starlark

package
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 Go to latest Published: Nov 25, 2024 License: BSD-3-Clause Imports: 29 Imported by: 806

Documentation

Overview

Package starlark provides a Starlark interpreter.

Starlark values are represented by the Value interface. The following built-in Value types are known to the evaluator: 

NoneType        -- NoneType
Bool            -- bool
Bytes           -- bytes
Int             -- int
Float           -- float
String          -- string
*List           -- list
Tuple           -- tuple
*Dict           -- dict
*Set            -- set
*Function       -- function (implemented in Starlark)
*Builtin        -- builtin_function_or_method (function or method implemented in Go)

Client applications may define new data types that satisfy at least the Value interface. Such types may provide additional operations by implementing any of these optional interfaces: 

Callable        -- value is callable like a function
Comparable      -- value defines its own comparison operations
Iterable        -- value is iterable using 'for' loops
Sequence        -- value is iterable sequence of known length
Indexable       -- value is sequence with efficient random access
Mapping         -- value maps from keys to values, like a dictionary
HasBinary       -- value defines binary operations such as * and +
HasAttrs        -- value has readable fields or methods x.f
HasSetField     -- value has settable fields x.f
HasSetIndex     -- value supports element update using x[i]=y
HasSetKey       -- value supports map update using x[k]=v
HasUnary        -- value defines unary operations such as + and -

Client applications may also define domain-specific functions in Go and make them available to Starlark programs. Use NewBuiltin to construct a built-in value that wraps a Go function. The implementation of the Go function may use UnpackArgs to make sense of the positional and keyword arguments provided by the caller.

Starlark's None value is not equal to Go's nil. Go's nil is not a legal Starlark value, but the compiler will not stop you from converting nil to Value. Be careful to avoid allowing Go nil values to leak into Starlark data structures.

The Compare operation requires two arguments of the same type, but this constraint cannot be expressed in Go's type system. (This is the classic "binary method problem".) So, each Value type's CompareSameType method is a partial function that compares a value only against others of the same type. Use the package's standalone Compare (or Equal) function to compare an arbitrary pair of values.

To parse and evaluate a Starlark source file, use ExecFile. The Eval function evaluates a single expression. All evaluator functions require a Thread parameter which defines the "thread-local storage" of a Starlark thread and may be used to plumb application state through Starlark code and into callbacks. When evaluation fails it returns an EvalError from which the application may obtain a backtrace of active Starlark calls.

Index

Examples

Constants

View Source 
const CompilerVersion = compile.Version

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.

View Source 
const None = NoneType(0)

Variables

View Source 
var CompareLimit = 10

CompareLimit is the depth limit on recursive comparison operations such as == and <. Comparison of data structures deeper than this limit may fail.

Functions

func AsFloat 

func AsFloat(x Value) (f float64, ok bool)

AsFloat returns the float64 value closest to x. The f result is undefined if x is not a float or Int. The result may be infinite if x is a very large Int.

func AsInt 

func AsInt(x Value, ptr interface{}) error

AsInt sets *ptr to the value of Starlark int x, if it is exactly representable, otherwise it returns an error. The type of ptr must be one of the pointer types *int, *int8, *int16, *int32, or *int64, or one of their unsigned counterparts including *uintptr.

func AsInt32 

func AsInt32(x Value) (int, error)

AsInt32 returns the value of x if is representable as an int32.

func AsString 

func AsString(x Value) (string, bool)

func Compare 

func Compare(op syntax.Token, x, y Value) (bool, error)

Compare compares two Starlark values. The comparison operation must be one of EQL, NEQ, LT, LE, GT, or GE. Compare returns an error if an ordered comparison was requested for a type that does not support it.

Recursive comparisons by implementations of Value.CompareSameType should use CompareDepth to prevent infinite recursion.

func CompareDepth 

func CompareDepth(op syntax.Token, x, y Value, depth int) (bool, error)

CompareDepth compares two Starlark values. The comparison operation must be one of EQL, NEQ, LT, LE, GT, or GE. CompareDepth returns an error if an ordered comparison was requested for a pair of values that do not support it.

The depth parameter limits the maximum depth of recursion in cyclic data structures.

func Elements 

func Elements(iterable Iterable) iter.Seq[Value]

Elements returns an iterator for the elements of the iterable value.

