go/usr/austin/eval/stmt.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";
	"eval";
	"log";
	"os";
	"go/ast";
	"go/scanner";
	"go/token";
	"strconv";
)

/*
 * Statement compiler
 */

type stmtCompiler struct {
	*blockCompiler;
	pos token.Position;
	// err should be initialized to true before visiting and set
	// to false when the statement is compiled successfully.  The
	// function invoking Visit should or this with
	// blockCompiler.err.  This is less error prone than setting
	// blockCompiler.err on every failure path.
	err bool;
}

func (a *stmtCompiler) diag(format string, args ...) {
	a.diagAt(&a.pos, format, args);
}

/*
 * Statement visitors
 */

func (a *stmtCompiler) DoBadStmt(s *ast.BadStmt) {
	// Do nothing.  Already reported by parser.
}

func (a *stmtCompiler) DoDeclStmt(s *ast.DeclStmt) {
	log.Crash("Not implemented");
}

func (a *stmtCompiler) DoEmptyStmt(s *ast.EmptyStmt) {
	a.err = false;
}

func (a *stmtCompiler) DoLabeledStmt(s *ast.LabeledStmt) {
	log.Crash("Not implemented");
}

func (a *stmtCompiler) DoExprStmt(s *ast.ExprStmt) {
	e := a.compileExpr(a.scope, s.X, false);
	if e == nil {
		return;
	}

	if e.exec == nil {
		a.diag("%s cannot be used as expression statement", e.desc);
		return;
	}

	exec := e.exec;
	a.push(func(v *vm) {
		exec(v.f);
	});
	a.err = false;
}

func (a *stmtCompiler) DoIncDecStmt(s *ast.IncDecStmt) {
	l := a.compileExpr(a.scope, s.X, false);
	if l == nil {
		return;
	}

	if l.evalAddr == nil {
		l.diag("cannot assign to %s", l.desc);
		return;
	}
	if !(l.t.isInteger() || l.t.isFloat()) {
		l.diagOpType(s.Tok, l.t);
		return;
	}

	effect, l := l.extractEffect();

	one := l.copy();
	one.pos = s.Pos();
	one.t = IdealIntType;
	one.evalIdealInt = func() *bignum.Integer { return bignum.Int(1) };

	var op token.Token;
	switch s.Tok {
	case token.INC:
		op = token.ADD;
	case token.DEC:
		op = token.SUB;
	default:
		log.Crashf("Unexpected IncDec token %v", s.Tok);
	}

	binop := l.copy();
	binop.pos = s.Pos();
	binop.doBinaryExpr(op, l, one);
	if binop.t == nil {
		return;
	}

	assign := a.compileAssign(s.Pos(), l.t, []*exprCompiler{binop}, "", "");
	if assign == nil {
		log.Crashf("compileAssign type check failed");
	}

	lf := l.evalAddr;
	a.push(func(v *vm) {
		effect(v.f);
		assign(lf(v.f), v.f);
	});
	a.err = false;
}

func (a *stmtCompiler) doAssign(s *ast.AssignStmt) {
	bad := false;

	// Compile right side first so we have the types when
	// compiling the left side and so we don't see definitions
	// made on the left side.
	rs := make([]*exprCompiler, len(s.Rhs));
	for i, re := range s.Rhs {
		rs[i] = a.compileExpr(a.scope, re, false);
		if rs[i] == nil {
			bad = true;
			continue;
		}
	}

	errOp := "assignment";
	if s.Tok == token.DEFINE {
		errOp = "definition";
	}
	ac, ok := a.checkAssign(s.Pos(), rs, "assignment", "value");
	if !ok {
		bad = true;
	}

	// If this is a definition and the LHS is too big, we won't be
	// able to produce the usual error message because we can't
	// begin to infer the types of the LHS.
	if s.Tok == token.DEFINE && len(s.Lhs) > len(ac.rmt.Elems) {
		a.diag("not enough values for definition");
		bad = true;
	}

	// Compile left side
	ls := make([]*exprCompiler, len(s.Lhs));
	nDefs := 0;
	for i, le := range s.Lhs {
		if s.Tok == token.DEFINE {
			// Check that it's an identifier
			ident, ok := le.(*ast.Ident);
			if !ok {
				a.diagAt(le, "left side of := must be a name");
				bad = true;
				// Suppress new defitions errors
				nDefs++;
				continue;
			}

