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eval.go
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eval.go
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// Copyright 2017 The Bazel 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 starlark
import (
"fmt"
"io"
"log"
"math/big"
"math/bits"
"sort"
"strings"
"sync/atomic"
"time"
"unicode"
"unicode/utf8"
"unsafe"
"go.starlark.net/internal/compile"
"go.starlark.net/internal/spell"
"go.starlark.net/resolve"
"go.starlark.net/syntax"
)
// A Thread contains the state of a Starlark thread,
// such as its call stack and thread-local storage.
// The Thread is threaded throughout the evaluator.
type Thread struct {
// Name is an optional name that describes the thread, for debugging.
Name string
// stack is the stack of (internal) call frames.
stack []*frame
// Print is the client-supplied implementation of the Starlark
// 'print' function. If nil, fmt.Fprintln(os.Stderr, msg) is
// used instead.
Print func(thread *Thread, msg string)
// Load is the client-supplied implementation of module loading.
// Repeated calls with the same module name must return the same
// module environment or error.
// The error message need not include the module name.
//
// See example_test.go for some example implementations of Load.
Load func(thread *Thread, module string) (StringDict, error)
// OnMaxSteps is called when the thread reaches the limit set by SetMaxExecutionSteps.
// The default behavior is to call thread.Cancel("too many steps").
OnMaxSteps func(thread *Thread)
// Steps a count of abstract computation steps executed
// by this thread. It is incremented by the interpreter. It may be used
// as a measure of the approximate cost of Starlark execution, by
// computing the difference in its value before and after a computation.
//
// The precise meaning of "step" is not specified and may change.
Steps, maxSteps uint64
// cancelReason records the reason from the first call to Cancel.
cancelReason *string
// locals holds arbitrary "thread-local" Go values belonging to the client.
// They are accessible to the client but not to any Starlark program.
locals map[string]interface{}
// proftime holds the accumulated execution time since the last profile event.
proftime time.Duration
}
// ExecutionSteps returns the current value of Steps.
func (thread *Thread) ExecutionSteps() uint64 {
return thread.Steps
}
// SetMaxExecutionSteps sets a limit on the number of Starlark
// computation steps that may be executed by this thread. If the
// thread's step counter exceeds this limit, the interpreter calls
// the optional OnMaxSteps function or the default behavior
// of calling thread.Cancel("too many steps").
func (thread *Thread) SetMaxExecutionSteps(max uint64) {
thread.maxSteps = max
}
// Uncancel resets the cancellation state.
//
// Unlike most methods of Thread, it is safe to call Uncancel from any
// goroutine, even if the thread is actively executing.
func (thread *Thread) Uncancel() {
atomic.StorePointer((*unsafe.Pointer)(unsafe.Pointer(&thread.cancelReason)), nil)
}
// Cancel causes execution of Starlark code in the specified thread to
// promptly fail with an EvalError that includes the specified reason.
// There may be a delay before the interpreter observes the cancellation
// if the thread is currently in a call to a built-in function.
//
// Call [Uncancel] to reset the cancellation state.
//
// Unlike most methods of Thread, it is safe to call Cancel from any
// goroutine, even if the thread is actively executing.
func (thread *Thread) Cancel(reason string) {
// Atomically set cancelReason, preserving earlier reason if any.
atomic.CompareAndSwapPointer((*unsafe.Pointer)(unsafe.Pointer(&thread.cancelReason)), nil, unsafe.Pointer(&reason))
}
// SetLocal sets the thread-local value associated with the specified key.
// It must not be called after execution begins.
func (thread *Thread) SetLocal(key string, value interface{}) {
if thread.locals == nil {
thread.locals = make(map[string]interface{})
}
thread.locals[key] = value
}
// Local returns the thread-local value associated with the specified key.
func (thread *Thread) Local(key string) interface{} {
return thread.locals[key]
}
// CallFrame returns a copy of the specified frame of the callstack.
// It should only be used in built-ins called from Starlark code.
// Depth 0 means the frame of the built-in itself, 1 is its caller, and so on.
