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--- a/parse/infer.c

+++ b/parse/infer.c

@@ -100,7 +100,8 @@

     return t;

 }

-static int tyoccurs(Inferstate *st, Type *t, Type *sub)

+/* prevents types that directly contain themselves. */

+static int tyinfinite(Inferstate *st, Type *t, Type *sub)

 {

     size_t i;

@@ -116,12 +117,12 @@

     switch (sub->type) {

         case Tystruct:

             for (i = 0; i < sub->nmemb; i++)

-                if (tyoccurs(st, t, decltype(sub->sdecls[i])))

+                if (tyinfinite(st, t, decltype(sub->sdecls[i])))

                     return 1;

             break;

         case Tyunion:

             for (i = 0; i < t->nmemb; i++) {

-                if (sub->udecls[i]->etype && tyoccurs(st, t, sub->udecls[i]->etype))

+                if (sub->udecls[i]->etype && tyinfinite(st, t, sub->udecls[i]->etype))

                     return 1;

             }

             break;

@@ -131,7 +132,7 @@

             return 0;

         default:

             for (i = 0; i < sub->nsub; i++)

-                if (tyoccurs(st, t, sub->sub[i]))

+                if (tyinfinite(st, t, sub->sub[i]))

                     return 1;

             break;

     }

@@ -170,7 +171,7 @@

         bsunion(t->cstrs, base->cstrs);

     else

         t->cstrs = bsdup(base->cstrs);

-    if (tyoccurs(st, t, NULL))

+    if (tyinfinite(st, t, NULL))

         fatal(t->line, "Type %s includes itself", tystr(t));

 }

@@ -328,6 +329,8 @@

     return (a->type == Tyvar && a->nsub > 0) || a->type == Tyarray || a->type == Tyslice;

 }

+/* prevents types that contain themselves in the unification;

+ * eg @a U (@a -> foo) */

 static int occurs(Type *a, Type *b)

 {

     size_t i;

--- a/parse/parse.h

+++ b/parse/parse.h

@@ -92,14 +92,17 @@

     Ty type;

     int tid;

     int line;

+

     int resolved;     /* Have we resolved the subtypes? Prevents infinite recursion. */

     int fixed;        /* Have we fixed the subtypes? Prevents infinite recursion. */

+

     Bitset *cstrs;    /* the type constraints matched on this type */

-    Node **cstrlist;  /* The names of the constraints on the type. Used to resolve/fill the bitset */

+    Node **cstrlist;  /* The names of the constraints on the type. Used to fill the bitset */

     size_t ncstrlist; /* The length of the constraint list above */

+

+    Type **sub;       /* sub-types; shared by all composite types */

     size_t nsub;      /* For compound types */

     size_t nmemb;     /* for aggregate types (struct, union) */

-    Type **sub;       /* sub-types; shared by all composite types */

     union {

         Node *aname;   /* Tyalias: alias name */

         Node *name;    /* Tyname: unresolved name */