			// Is this simply an assignment?
			if _, ok := a.scope.defs[ident.Value]; ok {
				goto assignment;
			}
			nDefs++;

			// Compute the identifier's type from the RHS
			// type.  We use the computed MultiType so we
			// don't have to worry about unpacking.
			var lt Type;
			switch {
			case i >= len(ac.rmt.Elems):
				// Define a placeholder.  We already
				// gave the "not enough" error above.
				lt = nil;

			case ac.rmt.Elems[i] == nil:
				// We gave the error when we compiled
				// the RHS.
				lt = nil;

			case ac.rmt.Elems[i].isIdeal():
				// If the type is absent and the
				// corresponding expression is a
				// constant expression of ideal
				// integer or ideal float type, the
				// type of the declared variable is
				// int or float respectively.
				switch {
				case ac.rmt.Elems[i].isInteger():
					lt = IntType;
				case ac.rmt.Elems[i].isFloat():
					lt = FloatType;
				default:
					log.Crashf("unexpected ideal type %v", rs[i].t);
				}

			default:
				lt = ac.rmt.Elems[i];
			}

			// Define identifier
			v := a.scope.DefineVar(ident.Value, lt);
			if v == nil {
				log.Crashf("Failed to define %s", ident.Value);
			}
		}

	assignment:
		ls[i] = a.compileExpr(a.scope, le, false);
		if ls[i] == nil {
			bad = true;
			continue;
		}

		if ls[i].evalAddr == nil {
			ls[i].diag("cannot assign to %s", ls[i].desc);
			bad = true;
			continue;
		}
	}

	// A short variable declaration may redeclare variables
	// provided they were originally declared in the same block
	// with the same type, and at least one of the variables is
	// new.
	if s.Tok == token.DEFINE && nDefs == 0 {
		a.diag("at least one new variable must be declared");
		return;
	}

	if bad {
		return;
	}

	// Create assigner
	var lt Type;
	n := len(s.Lhs);
	if n == 1 {
		lt = ls[0].t;
	} else {
		lts := make([]Type, len(ls));
		for i, l := range ls {
			if l != nil {
				lts[i] = l.t;
			}
		}
		lt = NewMultiType(lts);
	}
	assign := ac.compile(lt);
	if assign == nil {
		return;
	}

	// Compile
	if n == 1 {
		// Don't need temporaries and can avoid []Value.
		lf := ls[0].evalAddr;
		a.push(func(v *vm) { assign(lf(v.f), v.f) });
	} else if s.Tok == token.DEFINE && nDefs == n {
		// Don't need temporaries
		lfs := make([]func(*Frame) Value, n);
		for i, l := range ls {
			lfs[i] = l.evalAddr;
		}
		a.push(func(v *vm) {
			dest := make([]Value, n);
			for i, lf := range lfs {
				dest[i] = lf(v.f);
			}
			assign(multiV(dest), v.f);
		});
	} else {
		// Need temporaries
		lmt := lt.(*MultiType);
		lfs := make([]func(*Frame) Value, n);
		for i, l := range ls {
			lfs[i] = l.evalAddr;
		}
		a.push(func(v *vm) {
			temp := lmt.Zero().(multiV);
			assign(temp, v.f);
			// Copy to destination
			for i := 0; i < n; i ++ {
				// TODO(austin) Need to evaluate LHS
				// before RHS
				lfs[i](v.f).Assign(temp[i]);
			}
		});
	}
	a.err = false;
}

var assignOpToOp = map[token.Token] token.Token {
	token.ADD_ASSIGN : token.ADD,
	token.SUB_ASSIGN : token.SUB,
	token.MUL_ASSIGN : token.MUL,
	token.QUO_ASSIGN : token.QUO,
	token.REM_ASSIGN : token.REM,

	token.AND_ASSIGN : token.AND,
	token.OR_ASSIGN  : token.OR,
        token.XOR_ASSIGN : token.XOR,
        token.SHL_ASSIGN : token.SHL,
        token.SHR_ASSIGN : token.SHR,
        token.AND_NOT_ASSIGN : token.AND_NOT,
}

