begin work on new lexer

src/stream.c

@@ -0,0 +1,39 @@
+#include "stream.h"
+#include <stdio.h>
+
+static int filestream_getc(void *f) { return fgetc((FILE *)f); }
+static int filestream_ungetc(int c, void *f) { return ungetc(c, (FILE *)f); }
+static int filestream_eof(void *f) { return feof((FILE *)f); }
+
+static int bufstream_getc(void *f) {
+  Buf *b = f;
+  if (b->unread != -1) {
+    int c = b->unread;
+    b->unread = -1;
+    return c;
+  } else if (b->pos >= b->len) {
+    return -1;
+  }
+  return b->data[b->pos++];
+}
+
+static int bufstream_ungetc(int c, void *f) { return ((Buf *)f)->unread = c; }
+
+static int bufstream_eof(void *f) {
+  Buf *b = f;
+  if (b->unread != -1)
+    return 0;
+  return b->pos >= b->len;
+}
+
+// clang-format off
+static const StreamVtable _filestream_vtable = {
+  filestream_getc, filestream_ungetc, filestream_eof
+};
+const StreamVtable *filestream_vtable = &_filestream_vtable;
+
+static const StreamVtable _bufstream_vtable = {
+  bufstream_getc, bufstream_ungetc, bufstream_eof
+};
+const StreamVtable *bufstream_vtable = &_bufstream_vtable;
+// clang-format on