//
// It is equivalent to CallStack().At(depth), but more efficient.
func (thread *Thread) CallFrame(depth int) CallFrame {
return thread.frameAt(depth).asCallFrame()
}
func (thread *Thread) frameAt(depth int) *frame {
return thread.stack[len(thread.stack)-1-depth]
}
// CallStack returns a new slice containing the thread's stack of call frames.
func (thread *Thread) CallStack() CallStack {
frames := make([]CallFrame, len(thread.stack))
for i, fr := range thread.stack {
frames[i] = fr.asCallFrame()
}
return frames
}
// CallStackDepth returns the number of frames in the current call stack.
func (thread *Thread) CallStackDepth() int { return len(thread.stack) }
// A StringDict is a mapping from names to values, and represents
// an environment such as the global variables of a module.
// It is not a true starlark.Value.
type StringDict map[string]Value
// Keys returns a new sorted slice of d's keys.
func (d StringDict) Keys() []string {
names := make([]string, 0, len(d))
for name := range d {
names = append(names, name)
}
sort.Strings(names)
return names
}
func (d StringDict) String() string {
buf := new(strings.Builder)
buf.WriteByte('{')
sep := ""
for _, name := range d.Keys() {
buf.WriteString(sep)
buf.WriteString(name)
buf.WriteString(": ")
writeValue(buf, d[name], nil)
sep = ", "
}
buf.WriteByte('}')
return buf.String()
}
func (d StringDict) Freeze() {
for _, v := range d {
v.Freeze()
}
}
// Has reports whether the dictionary contains the specified key.
func (d StringDict) Has(key string) bool { _, ok := d[key]; return ok }
// A frame records a call to a Starlark function (including module toplevel)
// or a built-in function or method.
type frame struct {
callable Callable // current function (or toplevel) or built-in
pc uint32 // program counter (Starlark frames only)
locals []Value // local variables (Starlark frames only)
spanStart int64 // start time of current profiler span
}
// Position returns the source position of the current point of execution in this frame.
func (fr *frame) Position() syntax.Position {
switch c := fr.callable.(type) {
case *Function:
// Starlark function
return c.funcode.Position(fr.pc)
case callableWithPosition:
// If a built-in Callable defines
// a Position method, use it.
return c.Position()
}
return syntax.MakePosition(&builtinFilename, 0, 0)
}
var builtinFilename = "<builtin>"
// Function returns the frame's function or built-in.
func (fr *frame) Callable() Callable { return fr.callable }
// A CallStack is a stack of call frames, outermost first.
type CallStack []CallFrame
// At returns a copy of the frame at depth i.
// At(0) returns the topmost frame.
func (stack CallStack) At(i int) CallFrame { return stack[len(stack)-1-i] }
// Pop removes and returns the topmost frame.
func (stack *CallStack) Pop() CallFrame {
last := len(*stack) - 1
top := (*stack)[last]
*stack = (*stack)[:last]
return top
}
// String returns a user-friendly description of the stack.
func (stack CallStack) String() string {
out := new(strings.Builder)
if len(stack) > 0 {
fmt.Fprintf(out, "Traceback (most recent call last):\n")
}
for _, fr := range stack {
fmt.Fprintf(out, " %s: in %s\n", fr.Pos, fr.Name)
}
return out.String()
}
// An EvalError is a Starlark evaluation error and
// a copy of the thread's stack at the moment of the error.
type EvalError struct {
Msg string
CallStack CallStack
cause error
}
// A CallFrame represents the function name and current
// position of execution of an enclosing call frame.
type CallFrame struct {
Name string
Pos syntax.Position
}
func (fr *frame) asCallFrame() CallFrame {
return CallFrame{
Name: fr.Callable().Name(),
Pos: fr.Position(),
}
}
func (thread *Thread) evalError(err error) *EvalError {
return &EvalError{
Msg: err.Error(),
CallStack: thread.CallStack(),
cause: err,
}
}
func (e *EvalError) Error() string { return e.Msg }
// Backtrace returns a user-friendly error message describing the stack
// of calls that led to this error.
func (e *EvalError) Backtrace() string {
// If the topmost stack frame is a built-in function,
// remove it from the stack and add print "Error in fn:".
stack := e.CallStack
suffix := ""
if last := len(stack) - 1; last >= 0 && stack[last].Pos.Filename() == builtinFilename {
suffix = " in " + stack[last].Name
stack = stack[:last]
}
return fmt.Sprintf("%sError%s: %s", stack, suffix, e.Msg)
}
func (e *EvalError) Unwrap() error { return e.cause }
// A Program is a compiled Starlark program.