func (a *stmtCompiler) doAssignOp(s *ast.AssignStmt) {
	if len(s.Lhs) != 1 || len(s.Rhs) != 1 {
		a.diag("tuple assignment cannot be combined with an arithmetic operation");
		return;
	}

	l := a.compileExpr(a.scope, s.Lhs[0], false);
	r := a.compileExpr(a.scope, s.Rhs[0], false);
	if l == nil || r == nil {
		return;
	}

	if l.evalAddr == nil {
		l.diag("cannot assign to %s", l.desc);
		return;
	}

	effect, l := l.extractEffect();

	binop := r.copy();
	binop.pos = s.TokPos;
	binop.doBinaryExpr(assignOpToOp[s.Tok], l, r);
	if binop.t == nil {
		return;
	}

	assign := a.compileAssign(s.Pos(), l.t, []*exprCompiler{binop}, "assignment", "value");
	if assign == nil {
		log.Crashf("compileAssign type check failed");
	}

	lf := l.evalAddr;
	a.push(func(v *vm) {
		effect(v.f);
		assign(lf(v.f), v.f);
	});
	a.err = false;
}

func (a *stmtCompiler) DoAssignStmt(s *ast.AssignStmt) {
	switch s.Tok {
	case token.ASSIGN, token.DEFINE:
		a.doAssign(s);

	default:
		a.doAssignOp(s);
	}
}

func (a *stmtCompiler) DoGoStmt(s *ast.GoStmt) {
	log.Crash("Not implemented");
}

func (a *stmtCompiler) DoDeferStmt(s *ast.DeferStmt) {
	log.Crash("Not implemented");
}

func (a *stmtCompiler) DoReturnStmt(s *ast.ReturnStmt) {
	if a.fnType == nil {
		a.diag("cannot return at the top level");
		return;
	}

	// Supress return errors even if we fail to compile this
	// return statement.
	a.returned = true;

	if len(s.Results) == 0 && (len(a.fnType.Out) == 0 || a.outVarsNamed) {
		// Simple case.  Simply exit from the function.
		a.push(func(v *vm) { v.pc = ^uint(0) });
		a.err = false;
		return;
	}

	// Compile expressions
	bad := false;
	rs := make([]*exprCompiler, len(s.Results));
	for i, re := range s.Results {
		rs[i] = a.compileExpr(a.scope, re, false);
		if rs[i] == nil {
			bad = true;
		}
	}
	if bad {
		return;
	}

	// Create assigner

	// However, if the expression list in the "return" statement
	// is a single call to a multi-valued function, the values
	// returned from the called function will be returned from
	// this one.
	assign := a.compileAssign(s.Pos(), NewMultiType(a.fnType.Out), rs, "return", "value");
	if assign == nil {
		return;
	}

	// XXX(Spec) "The result types of the current function and the
	// called function must match."  Match is fuzzy.  It should
	// say that they must be assignment compatible.

	// Compile
	start := len(a.fnType.In);
	nout := len(a.fnType.Out);
	a.push(func(v *vm) {
		assign(multiV(v.activation.Vars[start:start+nout]), v.f);
		v.pc = ^uint(0);
	});
	a.err = false;
}

func (a *stmtCompiler) DoBranchStmt(s *ast.BranchStmt) {
	switch s.Tok {
	case token.BREAK:
		if s.Label != nil {
			log.Crash("break with label not implemented");
		}

		bc := a.blockCompiler;
		for ; bc != nil; bc = bc.parent {
			if bc.breakPC != nil {
				pc := bc.breakPC;
				a.push(func(v *vm) { v.pc = *pc });
				a.err = false;
				return;
			}
		}
		a.diag("break outside for loop, switch, or select");

	case token.CONTINUE:
		if s.Label != nil {
			log.Crash("continue with label not implemented");
		}

		bc := a.blockCompiler;
		for ; bc != nil; bc = bc.parent {
			if bc.continuePC != nil {
				pc := bc.continuePC;
				a.push(func(v *vm) { v.pc = *pc });
				a.err = false;
				return;
			}
		}
		a.diag("continue outside for loop");

	case token.GOTO:
		log.Crash("goto not implemented");

	case token.FALLTHROUGH:
		log.Crash("fallthrough not implemented");