Example of go1.23 iteration: 

for elem := range Elements(iterable) { ... }

Push iterators are provided as a convenience for Go client code. The core iteration behavior of Starlark for-loops is defined by the Iterable interface.

func Entries 

func Entries(mapping IterableMapping) iter.Seq2[Value, Value]

Entries returns an iterator over the entries (key/value pairs) of the iterable mapping.

Example of go1.23 iteration: 

for k, v := range Entries(mapping) { ... }

Push iterators are provided as a convenience for Go client code. The core iteration behavior of Starlark for-loops is defined by the Iterable interface.

func Equal 

func Equal(x, y Value) (bool, error)

Equal reports whether two Starlark values are equal.

func EqualDepth 

func EqualDepth(x, y Value, depth int) (bool, error)

EqualDepth reports whether two Starlark values are equal.

Recursive comparisons by implementations of Value.CompareSameType should use EqualDepth to prevent infinite recursion.

func ExecREPLChunk 

func ExecREPLChunk(f *syntax.File, thread *Thread, globals StringDict) error

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 Len 

func Len(x Value) int

Len returns the length of a string or sequence value, and -1 for all others.

Warning: Len(x) >= 0 does not imply Iterate(x) != nil. A string has a known length but is not directly iterable.

func StartProfile 

func StartProfile(w io.Writer) error

StartProfile enables time profiling of all Starlark threads, and writes a profile in pprof format to w. It must be followed by a call to StopProfiler to stop the profiler and finalize the profile.

StartProfile returns an error if profiling was already enabled.

StartProfile must not be called concurrently with Starlark execution.

func StopProfile 

func StopProfile() error

StopProfile stops the profiler started by a prior call to StartProfile and finalizes the profile. It returns an error if the profile could not be completed.

StopProfile must not be called concurrently with Starlark execution.

func UnpackArgs 

func UnpackArgs(fnname string, args Tuple, kwargs []Tuple, pairs ...any) error

UnpackArgs unpacks the positional and keyword arguments into the supplied parameter variables. pairs is an alternating list of names and pointers to variables.

If the variable is a bool, integer, string, *List, *Dict, Callable, Iterable, or user-defined implementation of Value, UnpackArgs performs the appropriate type check. Predeclared Go integer types use the AsInt check.

If the parameter name ends with "?", it is optional.

If the parameter name ends with "??", it is optional and treats the None value as if the argument was absent.

If a parameter is marked optional, then all following parameters are implicitly optional whether or not they are marked.

If the variable implements Unpacker, its Unpack argument is called with the argument value, allowing an application to define its own argument validation and conversion.

If the variable implements Value, UnpackArgs may call its Type() method while constructing the error message.

Examples: 

var (
    a Value
    b = MakeInt(42)
    c Value = starlark.None
)

// 1. mixed parameters, like def f(a, b=42, c=None).
err := UnpackArgs("f", args, kwargs, "a", &a, "b?", &b, "c?", &c)

// 2. keyword parameters only, like def f(*, a, b, c=None).
if len(args) > 0 {
        return fmt.Errorf("f: unexpected positional arguments")
}
err := UnpackArgs("f", args, kwargs, "a", &a, "b?", &b, "c?", &c)

// 3. positional parameters only, like def f(a, b=42, c=None, /) in Python 3.8.
err := UnpackPositionalArgs("f", args, kwargs, 1, &a, &b, &c)

More complex forms such as def f(a, b=42, *args, c, d=123, **kwargs) require additional logic, but their need in built-ins is exceedingly rare.

In the examples above, the declaration of b with type Int causes UnpackArgs to require that b's argument value, if provided, is also an int. To allow arguments of any type, while retaining the default value of 42, declare b as a Value: 

var b Value = MakeInt(42)

The zero value of a variable of type Value, such as 'a' in the examples above, is not a valid Starlark value, so if the parameter is optional, the caller must explicitly handle the default case by interpreting nil as None or some computed default. The same is true for the zero values of variables of type *List, *Dict, Callable, or Iterable. For example: 

// def myfunc(d=None, e=[], f={})
var (
    d Value
    e *List
    f *Dict
)
err := UnpackArgs("myfunc", args, kwargs, "d?", &d, "e?", &e, "f?", &f)
if d == nil { d = None; }
if e == nil { e = new(List); }
if f == nil { f = new(Dict); }

func UnpackPositionalArgs 

func UnpackPositionalArgs(fnname string, args Tuple, kwargs []Tuple, min int, vars ...any) error

UnpackPositionalArgs unpacks the positional arguments into corresponding variables. Each element of vars is a pointer; see UnpackArgs for allowed types and conversions.

