go/types: add testdata/map2.go2, update README

Change-Id: I5a859fe3298998810ba56f3b445fae8e1d177995

src/go/types/README

@@ -2,7 +2,7 @@ This code contains changes to go/types and the go/* support libraries
 to type-check generic code as outlined in the latest contracts proposal
 and presented by Ian Lance Taylor at GopherCon 2019 in San Diego.
 
-CAUTION: EARLY PROTOTYPE. A LOT IS STILL MISSING. THERE ARE MANY BUGS.
+CAUTION: EARLY PROTOTYPE. MISSING PIECES. THERE ARE BUGS.
 
 Read and use the code at your own risk.
 
@@ -10,31 +10,26 @@ That said, the go/parser and go/ast changes are working and pass tests
 including all the larger examples in the latest contracts design doc.
 Look for the *.go2 files in go/parser/testdata.
 
-gofmt does not work with parameterized code yet.
+gofmt works only partly with parameterized code.
 
-The type-checker is starting to work but has still many problems.
+The type-checker is starting to work but is not complete.
 I will update this CL from time to time as progress happens.
 
 Specifically, the following pieces (and more) are missing from type-
 checking or lead to unexpected behavior:
 
 - Importing of packages with type parameters or contracts.
-- Type-checking of contracts and type parameter lists with contracts.
-  For instance, because contracts are not yet type-checked, maps where
-  the key type is a type parameter will lead to an error because the
-  type checker doesn't know whether the key type is comparable or not.
-- Parameterized alias types.
-- Type instantiation is not always working as expected, leading to
-  some odd error messages.
-- Methods with parameterized receiver types have only recently started
-  to work; there are a few issues around them with proper type
-  instantiation.
+- Type-checking of contracts is limited to contracts with methods.
+- Methods with parameterized receiver types are not implemented yet.
 
 The following is "working" (as in: can be type-checked without errors):
 
-- Declaration and use of simple parameterized types without contracts.
-- Declaration and use (calls) of simple parameterized functions without
-  contracts, including type inference from function arguments.
+- Declaration and use of parameterized types.
+- Declaration and use (calls) of parameterized functions,
+  including type inference from function arguments.
+- Some larger tests pass mostly (see testdata/*.go2 files).
+
+Some code may look like it's working, but it may simply not do anything.
 
 Error messages, where present, are in usable condition but expect
 them to be significantly better in a more complete implementation.
@@ -42,7 +37,7 @@ them to be significantly better in a more complete implementation.
 To play with this prototype:
 
 - Cherry-pick this CL on top of tip (the cherry-pick was tested with
-  tip at 919594830f17):
+  tip at 4983a0b75b40):
 
   git fetch "https://go.googlesource.com/go" ... && git cherry-pick FETCH_HEAD
 

src/go/types/check_test.go

@@ -110,6 +110,7 @@ var tests = [][]string{
 	{"testdata/slices.go2"},
 	{"testdata/chans.go2"},
 	{"testdata/map.go2"},
+	{"testdata/map2.go2"},
 }
 
 var fset = token.NewFileSet()

src/go/types/testdata/map2.go2

@@ -0,0 +1,139 @@
+// This file is like map.go2, but instead if importing chans, it contains
+// the necessary functionality at the end of the file.
+
+// Package orderedmap provides an ordered map, implemented as a binary tree.
+package orderedmap
+
+// Map is an ordered map.
+type Map(type K, V) struct {
+	root    *node(K, V)
+	compare func(K, K) int
+}
+
+// node is the type of a node in the binary tree.
+type node(type K, V) struct {
+	key         K
+	val         V
+	left, right *node(K, V)
+}
+
+// New returns a new map.
+func New(type K, V)(compare func(K, K) int) *Map(K, V) {
+        return &Map(K, V){compare: compare}
+}
+
+// find looks up key in the map, and returns either a pointer
+// to the node holding key, or a pointer to the location where
+// such a node would go.
+func (m *Map(K, V)) find(key K) **node(K, V) {
+	pn := &m.root
+	for *pn != nil {
+		switch cmp := m.compare(key, (*pn).key); {
+		case cmp < 0:
+			pn = &(*pn).left
+		case cmp > 0:
+			pn = &(*pn).right
+		default:
+			return pn
+		}
+	}
+	return pn
+}
+
+// Insert inserts a new key/value into the map.
+// If the key is already present, the value is replaced.
+// Returns true if this is a new key, false if already present.
+func (m *Map(K, V)) Insert(key K, val V) bool {
+	pn := m /* ERROR not implemented */ .find(key)
+	if *pn != nil {
+		(*pn).val = val
+		return false
+	}
+        *pn = &node(K, V){key: key, val: val}
+	return true
+}
+
+// Find returns the value associated with a key, or zero if not present.
+// The found result reports whether the key was found.
+func (m *Map(K, V)) Find(key K) (V, bool) {
+	pn := m /* ERROR not implemented */ .find(key)
+	if *pn == nil {
+		var zero V // see the discussion of zero values, above
+		return zero, false
+	}
+	return (*pn).val, true
+}
+
+// keyValue is a pair of key and value used when iterating.
+type keyValue(type K, V) struct {
+	key K
+	val V
+}
+
+// InOrder returns an iterator that does an in-order traversal of the map.
+func (m *Map(K, V)) InOrder() *Iterator(K, V) {
+	sender, receiver := chans_Ranger(keyValue(K, V))()
+	var f func(*node(K, V)) bool
+	f = func(n *node(K, V)) bool {
+		if n == nil {
+			return true
+		}
+		// Stop sending values if sender.Send returns false,
+		// meaning that nothing is listening at the receiver end.
+		return f(n.left) &&
+                        // TODO
+			// sender.Send(keyValue(K, V){n.key, n.val}) &&
+			f(n.right)
+	}
+	go func() {
+		f(m.root)
+		sender /* ERROR not implemented */ .Close()
+	}()
+	// TODO(gri) The design draft doesn't require that we repeat
+	// the type parameters here. Fix the implementation.
+        _ = receiver
+        panic(0)
+	//return &Iterator(K, V){receiver}
+	// return &Iterator{receiver}
+}
+
+// Iterator is used to iterate over the map.
+type Iterator(type K, V) struct {
+	r *chans_Receiver(keyValue(K, V))
+}
+
+// Next returns the next key and value pair, and a boolean indicating
+// whether they are valid or whether we have reached the end.
+func (it *Iterator(K, V)) Next() (K, V, bool) {
+	keyval, ok := it /* ERROR not implemented */ .r.Next()
+	if !ok {
+		var zerok K
+		var zerov V
+		return zerok, zerov, false
+	}
+	return keyval.key, keyval.val, true
+}
+
+// chans
+
+func chans_Ranger(type T)() (*chans_Sender(T), *chans_Receiver(T))
+
+// A sender is used to send values to a Receiver.
+type chans_Sender(type T) struct {
+	values chan<- T
+	done <-chan bool
+}
+
+func (s *chans_Sender(T)) Close() {
+	close(s.values)
+}
+
+type chans_Receiver(type T) struct {
+	values <-chan T
+	done chan<- bool
+}
+
+func (r *chans_Receiver(T)) Next() (T, bool) {
+	v, ok := <-r.values
+	return v, ok
+}