	default:
		log.Crash("Unexpected branch token %v", s.Tok);
	}
}

func (a *stmtCompiler) DoBlockStmt(s *ast.BlockStmt) {
	bc := a.enterChild();
	bc.compileStmts(s);
	bc.exit();

	a.returned = a.returned || bc.returned;
	a.err = false;
}

func (a *stmtCompiler) DoIfStmt(s *ast.IfStmt) {
	// The scope of any variables declared by [the init] statement
	// extends to the end of the "if" statement and the variables
	// are initialized once before the statement is entered.
	//
	// XXX(Spec) What this really wants to say is that there's an
	// implicit scope wrapping every if, for, and switch
	// statement.  This is subtly different from what it actually
	// says when there's a non-block else clause, because that
	// else claus has to execute in a scope that is *not* the
	// surrounding scope.
	bc := a.blockCompiler;
	bc = bc.enterChild();
	defer bc.exit();

	// Compile init statement, if any
	if s.Init != nil {
		bc.compileStmt(s.Init);
	}

	var elsePC, endPC uint;

	// Compile condition, if any.  If there is no condition, we
	// fall through to the body.
	bad := false;
	if s.Cond != nil {
		e := bc.compileExpr(bc.scope, s.Cond, false);
		switch {
		case e == nil:
			bad = true;
		case !e.t.isBoolean():
			e.diag("'if' condition must be boolean\n\t%v", e.t);
			bad = true;
		default:
			eval := e.asBool();
			a.push(func(v *vm) {
				if !eval(v.f) {
					v.pc = elsePC;
				}
			});
		}
	}

	// Compile body
	body := bc.enterChild();
	body.compileStmts(s.Body);
	body.exit();

	// Compile else
	if s.Else != nil {
		// Skip over else if we executed the body
		a.push(func(v *vm) {
			v.pc = endPC;
		});
		elsePC = a.nextPC();
		bc.compileStmt(s.Else);

		if body.returned && bc.returned {
			a.returned = true;
		}
	} else {
		elsePC = a.nextPC();
	}
	endPC = a.nextPC();

	if !bad {
		a.err = false;
	}
}

func (a *stmtCompiler) DoCaseClause(s *ast.CaseClause) {
	log.Crash("Not implemented");
}

func (a *stmtCompiler) DoSwitchStmt(s *ast.SwitchStmt) {
	log.Crash("Not implemented");
}

func (a *stmtCompiler) DoTypeCaseClause(s *ast.TypeCaseClause) {
	log.Crash("Not implemented");
}

func (a *stmtCompiler) DoTypeSwitchStmt(s *ast.TypeSwitchStmt) {
	log.Crash("Not implemented");
}

func (a *stmtCompiler) DoCommClause(s *ast.CommClause) {
	log.Crash("Not implemented");
}

func (a *stmtCompiler) DoSelectStmt(s *ast.SelectStmt) {
	log.Crash("Not implemented");
}

func (a *stmtCompiler) DoForStmt(s *ast.ForStmt) {
	// Compile init statement, if any
	bc := a.blockCompiler;
	if s.Init != nil {
		bc = bc.enterChild();
		defer bc.exit();
		bc.compileStmt(s.Init);
	}

	var bodyPC, postPC, checkPC, endPC uint;

	// Jump to condition check.  We generate slightly less code by
	// placing the condition check after the body.
	a.push(func(v *vm) { v.pc = checkPC });

	// Compile body
	bodyPC = a.nextPC();
	body := bc.enterChild();
	body.breakPC = &endPC;
	body.continuePC = &postPC;
	body.compileStmts(s.Body);
	body.exit();

	// Compile post, if any
	postPC = a.nextPC();
	if s.Post != nil {
		// TODO(austin) Does the parser disallow short
		// declarations in s.Post?
		bc.compileStmt(s.Post);
	}

	// Compile condition check, if any
	bad := false;
	checkPC = a.nextPC();
	if s.Cond == nil {
		// If the condition is absent, it is equivalent to true.
		a.push(func(v *vm) { v.pc = bodyPC });
	} else {
		e := bc.compileExpr(bc.scope, s.Cond, false);
		switch {
		case e == nil:
			bad = true;
		case !e.t.isBoolean():
			a.diag("'for' condition must be boolean\n\t%v", e.t);
			bad = true;
		default:
			eval := e.asBool();
			a.push(func(v *vm) {
				if eval(v.f) {
					v.pc = bodyPC;
				}
			});
		}
	}

	endPC = a.nextPC();

	if !bad {
		a.err = false;
	}
}

func (a *stmtCompiler) DoRangeStmt(s *ast.RangeStmt) {
	log.Crash("Not implemented");
}