//
// Programs are immutable, and contain no Values.
// A Program may be created by parsing a source file (see SourceProgram)
// or by loading a previously saved compiled program (see CompiledProgram).
type Program struct {
compiled *compile.Program
}
// CompilerVersion is the version number of the protocol for compiled
// files. Applications must not run programs compiled by one version
// with an interpreter at another version, and should thus incorporate
// the compiler version into the cache key when reusing compiled code.
const CompilerVersion = compile.Version
// Filename returns the name of the file from which this program was loaded.
func (prog *Program) Filename() string { return prog.compiled.Toplevel.Pos.Filename() }
func (prog *Program) String() string { return prog.Filename() }
// NumLoads returns the number of load statements in the compiled program.
func (prog *Program) NumLoads() int { return len(prog.compiled.Loads) }
// Load(i) returns the name and position of the i'th module directly
// loaded by this one, where 0 <= i < NumLoads().
// The name is unresolved---exactly as it appears in the source.
func (prog *Program) Load(i int) (string, syntax.Position) {
id := prog.compiled.Loads[i]
return id.Name, id.Pos
}
// WriteTo writes the compiled module to the specified output stream.
func (prog *Program) Write(out io.Writer) error {
data := prog.compiled.Encode()
_, err := out.Write(data)
return err
}
// ExecFile calls [ExecFileOptions] using [syntax.LegacyFileOptions].
//
// Deprecated: use [ExecFileOptions] with [syntax.FileOptions] instead,
// because this function relies on legacy global variables.
func ExecFile(thread *Thread, filename string, src interface{}, predeclared StringDict) (StringDict, error) {
return ExecFileOptions(syntax.LegacyFileOptions(), thread, filename, src, predeclared)
}
// ExecFileOptions parses, resolves, and executes a Starlark file in the
// specified global environment, which may be modified during execution.
//
// Thread is the state associated with the Starlark thread.
//
// The filename and src parameters are as for syntax.Parse:
// filename is the name of the file to execute,
// and the name that appears in error messages;
// src is an optional source of bytes to use
// instead of filename.
//
// predeclared defines the predeclared names specific to this module.
// Execution does not modify this dictionary, though it may mutate
// its values.
//
// If ExecFileOptions fails during evaluation, it returns an *EvalError
// containing a backtrace.
func ExecFileOptions(opts *syntax.FileOptions, thread *Thread, filename string, src interface{}, predeclared StringDict) (StringDict, error) {
// Parse, resolve, and compile a Starlark source file.
_, mod, err := SourceProgramOptions(opts, filename, src, predeclared.Has)
if err != nil {
return nil, err
}
g, err := mod.Init(thread, predeclared)
g.Freeze()
return g, err
}
// SourceProgram calls [SourceProgramOptions] using [syntax.LegacyFileOptions].
//
// Deprecated: use [SourceProgramOptions] with [syntax.FileOptions] instead,
// because this function relies on legacy global variables.
func SourceProgram(filename string, src interface{}, isPredeclared func(string) bool) (*syntax.File, *Program, error) {
return SourceProgramOptions(syntax.LegacyFileOptions(), filename, src, isPredeclared)
}
// SourceProgramOptions produces a new program by parsing, resolving,
// and compiling a Starlark source file.
// On success, it returns the parsed file and the compiled program.
// The filename and src parameters are as for syntax.Parse.
//
// The isPredeclared predicate reports whether a name is
// a pre-declared identifier of the current module.
// Its typical value is predeclared.Has,
// where predeclared is a StringDict of pre-declared values.
func SourceProgramOptions(opts *syntax.FileOptions, filename string, src interface{}, isPredeclared func(string) bool) (*syntax.File, *Program, error) {
f, err := opts.Parse(filename, src, 0)
if err != nil {
return nil, nil, err
}
prog, err := FileProgram(f, isPredeclared)
return f, prog, err
}
// FileProgram produces a new program by resolving,
// and compiling the Starlark source file syntax tree.