UnpackPositionalArgs reports an error if the number of arguments is less than min or greater than len(vars), if kwargs is nonempty, or if any conversion fails.

See UnpackArgs for general comments.

Types

type Binding 

type Binding struct {
	Name string
	Pos  syntax.Position
}

A Binding is the name and position of a binding identifier.

type Bool 

type Bool bool

Bool is the type of a Starlark bool. 

const (
	False Bool = false
	True  Bool = true
)

func (Bool) CompareSameType 

func (x Bool) CompareSameType(op syntax.Token, y_ Value, depth int) (bool, error)

func (Bool) Freeze 

func (b Bool) Freeze()

func (Bool) Hash 

func (b Bool) Hash() (uint32, error)

func (Bool) String 

func (b Bool) String() string

func (Bool) Truth 

func (b Bool) Truth() Bool

func (Bool) Type 

func (b Bool) Type() string

type Builtin 

type Builtin struct {
	// contains filtered or unexported fields
}

A Builtin is a function implemented in Go.

func NewBuiltin 

func NewBuiltin(name string, fn func(thread *Thread, fn *Builtin, args Tuple, kwargs []Tuple) (Value, error)) *Builtin

NewBuiltin returns a new 'builtin_function_or_method' value with the specified name and implementation. It compares unequal with all other values.

func (*Builtin) BindReceiver 

func (b *Builtin) BindReceiver(recv Value) *Builtin

BindReceiver returns a new Builtin value representing a method closure, that is, a built-in function bound to a receiver value.

In the example below, the value of f is the string.index built-in method bound to the receiver value "abc": 

f = "abc".index; f("a"); f("b")

In the common case, the receiver is bound only during the call, but this still results in the creation of a temporary method closure: 

"abc".index("a")

func (*Builtin) CallInternal 

func (b *Builtin) CallInternal(thread *Thread, args Tuple, kwargs []Tuple) (Value, error)

func (*Builtin) Freeze 

func (b *Builtin) Freeze()

func (*Builtin) Hash 

func (b *Builtin) Hash() (uint32, error)

func (*Builtin) Name 

func (b *Builtin) Name() string

func (*Builtin) Receiver 

func (b *Builtin) Receiver() Value

func (*Builtin) String 

func (b *Builtin) String() string

func (*Builtin) Truth 

func (b *Builtin) Truth() Bool

func (*Builtin) Type 

func (b *Builtin) Type() string

type Bytes 

type Bytes string

Bytes is the type of a Starlark binary string.

A Bytes encapsulates an immutable sequence of bytes. It is comparable, indexable, and sliceable, but not directly iterable; use bytes.elems() for an iterable view.

In this Go implementation, the elements of 'string' and 'bytes' are both bytes, but in other implementations, notably Java, the elements of a 'string' are UTF-16 codes (Java chars). The spec abstracts text strings as sequences of UTF-k codes that encode Unicode code points, and operations that convert from text to binary incur UTF-k-to-UTF-8 transcoding; conversely, conversion from binary to text incurs UTF-8-to-UTF-k transcoding. Because k=8 for Go, these operations are the identity function, at least for valid encodings of text.

func (Bytes) Attr 

func (b Bytes) Attr(name string) (Value, error)

func (Bytes) AttrNames 

func (b Bytes) AttrNames() []string

func (Bytes) CompareSameType 

func (x Bytes) CompareSameType(op syntax.Token, y_ Value, depth int) (bool, error)

func (Bytes) Freeze 

func (b Bytes) Freeze()

func (Bytes) Hash 

func (b Bytes) Hash() (uint32, error)

func (Bytes) Index 

func (b Bytes) Index(i int) Value

func (Bytes) Len 

func (b Bytes) Len() int

func (Bytes) Slice 

func (b Bytes) Slice(start, end, step int) Value

func (Bytes) String 

func (b Bytes) String() string

func (Bytes) Truth 

func (b Bytes) Truth() Bool

func (Bytes) Type 

func (b Bytes) Type() string

type CallFrame 

type CallFrame struct {
	Name string
	Pos  syntax.Position
}

A CallFrame represents the function name and current position of execution of an enclosing call frame.

