add doc/types.md: notes

doc/types.md

@@ -0,0 +1,57 @@
+types representation
+--------------------
+
+builtin types: 1 bit
+user types: short as offset (25000+n).
+
+we also need a size, for all current types (x or y or ...)
+maxsize=15 (we collect only a certain number of types until we
+unify some into the next common upper type, and replace them by it)
+
+# 1-2 words:
+struct type {
+  uint32_t size:4;  # 0-15 size of types[]
+  uint32_t nil:1;
+  uint32_t num:1;
+  uint32_t bool:1;
+  uint32_t dbl:1;
+  uint32_t bits:24; # and 4-23 other coretype combinations as bit
+  uint32_t hint:1;  # hint in last type
+  uint32_t free:2;  #
+  short types[0-15];#range: max 32767 user types, max length: 15
+};
+
+type of types
+-------------
+parsed or strictly inferred types
+vs compile-time type hints (the most likely types)
+vs run-time observed types (traced-based, see luajit.
+  after some >hits we want to add an optimization on this type.)
+
+bits reflect 25000 offsets in potion.h
+0 nil
+1 num
+2 bool
+3 dbl
+4 int
+5 str
+7 closure ({sig}, result)
+8 tuple  of value (int=>any)
+10 file
+17 table of key=>value (str=>any)
+18 lick  of {str,any,any}
+...
+23 any
+24 user++
+
+type *unify_types(exp *eo, type *a, type *b, int a_is_upper_limit=TRUE);
+type *exact_unify(exp *eo, type *a, type *b);
+
+typeprim
+typeaggr
+typeobj
+typetuple
+typefun
+subtype
+param
+