// On success, it returns the compiled program.
//
// Resolving a syntax tree mutates it.
// Do not call FileProgram more than once on the same file.
//
// The isPredeclared predicate reports whether a name is
// a pre-declared identifier of the current module.
// Its typical value is predeclared.Has,
// where predeclared is a StringDict of pre-declared values.
func FileProgram(f *syntax.File, isPredeclared func(string) bool) (*Program, error) {
if err := resolve.File(f, isPredeclared, Universe.Has); err != nil {
return nil, err
}
var pos syntax.Position
if len(f.Stmts) > 0 {
pos = syntax.Start(f.Stmts[0])
} else {
pos = syntax.MakePosition(&f.Path, 1, 1)
}
module := f.Module.(*resolve.Module)
compiled := compile.File(f.Options, f.Stmts, pos, "<toplevel>", module.Locals, module.Globals)
return &Program{compiled}, nil
}
// CompiledProgram produces a new program from the representation
// of a compiled program previously saved by Program.Write.
func CompiledProgram(in io.Reader) (*Program, error) {
data, err := io.ReadAll(in)
if err != nil {
return nil, err
}
compiled, err := compile.DecodeProgram(data)
if err != nil {
return nil, err
}
return &Program{compiled}, nil
}
// Init creates a set of global variables for the program,
// executes the toplevel code of the specified program,
// and returns a new, unfrozen dictionary of the globals.
func (prog *Program) Init(thread *Thread, predeclared StringDict) (StringDict, error) {
toplevel := makeToplevelFunction(prog.compiled, predeclared)
_, err := Call(thread, toplevel, nil, nil)
// Convert the global environment to a map.
// We return a (partial) map even in case of error.
return toplevel.Globals(), err
}
// ExecREPLChunk compiles and executes file f in the specified thread
// and global environment. This is a variant of ExecFile specialized to
// the needs of a REPL, in which a sequence of input chunks, each
// syntactically a File, manipulates the same set of module globals,
// which are not frozen after execution.
//
// This function is intended to support only go.starlark.net/repl.
// Its API stability is not guaranteed.
func ExecREPLChunk(f *syntax.File, thread *Thread, globals StringDict) error {
var predeclared StringDict
// -- variant of FileProgram --
if err := resolve.REPLChunk(f, globals.Has, predeclared.Has, Universe.Has); err != nil {
return err
}
var pos syntax.Position
if len(f.Stmts) > 0 {
pos = syntax.Start(f.Stmts[0])
} else {
pos = syntax.MakePosition(&f.Path, 1, 1)
}
module := f.Module.(*resolve.Module)
compiled := compile.File(f.Options, f.Stmts, pos, "<toplevel>", module.Locals, module.Globals)
prog := &Program{compiled}
// -- variant of Program.Init --
toplevel := makeToplevelFunction(prog.compiled, predeclared)
// Initialize module globals from parameter.
for i, id := range prog.compiled.Globals {
if v := globals[id.Name]; v != nil {
toplevel.module.globals[i] = v
}
}
_, err := Call(thread, toplevel, nil, nil)
// Reflect changes to globals back to parameter, even after an error.
for i, id := range prog.compiled.Globals {
if v := toplevel.module.globals[i]; v != nil {
globals[id.Name] = v
}
}
return err
}
func makeToplevelFunction(prog *compile.Program, predeclared StringDict) *Function {
// Create the Starlark value denoted by each program constant c.
constants := make([]Value, len(prog.Constants))
for i, c := range prog.Constants {
var v Value
switch c := c.(type) {
case int64:
v = MakeInt64(c)
case *big.Int:
v = MakeBigInt(c)
case string:
v = String(c)
case compile.Bytes:
v = Bytes(c)
case float64:
v = Float(c)
default:
log.Panicf("unexpected constant %T: %v", c, c)
}
constants[i] = v
}
return &Function{
funcode: prog.Toplevel,
module: &module{
program: prog,
predeclared: predeclared,
globals: make([]Value, len(prog.Globals)),
constants: constants,
},
}
}
// Eval calls [EvalOptions] using [syntax.LegacyFileOptions].
