Added stream_till and stream_while helpers

Allows more abstract movement around the stream.

alisp.h

@@ -158,7 +158,14 @@ sv_t stream_substr(stream_t *, u64);
 // given size.
 sv_t stream_substr_abs(stream_t *, u64, u64);
 
-/// Basic defintions for a Lisp
+// Skip forward in stream till one of the characters in the given C string is
+// encountered.
+sv_t stream_till(stream_t *, const char *);
+// Skip forward in stream while one of the characters in the given C string is
+// present.
+sv_t stream_while(stream_t *, const char *);
+
+/// Lisp type definitions
 #define NIL 0
 
 typedef struct Obj lisp_t;

stream.c

@@ -339,3 +339,31 @@ sv_t stream_substr_abs(stream_t *stream, u64 index, u64 size)
     return SV(NULL, 0);
   }
 }
+
+sv_t stream_till(stream_t *stream, const char *str)
+{
+  if (stream_eoc(stream))
+    return SV(NULL, 0);
+  u64 current_position = stream->position;
+  for (char c = stream_peek(stream); c != '\0' && strchr(str, c) == NULL;
+       c      = stream_next(stream))
+    continue;
+  u64 size = stream->position - current_position;
+  if (size == 0)
+    return SV(NULL, 0);
+  return stream_substr_abs(stream, current_position, size - 1);
+}
+
+sv_t stream_while(stream_t *stream, const char *str)
+{
+  if (stream_eoc(stream))
+    return SV(NULL, 0);
+  u64 current_position = stream->position;
+  for (char c = stream_peek(stream); c != '\0' && strchr(str, c);
+       c      = stream_next(stream))
+    continue;
+  u64 size = stream->position - current_position;
+  if (size == 0)
+    return SV(NULL, 0);
+  return stream_substr_abs(stream, current_position, size - 1);
+}