code review 4314054: go/types: New Go type hierarchy implementation for AST.

src/pkg/go/types/const.go

+// Copyright 2011 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.
+
+// This file implements operations on ideal constants.
+
+package types
+
+import (
+        "big"
+        "go/token"
+        "strconv"
+)
+
+
+// TODO(gri) Consider changing the API so Const is an interface
+//           and operations on consts don't have to type switch.
+
+// A Const implements an ideal constant Value.
+// The zero value z for a Const is not a valid constant value.
+type Const struct {
+        // representation of constant values:
+        // ideal bool     ->  bool
+        // ideal int      ->  *big.Int
+        // ideal float    ->  *big.Rat
+        // ideal complex  ->  cmplx
+        // ideal string   ->  string
+        val interface{}
+}
+
+
+// Representation of complex values.
+type cmplx struct {
+        re, im *big.Rat
+}
+
+
+func assert(cond bool) {
+        if !cond {
+                panic("go/types internal error: assertion failed")
+        }
+}
+
+
+// MakeConst makes an ideal constant from a literal
+// token and the corresponding literal string.
+func MakeConst(tok token.Token, lit string) Const {
+        switch tok {
+        case token.INT:
+                var x big.Int
+                _, ok := x.SetString(lit, 0)
+                assert(ok)
+                return Const{&x}
+        case token.FLOAT:
+                var y big.Rat
+                _, ok := y.SetString(lit)
+                assert(ok)
+                return Const{&y}
+        case token.IMAG:
+                assert(lit[len(lit)-1] == 'i')
+                var im big.Rat
+                _, ok := im.SetString(lit[0 : len(lit)-1])
+                assert(ok)
+                return Const{cmplx{big.NewRat(0, 1), &im}}
+        case token.CHAR:
+                assert(lit[0] == '\'' && lit[len(lit)-1] == '\'')
+                code, _, _, err := strconv.UnquoteChar(lit[1:len(lit)-1], '\'')
+                assert(err == nil)
+                return Const{big.NewInt(int64(code))}
+        case token.STRING:
+                s, err := strconv.Unquote(lit)
+                assert(err == nil)
+                return Const{s}
+        }
+        panic("unreachable")
+}
+
+
+// MakeZero returns the zero constant for the given type.
+func MakeZero(typ *Type) Const {
+        // TODO(gri) fix this
+        return Const{0}
+}
+
+
+// Match attempts to match the internal constant representations of x and y.
+// If the attempt is successful, the result is the values of x and y,
+// if necessary converted to have the same internal representation; otherwise
+// the results are invalid.
+func (x Const) Match(y Const) (u, v Const) {
+        switch a := x.val.(type) {
+        case bool:
+                if _, ok := y.val.(bool); ok {
+                        u, v = x, y
+                }
+        case *big.Int:
+                switch y.val.(type) {
+                case *big.Int:
+                        u, v = x, y
+                case *big.Rat:
+                        var z big.Rat
+                        z.SetInt(a)
+                        u, v = Const{&z}, y
+                case cmplx:
+                        var z big.Rat
+                        z.SetInt(a)
+                        u, v = Const{cmplx{&z, big.NewRat(0, 1)}}, y
+                }
+        case *big.Rat:
+                switch y.val.(type) {
+                case *big.Int:
+                        v, u = y.Match(x)
+                case *big.Rat:
+                        u, v = x, y
+                case cmplx:
+                        u, v = Const{cmplx{a, big.NewRat(0, 0)}}, y
+                }
+        case cmplx:
+                switch y.val.(type) {
+                case *big.Int, *big.Rat:
+                        v, u = y.Match(x)
+                case cmplx:
+                        u, v = x, y
+                }
+        case string:
+                if _, ok := y.val.(string); ok {
+                        u, v = x, y
+                }
+        default:
+                panic("unreachable")
+        }
+        return
+}
+
+
+// Convert attempts to convert the constant x to a given type.
+// If the attempt is successful, the result is the new constant;
+// otherwise the result is invalid.