//
// Deprecated: use [EvalOptions] with [syntax.FileOptions] instead,
// because this function relies on legacy global variables.
func Eval(thread *Thread, filename string, src interface{}, env StringDict) (Value, error) {
return EvalOptions(syntax.LegacyFileOptions(), thread, filename, src, env)
}
// EvalOptions parses, resolves, and evaluates an expression within the
// specified (predeclared) environment.
//
// Evaluation cannot mutate the environment dictionary itself,
// though it may modify variables reachable from the dictionary.
//
// The filename and src parameters are as for syntax.Parse.
//
// If EvalOptions fails during evaluation, it returns an *EvalError
// containing a backtrace.
func EvalOptions(opts *syntax.FileOptions, thread *Thread, filename string, src interface{}, env StringDict) (Value, error) {
expr, err := opts.ParseExpr(filename, src, 0)
if err != nil {
return nil, err
}
f, err := makeExprFunc(opts, expr, env)
if err != nil {
return nil, err
}
return Call(thread, f, nil, nil)
}
// EvalExpr calls [EvalExprOptions] using [syntax.LegacyFileOptions].
//
// Deprecated: use [EvalExprOptions] with [syntax.FileOptions] instead,
// because this function relies on legacy global variables.
func EvalExpr(thread *Thread, expr syntax.Expr, env StringDict) (Value, error) {
return EvalExprOptions(syntax.LegacyFileOptions(), thread, expr, env)
}
// EvalExprOptions resolves and evaluates an expression within the
// specified (predeclared) environment.
// Evaluating a comma-separated list of expressions yields a tuple value.
//
// Resolving an expression mutates it.
// Do not call EvalExprOptions more than once for the same expression.
//
// Evaluation cannot mutate the environment dictionary itself,
// though it may modify variables reachable from the dictionary.
//
// If EvalExprOptions fails during evaluation, it returns an *EvalError
// containing a backtrace.
func EvalExprOptions(opts *syntax.FileOptions, thread *Thread, expr syntax.Expr, env StringDict) (Value, error) {
fn, err := makeExprFunc(opts, expr, env)
if err != nil {
return nil, err
}
return Call(thread, fn, nil, nil)
}
// ExprFunc calls [ExprFuncOptions] using [syntax.LegacyFileOptions].
//
// Deprecated: use [ExprFuncOptions] with [syntax.FileOptions] instead,
// because this function relies on legacy global variables.
func ExprFunc(filename string, src interface{}, env StringDict) (*Function, error) {
return ExprFuncOptions(syntax.LegacyFileOptions(), filename, src, env)
}
// ExprFunc returns a no-argument function
// that evaluates the expression whose source is src.
func ExprFuncOptions(options *syntax.FileOptions, filename string, src interface{}, env StringDict) (*Function, error) {
expr, err := options.ParseExpr(filename, src, 0)
if err != nil {
return nil, err
}
return makeExprFunc(options, expr, env)
}
// makeExprFunc returns a no-argument function whose body is expr.
// The options must be consistent with those used when parsing expr.
func makeExprFunc(opts *syntax.FileOptions, expr syntax.Expr, env StringDict) (*Function, error) {
locals, err := resolve.ExprOptions(opts, expr, env.Has, Universe.Has)
if err != nil {
return nil, err
}
return makeToplevelFunction(compile.Expr(opts, expr, "<expr>", locals), env), nil
}
// The following functions are primitive operations of the byte code interpreter.
// list += iterable
func listExtend(x *List, y Iterable) {
if ylist, ok := y.(*List); ok {
// fast path: list += list
x.elems = append(x.elems, ylist.elems...)