/*
 * Block compiler
 */

func (a *blockCompiler) compileStmt(s ast.Stmt) {
	if a.child != nil {
		log.Crash("Child scope still entered");
	}
	sc := &stmtCompiler{a, s.Pos(), true};
	s.Visit(sc);
	if a.child != nil {
		log.Crash("Forgot to exit child scope");
	}
	a.err = a.err || sc.err;
}

func (a *blockCompiler) compileStmts(block *ast.BlockStmt) {
	for i, sub := range block.List {
		a.compileStmt(sub);
	}
}

func (a *blockCompiler) enterChild() *blockCompiler {
	if a.child != nil {
		log.Crash("Failed to exit child block before entering another child");
	}
	blockScope := a.scope.Fork();
	bc := &blockCompiler{
		funcCompiler: a.funcCompiler,
		scope: blockScope,
		returned: false,
		parent: a,
	};
	a.child = bc;
	a.push(func(v *vm) {
		v.f = blockScope.NewFrame(v.f);
	});
	return bc;
}

func (a *blockCompiler) exit() {
	if a.parent == nil {
		log.Crash("Cannot exit top-level block");
	}
	if a.parent.child != a {
		log.Crash("Double exit of block");
	}
	if a.child != nil {
		log.Crash("Exit of parent block without exit of child block");
	}
	a.push(func(v *vm) {
		v.f = v.f.Outer;
	});
	a.parent.child = nil;
}

/*
 * Function compiler
 */

func (a *compiler) compileFunc(scope *Scope, decl *FuncDecl, body *ast.BlockStmt) (func (f *Frame) Func) {
	// Create body scope
	//
	// The scope of a parameter or result is the body of the
	// corresponding function.
	bodyScope := scope.Fork();
	for i, t := range decl.Type.In {
		if decl.InNames[i] != nil {
			bodyScope.DefineVar(decl.InNames[i].Value, t);
		} else {
			// TODO(austin) Not technically a temp
			bodyScope.DefineTemp(t);
		}
	}
	for i, t := range decl.Type.Out {
		if decl.OutNames[i] != nil {
			bodyScope.DefineVar(decl.OutNames[i].Value, t);
		} else {
			bodyScope.DefineTemp(t);
		}
	}

	// Create block context
	fc := &funcCompiler{a, decl.Type, false, newCodeBuf(), false};
	if len(decl.OutNames) > 0 && decl.OutNames[0] != nil {
		fc.outVarsNamed = true;
	}
	bc := &blockCompiler{
		funcCompiler: fc,
		scope: bodyScope,
		returned: false,
	};

	// Compile body
	bc.compileStmts(body);

	// TODO(austin) Check that all gotos were linked?

	if fc.err {
		return nil;
	}

	// Check that the body returned if necessary.  We only check
	// this if there were no errors compiling the body.
	if len(decl.Type.Out) > 0 && !bc.returned {
		// XXX(Spec) Not specified.
		a.diagAt(&body.Rbrace, "function ends without a return statement");
		return nil;
	}

	code := fc.get();
	return func(f *Frame) Func { return &evalFunc{bodyScope, f, code} };
}

/*
 * Testing interface
 */

type Stmt struct {
	f func (f *Frame);
}

func (s *Stmt) Exec(f *Frame) {
	s.f(f);
}

func CompileStmts(scope *Scope, stmts []ast.Stmt) (*Stmt, os.Error) {
	errors := scanner.NewErrorVector();
	cc := &compiler{errors};
	fc := &funcCompiler{cc, nil, false, newCodeBuf(), false};
	bc := &blockCompiler{
		funcCompiler: fc,
		scope: scope,
		returned: false
	};
	out := make([]*Stmt, len(stmts));
	for i, stmt := range stmts {
		bc.compileStmt(stmt);
	}
	if fc.err {
		return nil, errors.GetError(scanner.Sorted);
	}
	code := fc.get();
	return &Stmt{func(f *Frame) { code.exec(f); }}, nil;
}