go/usr/austin/eval/decls.go

// 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 (
	"bignum";
	"go/token";
)

/*
 * Types
 */

type Type interface {
	// compat returns whether this type is compatible with another
	// type.  If conv is false, this is normal compatibility,
	// where two named types are compatible only if they are the
	// same named type.  If conv if true, this is conversion
	// compatibility, where two named types are conversion
	// compatible if their definitions are conversion compatible.
	//
	// TODO(austin) Deal with recursive types
	compat(o Type, conv bool) bool;
	// lit returns this type's literal.  If this is a named type,
	// this is the unnamed underlying type.  Otherwise, this is an
	// identity operation.
	lit() Type;
	// isBoolean returns true if this is a boolean type.
	isBoolean() bool;
	// isInteger returns true if this is an integer type.
	isInteger() bool;
	// isFloat returns true if this is a floating type.
	isFloat() bool;
	// isIdeal returns true if this is an ideal int or float.
	isIdeal() bool;
	// Zero returns a new zero value of this type.
	Zero() Value;
	// String returns the string representation of this type.
	String() string;
	// The position where this type was defined, if any.
	Pos() token.Position;
}

type BoundedType interface {
	Type;
	// minVal returns the smallest value of this type.
	minVal() *bignum.Rational;
	// maxVal returns the largest value of this type.
	maxVal() *bignum.Rational;
}

/*
 * Values
 */

type Value interface {
	String() string;
	// Assign copies another value into this one.  It should
	// assume that the other value satisfies the same specific
	// value interface (BoolValue, etc.), but must not assume
	// anything about its specific type.
	Assign(o Value);
}

type BoolValue interface {
	Value;
	Get() bool;
	Set(bool);
}

type UintValue interface {
	Value;
	Get() uint64;
	Set(uint64);
}

type IntValue interface {
	Value;
	Get() int64;
	Set(int64);
}

// TODO(austin) IdealIntValue and IdealFloatValue should not exist
// because ideals are not l-values.
type IdealIntValue interface {
	Value;
	Get() *bignum.Integer;
}

type FloatValue interface {
	Value;
	Get() float64;
	Set(float64);
}

type IdealFloatValue interface {
	Value;
	Get() *bignum.Rational;
}

type StringValue interface {
	Value;
	Get() string;
	Set(string);
}

type ArrayValue interface {
	Value;
	// TODO(austin) Get() is here for uniformity, but is
	// completely useless.  If a lot of other types have similarly
	// useless Get methods, just special-case these uses.
	Get() ArrayValue;
	Elem(i int64) Value;
	// From returns an ArrayValue backed by the same array that
	// starts from element i.
	From(i int64) ArrayValue;
}

type StructValue interface {
	Value;
	// TODO(austin) This is another useless Get()
	Get() StructValue;
	Field(i int) Value;
}

type PtrValue interface {
	Value;
	Get() Value;
	Set(Value);
}

type Func interface {
	NewFrame() *Frame;
	Call(*Frame);
}

type FuncValue interface {
	Value;
	Get() Func;
	Set(Func);
}

type Slice struct {
	Base ArrayValue;
	Len, Cap int64;
}

type SliceValue interface {
	Value;
	Get() Slice;
	Set(Slice);
}

type Map interface {
	Len() int64;
	// Retrieve an element from the map, returning nil if it does
	// not exist.
	Elem(key interface{}) Value;
	// Set an entry in the map.  If val is nil, delete the entry.
	SetElem(key interface{}, val Value);
	// TODO(austin)  Perhaps there should be an iterator interface instead.
	Iter(func(key interface{}, val Value) bool);
}

type MapValue interface {
	Value;
	Get() Map;
	Set(Map);
}

/*
 * 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;
}

// 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;
}

// The universal scope
func newUniverse() *Scope {
	sc := &Scope{nil, 0};
	sc.block = &block{
		scope: sc,
		defs: make(map[string] Def)
	};
	return sc;
}
var universe *Scope = newUniverse();

/*
 * Frames
 */

type Frame struct {
	Outer *Frame;
	Vars []Value;
}