Update spec.md

spec.md

@@ -345,8 +345,7 @@ The only operator with type overloading
 TODO
 
 
-# coding patterns (for users only)
+# (for users) programming patterns
-
 ## labelled arguments
 ```
 def List.remove_prefix(prefix: t List, list: 'from t List)
@@ -357,6 +356,39 @@ List.remove_prefix([1,2], 'from [1,2,3,4])
 List.remove_prefix([1,2], [1,2,3,4])
 ```
 
+## promising a list of at least one element
+Returning a `'Cons {v: Int, next: Int List}`
+indicates that the list contains at least one element.
+And this is even assignable to `Int List`
+
+
+# (for implementors) recommendations
+## Don't do deep-copies of type objects
+types could have hundreds of enum cases
+
+
+## Store original type alias names in types, as hints
+To give more information to the user in error messages
+
+Which of these is more readable and user friendly...
+- `&a {v: 'None | 'Some {high:Int16,low:Int16}, next: a}`
+- `Int32 Option List`
+
+
+## Perform fuzzy match to give suggestions for correcting errors
+Non-nominal record types have the issue of typos propagating really far trough the code,
+making them hard to debug.
+
+Give fuzzy-matched suggestions for at the following things:
+- function names
+- local names
+- non-nominal record fields
+- union tags
+
+
+## Store as much debug in fromation as possible until type checking is done
+
+
 
 # OLD SPECIFICATION STARTING HERE
 ## automatic return types
@@ -366,20 +398,6 @@ def add(a: Num, b: Num) -> _ {
 }
 ```
 
-## templated generics
-```
-# Type of add is:   template a, b: a -> b -> _
-def [a,b] add(a: a, b: b) -> _ {
-  a + b
-}
-
-add(1,2)
-
-add(1)(2)  # error: partial function application of templated functions not allowed
-
-add(1,"2")    # error: in template expansion of add[Num,List[Char]]: No definition for `Num + List[Char]`
-```
-
 ## pattern matching
 ```
 type Option[t] = 'None | 'Some t