") == 0 && t->arity == 2)
+		return ispartiallist(listtail(t));
+	else
+		return 0;
+}
+
+int
+isemptylist(Term *t)
+{
+	return (t->tag == AtomTerm && runestrcmp(t->text, L"[]") == 0);
+}
+
+int
+isnonemptylist(Term *t)
+{
+	if(t->tag == CompoundTerm && runestrcmp(t->text, L".") == 0 && t->arity == 2)
+		return islist(listtail(t));
+	else
+		return 0;	
+}
+
+/* Other functions */
+Term *
+listhead(Term *t)
+{
+	if(t->tag == CompoundTerm && runestrcmp(t->text, L".") == 0 && t->arity == 2)
+		return t->children;
+	else
+		return nil;
+}
+
+Term *
+listtail(Term *t)
+{
+	if(t->tag == CompoundTerm && runestrcmp(t->text, L".") == 0 && t->arity == 2)
+		return t->children->next;
+	else
+		return nil;
+}
\ No newline at end of file