1 files changed, 199 insertions, 0 deletions
diff --git a/libgo/go/exp/eval/scope.go b/libgo/go/exp/eval/scope.go
new file mode 100644
index 00000000000..8eee38e0340
--- /dev/null
+++ b/libgo/go/exp/eval/scope.go
@@ -0,0 +1,199 @@
+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package eval
+
+import (
+	"go/token"
+	"log"
+)
+
+/*
+ * Blocks and scopes
+ */
+
+// A definition can be a *Variable, *Constant, or Type.
+type Def interface {
+	Pos() token.Position
+}
+
+type Variable struct {
+	token.Position
+	// Index of this variable in the Frame structure
+	Index int
+	// Static type of this variable
+	Type Type
+	// Value of this variable.  This is only used by Scope.NewFrame;
+	// therefore, it is useful for global scopes but cannot be used
+	// in function scopes.
+	Init Value
+}
+
+type Constant struct {
+	token.Position
+	Type  Type
+	Value Value
+}
+
+// A block represents a definition block in which a name may not be
+// defined more than once.
+type block struct {
+	// The block enclosing this one, including blocks in other
+	// scopes.
+	outer *block
+	// The nested block currently being compiled, or nil.
+	inner *block
+	// The Scope containing this block.
+	scope *Scope
+	// The Variables, Constants, and Types defined in this block.
+	defs map[string]Def
+	// The index of the first variable defined in this block.
+	// This must be greater than the index of any variable defined
+	// in any parent of this block within the same Scope at the
+	// time this block is entered.
+	offset int
+	// The number of Variables defined in this block.
+	numVars int
+	// If global, do not allocate new vars and consts in
+	// the frame; assume that the refs will be compiled in
+	// using defs[name].Init.
+	global bool
+}
+
+// A Scope is the compile-time analogue of a Frame, which captures
+// some subtree of blocks.
+type Scope struct {
+	// The root block of this scope.
+	*block
+	// The maximum number of variables required at any point in
+	// this Scope.  This determines the number of slots needed in
+	// Frame's created from this Scope at run-time.
+	maxVars int
+}
+
+func (b *block) enterChild() *block {
+	if b.inner != nil && b.inner.scope == b.scope {
+		log.Panic("Failed to exit child block before entering another child")
+	}
+	sub := &block{
+		outer:  b,
+		scope:  b.scope,
+		defs:   make(map[string]Def),
+		offset: b.offset + b.numVars,
+	}
+	b.inner = sub
+	return sub
+}
+
+func (b *block) exit() {
+	if b.outer == nil {
+		log.Panic("Cannot exit top-level block")
+	}
+	if b.outer.scope == b.scope {
+		if b.outer.inner != b {
+			log.Panic("Already exited block")
+		}
+		if b.inner != nil && b.inner.scope == b.scope {
+			log.Panic("Exit of parent block without exit of child block")
+		}
+	}
+	b.outer.inner = nil
+}
+
+func (b *block) ChildScope() *Scope {
+	if b.inner != nil && b.inner.scope == b.scope {
+		log.Panic("Failed to exit child block before entering a child scope")
+	}
+	sub := b.enterChild()
+	sub.offset = 0
+	sub.scope = &Scope{sub, 0}
+	return sub.scope
+}
+
+func (b *block) DefineVar(name string, pos token.Position, t Type) (*Variable, Def) {
+	if prev, ok := b.defs[name]; ok {
+		return nil, prev
+	}
+	v := b.defineSlot(t, false)
+	v.Position = pos
+	b.defs[name] = v
+	return v, nil
+}
+
+func (b *block) DefineTemp(t Type) *Variable { return b.defineSlot(t, true) }
+
+func (b *block) defineSlot(t Type, temp bool) *Variable {
+	if b.inner != nil && b.inner.scope == b.scope {
+		log.Panic("Failed to exit child block before defining variable")
+	}
+	index := -1
+	if !b.global || temp {
+		index = b.offset + b.numVars
+		b.numVars++
+		if index >= b.scope.maxVars {
+			b.scope.maxVars = index + 1
+		}
+	}
+	v := &Variable{token.Position{}, index, t, nil}
+	return v
+}
+
+func (b *block) DefineConst(name string, pos token.Position, t Type, v Value) (*Constant, Def) {
+	if prev, ok := b.defs[name]; ok {
+		return nil, prev
+	}
+	c := &Constant{pos, t, v}
+	b.defs[name] = c
+	return c, nil
+}
+
+func (b *block) DefineType(name string, pos token.Position, t Type) Type {
+	if _, ok := b.defs[name]; ok {
+		return nil
+	}
+	nt := &NamedType{pos, name, nil, true, make(map[string]Method)}
+	if t != nil {
+		nt.Complete(t)
+	}
+	b.defs[name] = nt
+	return nt
+}
+
+func (b *block) Lookup(name string) (bl *block, level int, def Def) {
+	for b != nil {
+		if d, ok := b.defs[name]; ok {
+			return b, level, d
+		}
+		if b.outer != nil && b.scope != b.outer.scope {
+			level++
+		}
+		b = b.outer
+	}
+	return nil, 0, nil
+}
+
+func (s *Scope) NewFrame(outer *Frame) *Frame { return outer.child(s.maxVars) }
+
+/*
+ * Frames
+ */
+
+type Frame struct {
+	Outer *Frame
+	Vars  []Value
+}
+
+func (f *Frame) Get(level int, index int) Value {
+	for ; level > 0; level-- {
+		f = f.Outer
+	}
+	return f.Vars[index]
+}
+
+func (f *Frame) child(numVars int) *Frame {
+	// TODO(austin) This is probably rather expensive.  All values
+	// require heap allocation and zeroing them when we execute a
+	// definition typically requires some computation.
+	return &Frame{f, make([]Value, numVars)}
+}