} else {
iter := y.Iterate()
defer iter.Done()
var z Value
for iter.Next(&z) {
x.elems = append(x.elems, z)
}
}
}
// getAttr implements x.dot.
func getAttr(x Value, name string) (Value, error) {
hasAttr, ok := x.(HasAttrs)
if !ok {
return nil, fmt.Errorf("%s has no .%s field or method", x.Type(), name)
}
var errmsg string
v, err := hasAttr.Attr(name)
if err == nil {
if v != nil {
return v, nil // success
}
// (nil, nil) => generic error
errmsg = fmt.Sprintf("%s has no .%s field or method", x.Type(), name)
} else if nsa, ok := err.(NoSuchAttrError); ok {
errmsg = string(nsa)
} else {
return nil, err // return error as is
}
// add spelling hint
if n := spell.Nearest(name, hasAttr.AttrNames()); n != "" {
errmsg = fmt.Sprintf("%s (did you mean .%s?)", errmsg, n)
}
return nil, fmt.Errorf("%s", errmsg)
}
// setField implements x.name = y.
func setField(x Value, name string, y Value) error {
if x, ok := x.(HasSetField); ok {
err := x.SetField(name, y)
if _, ok := err.(NoSuchAttrError); ok {
// No such field: check spelling.
if n := spell.Nearest(name, x.AttrNames()); n != "" {
err = fmt.Errorf("%s (did you mean .%s?)", err, n)
}
}
return err
}
return fmt.Errorf("can't assign to .%s field of %s", name, x.Type())
}
// getIndex implements x[y].
func getIndex(x, y Value) (Value, error) {
switch x := x.(type) {
case Mapping: // dict
z, found, err := x.Get(y)
if err != nil {
return nil, err
}
if !found {
return nil, fmt.Errorf("key %v not in %s", y, x.Type())
}
return z, nil
case Indexable: // string, list, tuple
n := x.Len()
i, err := AsInt32(y)
if err != nil {
return nil, fmt.Errorf("%s index: %s", x.Type(), err)
}
origI := i
if i < 0 {
i += n
}
if i < 0 || i >= n {
return nil, outOfRange(origI, n, x)
}
return x.Index(i), nil
}
return nil, fmt.Errorf("unhandled index operation %s[%s]", x.Type(), y.Type())
}
func outOfRange(i, n int, x Value) error {
if n == 0 {
return fmt.Errorf("index %d out of range: empty %s", i, x.Type())
} else {
return fmt.Errorf("%s index %d out of range [%d:%d]", x.Type(), i, -n, n-1)
}
}
// setIndex implements x[y] = z.
func setIndex(x, y, z Value) error {
switch x := x.(type) {
case HasSetKey:
if err := x.SetKey(y, z); err != nil {
return err
}
case HasSetIndex:
n := x.Len()
i, err := AsInt32(y)
if err != nil {
return err
}
origI := i
if i < 0 {
i += n
}
if i < 0 || i >= n {
return outOfRange(origI, n, x)
}
return x.SetIndex(i, z)
default:
return fmt.Errorf("%s value does not support item assignment", x.Type())
}
return nil
}
// Unary applies a unary operator (+, -, ~, not) to its operand.
func Unary(op syntax.Token, x Value) (Value, error) {
// The NOT operator is not customizable.
if op == syntax.NOT {
return !x.Truth(), nil
}
// Int, Float, and user-defined types
if x, ok := x.(HasUnary); ok {
// (nil, nil) => unhandled
y, err := x.Unary(op)
if y != nil || err != nil {
return y, err
}
}
return nil, fmt.Errorf("unknown unary op: %s %s", op, x.Type())
}
// Binary applies a strict binary operator (not AND or OR) to its operands.
// For equality tests or ordered comparisons, use Compare instead.
func Binary(op syntax.Token, x, y Value) (Value, error) {
switch op {
case syntax.PLUS:
switch x := x.(type) {
case String:
if y, ok := y.(String); ok {
return x + y, nil
}
case Int:
switch y := y.(type) {
case Int:
return x.Add(y), nil
case Float:
xf, err := x.finiteFloat()
if err != nil {
return nil, err
}
return xf + y, nil
}
case Float:
switch y := y.(type) {
case Float:
return x + y, nil
case Int:
yf, err := y.finiteFloat()
if err != nil {
return nil, err
}
return x + yf, nil
}
case *List:
if y, ok := y.(*List); ok {
z := make([]Value, 0, x.Len()+y.Len())
z = append(z, x.elems...)