+func (x Const) Convert(typ *Type) Const {
+        // TODO(gri) implement this
+        switch x := x.val.(type) {
+        case bool:
+        case *big.Int:
+        case *big.Rat:
+        case cmplx:
+        case string:
+        }
+        return x
+}
+
+
+func (x Const) String() string {
+        switch x := x.val.(type) {
+        case bool:
+                if x {
+                        return "true"
+                }
+                return "false"
+        case *big.Int:
+                return x.String()
+        case *big.Rat:
+                return x.FloatString(10) // 10 digits of precision after decimal point seems fine
+        case cmplx:
+                // TODO(gri) don't print 0 components
+                return x.re.FloatString(10) + " + " + x.im.FloatString(10) + "i"
+        case string:
+                return x
+        }
+        panic("unreachable")
+}
+
+
+func (x Const) UnaryOp(op token.Token) Const {
+        panic("unimplemented")
+}
+
+
+func (x Const) BinaryOp(op token.Token, y Const) Const {
+        var z interface{}
+        switch x := x.val.(type) {
+        case bool:
+                z = binaryBoolOp(x, op, y.val.(bool))
+        case *big.Int:
+                z = binaryIntOp(x, op, y.val.(*big.Int))
+        case *big.Rat:
+                z = binaryFloatOp(x, op, y.val.(*big.Rat))
+        case cmplx:
+                z = binaryCmplxOp(x, op, y.val.(cmplx))
+        case string:
+                z = binaryStringOp(x, op, y.val.(string))
+        default:
+                panic("unreachable")
+        }
+        return Const{z}
+}
+
+
+func binaryBoolOp(x bool, op token.Token, y bool) interface{} {
+        switch op {
+        case token.EQL:
+                return x == y
+        case token.NEQ:
+                return x != y
+        }
+        panic("unreachable")
+}
+
+
+func binaryIntOp(x *big.Int, op token.Token, y *big.Int) interface{} {
+        var z big.Int
+        switch op {
+        case token.ADD:
+                return z.Add(x, y)
+        case token.SUB:
+                return z.Sub(x, y)
+        case token.MUL:
+                return z.Mul(x, y)
+        case token.QUO:
+                return z.Quo(x, y)
+        case token.REM:
+                return z.Rem(x, y)
+        case token.AND:
+                return z.And(x, y)
+        case token.OR:
+                return z.Or(x, y)
+        case token.XOR:
+                return z.Xor(x, y)
+        case token.AND_NOT:
+                return z.AndNot(x, y)
+        case token.SHL:
+                panic("unimplemented")
+        case token.SHR:
+                panic("unimplemented")
+        case token.EQL:
+                return x.Cmp(y) == 0
+        case token.NEQ:
+                return x.Cmp(y) != 0
+        case token.LSS:
+                return x.Cmp(y) < 0
+        case token.LEQ:
+                return x.Cmp(y) <= 0
+        case token.GTR:
+                return x.Cmp(y) > 0
+        case token.GEQ:
+                return x.Cmp(y) >= 0
+        }
+        panic("unreachable")
+}
+
+
+func binaryFloatOp(x *big.Rat, op token.Token, y *big.Rat) interface{} {
+        var z big.Rat
+        switch op {
+        case token.ADD:
+                return z.Add(x, y)
+        case token.SUB:
+                return z.Sub(x, y)
+        case token.MUL:
+                return z.Mul(x, y)
+        case token.QUO:
+                return z.Quo(x, y)
+        case token.EQL:
+                return x.Cmp(y) == 0
+        case token.NEQ:
+                return x.Cmp(y) != 0
+        case token.LSS:
+                return x.Cmp(y) < 0
+        case token.LEQ:
+                return x.Cmp(y) <= 0
+        case token.GTR:
+                return x.Cmp(y) > 0
+        case token.GEQ:
+                return x.Cmp(y) >= 0
+        }
+        panic("unreachable")
+}
+
+
+func binaryCmplxOp(x cmplx, op token.Token, y cmplx) interface{} {
+        a, b := x.re, x.im
+        c, d := y.re, y.im
+        switch op {
+        case token.ADD:
+                // (a+c) + i(b+d)
+                var re, im big.Rat
+                re.Add(a, c)
+                im.Add(b, d)
+                return cmplx{&re, &im}
+        case token.SUB:
+                // (a-c) + i(b-d)
+                var re, im big.Rat
+                re.Sub(a, c)
+                im.Sub(b, d)
+                return cmplx{&re, &im}
+        case token.MUL:
+                // (ac-bd) + i(bc+ad)
+                var ac, bd, bc, ad big.Rat
+                ac.Mul(a, c)
+                bd.Mul(b, d)
+                bc.Mul(b, c)
+                ad.Mul(a, d)
+                var re, im big.Rat
+                re.Sub(&ac, &bd)
+                im.Add(&bc, &ad)
+                return cmplx{&re, &im}
+        case token.QUO:
+                // (ac+bd)/s + i(bc-ad)/s, with s = cc + dd
+                var ac, bd, bc, ad, s big.Rat
+                ac.Mul(a, c)
+                bd.Mul(b, d)
+                bc.Mul(b, c)
+                ad.Mul(a, d)
+                s.Add(c.Mul(c, c), d.Mul(d, d))
+                var re, im big.Rat
+                re.Add(&ac, &bd)
+                re.Quo(&re, &s)
+                im.Sub(&bc, &ad)
+                im.Quo(&im, &s)
+                return cmplx{&re, &im}
+        case token.EQL:
+                return a.Cmp(c) == 0 && b.Cmp(d) == 0
+        case token.NEQ:
+                return a.Cmp(c) != 0 || b.Cmp(d) != 0
+        }
+        panic("unreachable")
+}
+
+
+func binaryStringOp(x string, op token.Token, y string) interface{} {
+        switch op {
+        case token.ADD:
+                return x + y
+        case token.EQL:
+                return x == y
+        case token.NEQ:
+                return x != y
+        case token.LSS:
+                return x < y
+        case token.LEQ:
+                return x <= y
+        case token.GTR:
+                return x > y
+        case token.GEQ:
+                return x >= y
+        }
+        panic("unreachable")
+}