Allow calling next on abstracts.

This will allow the creation of infinte
streams, low cost generators, etc.

src/core/inttypes.c

@@ -91,7 +91,8 @@ static const JanetAbstractType it_s64_type = {
     int64_unmarshal,
     it_s64_tostring,
     janet_int64_compare,
-    janet_int64_hash
+    janet_int64_hash,
+    NULL
 };
 
 static const JanetAbstractType it_u64_type = {
@@ -104,7 +105,8 @@ static const JanetAbstractType it_u64_type = {
     int64_unmarshal,
     it_u64_tostring,
     janet_uint64_compare,
-    janet_int64_hash
+    janet_int64_hash,
+    NULL
 };
 
 int64_t janet_unwrap_s64(Janet x) {

src/core/io.c

@@ -52,6 +52,7 @@ JanetAbstractType cfun_io_filetype = {
     NULL,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 

src/core/math.c

@@ -62,7 +62,8 @@ static JanetAbstractType JanetRNG_type = {
     janet_rng_unmarshal,
     NULL,
     NULL,
-    NULL
+    NULL,
+    NULL,
 };
 
 JanetRNG *janet_default_rng(void) {

src/core/parse.c

@@ -743,6 +743,7 @@ static JanetAbstractType janet_parse_parsertype = {
     NULL,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 

src/core/peg.c

@@ -1214,6 +1214,7 @@ static const JanetAbstractType peg_type = {
     peg_unmarshal,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 

src/core/thread.c

@@ -402,6 +402,7 @@ static JanetAbstractType Thread_AT = {
     NULL,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 

src/core/typedarray.c

@@ -121,6 +121,7 @@ static const JanetAbstractType ta_buffer_type = {
     ta_buffer_unmarshal,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 
@@ -287,6 +288,7 @@ static const JanetAbstractType ta_view_type = {
     ta_view_unmarshal,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 

src/core/util.c

@@ -427,6 +427,7 @@ static const JanetAbstractType type_wrap = {
     NULL,
     NULL,
     NULL,
+    NULL,
     NULL
 };
 

src/core/value.c

@@ -87,6 +87,12 @@ Janet janet_next(Janet ds, Janet key) {
             }
             break;
         }
+        case JANET_ABSTRACT: {
+            JanetAbstract abst = janet_unwrap_abstract(ds);
+            const JanetAbstractType *at = janet_abstract_type(abst);
+            if (NULL == at->next) break;
+            return at->next(abst, key);
+        }
     }
     return janet_wrap_nil();
 }

src/include/janet.h

@@ -907,6 +907,7 @@ struct JanetAbstractType {
     void (*tostring)(void *p, JanetBuffer *buffer);
     int (*compare)(void *lhs, void *rhs);
     int32_t (*hash)(void *p, size_t len);
+    Janet(*next)(void *p, Janet key);
 };
 
 struct JanetReg {