z = append(z, y.elems...)
return NewList(z), nil
}
case Tuple:
if y, ok := y.(Tuple); ok {
z := make(Tuple, 0, len(x)+len(y))
z = append(z, x...)
z = append(z, y...)
return z, nil
}
}
case syntax.MINUS:
switch x := x.(type) {
case Int:
switch y := y.(type) {
case Int:
return x.Sub(y), nil
case Float:
xf, err := x.finiteFloat()
if err != nil {
return nil, err
}
return xf - y, nil
}
case Float:
switch y := y.(type) {
case Float:
return x - y, nil
case Int:
yf, err := y.finiteFloat()
if err != nil {
return nil, err
}
return x - yf, nil
}
case *Set: // difference
if y, ok := y.(*Set); ok {
iter := y.Iterate()
defer iter.Done()
return x.Difference(iter)
}
}
case syntax.STAR:
switch x := x.(type) {
case Int:
switch y := y.(type) {
case Int:
return x.Mul(y), nil
case Float:
xf, err := x.finiteFloat()
if err != nil {
return nil, err
}
return xf * y, nil
case String:
return stringRepeat(y, x)
case Bytes:
return bytesRepeat(y, x)
case *List:
elems, err := tupleRepeat(Tuple(y.elems), x)
if err != nil {
return nil, err
}
return NewList(elems), nil
case Tuple:
return tupleRepeat(y, x)
}
case Float:
switch y := y.(type) {
case Float:
return x * y, nil
case Int:
yf, err := y.finiteFloat()
if err != nil {
return nil, err
}
return x * yf, nil
}
case String:
if y, ok := y.(Int); ok {
return stringRepeat(x, y)
}
case Bytes:
if y, ok := y.(Int); ok {
return bytesRepeat(x, y)
}
case *List:
if y, ok := y.(Int); ok {
elems, err := tupleRepeat(Tuple(x.elems), y)
if err != nil {
return nil, err
}
return NewList(elems), nil
}
case Tuple:
if y, ok := y.(Int); ok {
return tupleRepeat(x, y)
}
}
case syntax.SLASH:
switch x := x.(type) {
case Int:
xf, err := x.finiteFloat()
if err != nil {
return nil, err
}
switch y := y.(type) {
case Int:
yf, err := y.finiteFloat()
if err != nil {
return nil, err
}
if yf == 0.0 {
return nil, fmt.Errorf("floating-point division by zero")
}
return xf / yf, nil
case Float:
if y == 0.0 {
return nil, fmt.Errorf("floating-point division by zero")
}
return xf / y, nil
}
case Float:
switch y := y.(type) {
case Float:
if y == 0.0 {
return nil, fmt.Errorf("floating-point division by zero")
}
return x / y, nil
case Int:
yf, err := y.finiteFloat()
if err != nil {
return nil, err
}
if yf == 0.0 {
return nil, fmt.Errorf("floating-point division by zero")
}
return x / yf, nil
}
}
case syntax.SLASHSLASH:
switch x := x.(type) {
case Int:
switch y := y.(type) {
case Int:
if y.Sign() == 0 {
return nil, fmt.Errorf("floored division by zero")
}
return x.Div(y), nil
case Float:
xf, err := x.finiteFloat()
if err != nil {
return nil, err
}
if y == 0.0 {
return nil, fmt.Errorf("floored division by zero")
}
return floor(xf / y), nil
}
case Float:
switch y := y.(type) {
case Float:
if y == 0.0 {
return nil, fmt.Errorf("floored division by zero")
}
return floor(x / y), nil
case Int:
yf, err := y.finiteFloat()
if err != nil {
return nil, err
}
if yf == 0.0 {
return nil, fmt.Errorf("floored division by zero")
}
return floor(x / yf), nil
}
}
case syntax.PERCENT:
switch x := x.(type) {
case Int:
switch y := y.(type) {
case Int:
if y.Sign() == 0 {
return nil, fmt.Errorf("integer modulo by zero")
}
return x.Mod(y), nil
case Float:
xf, err := x.finiteFloat()
if err != nil {
return nil, err
}
if y == 0 {