type CallStack 

type CallStack []CallFrame

A CallStack is a stack of call frames, outermost first.

func (CallStack) At 

func (stack CallStack) At(i int) CallFrame

At returns a copy of the frame at depth i. At(0) returns the topmost frame.

func (*CallStack) Pop 

func (stack *CallStack) Pop() CallFrame

Pop removes and returns the topmost frame.

func (CallStack) String 

func (stack CallStack) String() string

String returns a user-friendly description of the stack.

type Callable 

type Callable interface {
	Value
	Name() string
	CallInternal(thread *Thread, args Tuple, kwargs []Tuple) (Value, error)
}

A Callable value f may be the operand of a function call, f(x).

Clients should use the Call function, never the CallInternal method.

type Comparable 

type Comparable interface {
	Value
	// CompareSameType compares one value to another of the same Type().
	// The comparison operation must be one of EQL, NEQ, LT, LE, GT, or GE.
	// CompareSameType returns an error if an ordered comparison was
	// requested for a type that does not support it.
	//
	// Implementations that recursively compare subcomponents of
	// the value should use the CompareDepth function, not Compare, to
	// avoid infinite recursion on cyclic structures.
	//
	// The depth parameter is used to bound comparisons of cyclic
	// data structures.  Implementations should decrement depth
	// before calling CompareDepth and should return an error if depth
	// < 1.
	//
	// Client code should not call this method.  Instead, use the
	// standalone Compare or Equals functions, which are defined for
	// all pairs of operands.
	CompareSameType(op syntax.Token, y Value, depth int) (bool, error)
}

A Comparable is a value that defines its own equivalence relation and perhaps ordered comparisons.

type DebugFrame 

type DebugFrame interface {
	Callable() Callable           // returns the frame's function
	NumLocals() int               // returns the number of local variables in this frame
	Local(i int) (Binding, Value) // returns the binding and value of the (Starlark) frame's ith local variable
	Position() syntax.Position    // returns the current position of execution in this frame
}

DebugFrame is the debugger API for a frame of the interpreter's call stack.

Most applications have no need for this API; use CallFrame instead.

It may be tempting to use this interface when implementing built-in functions. Beware that reflection over the call stack is easily abused, leading to built-in functions whose behavior is mysterious and unpredictable.

Clients must not retain a DebugFrame nor call any of its methods once the current built-in call has returned or execution has resumed after a breakpoint as this may have unpredictable effects, including but not limited to retention of object that would otherwise be garbage.

type Dict 

type Dict struct {
	// contains filtered or unexported fields
}

A *Dict represents a Starlark dictionary. The zero value of Dict is a valid empty dictionary. If you know the exact final number of entries, it is more efficient to call NewDict.

func NewDict 

func NewDict(size int) *Dict

NewDict returns a set with initial space for at least size insertions before rehashing.

func (*Dict) Attr 

func (d *Dict) Attr(name string) (Value, error)

func (*Dict) AttrNames 

func (d *Dict) AttrNames() []string

func (*Dict) Clear 

func (d *Dict) Clear() error

func (*Dict) CompareSameType 

func (x *Dict) CompareSameType(op syntax.Token, y_ Value, depth int) (bool, error)

func (*Dict) Delete 

func (d *Dict) Delete(k Value) (v Value, found bool, err error)

func (*Dict) Entries 

func (d *Dict) Entries() iter.Seq2[Value, Value]

func (*Dict) Freeze 

func (d *Dict) Freeze()

func (*Dict) Get 

func (d *Dict) Get(k Value) (v Value, found bool, err error)

func (*Dict) Hash 

func (d *Dict) Hash() (uint32, error)

func (*Dict) Items 

func (d *Dict) Items() []Tuple

func (*Dict) Iterate 

func (d *Dict) Iterate() Iterator

func (*Dict) Keys 

func (d *Dict) Keys() []Value

func (*Dict) Len 

func (d *Dict) Len() int

func (*Dict) SetKey 

func (d *Dict) SetKey(k, v Value) error

func (*Dict) String 

func (d *Dict) String() string

func (*Dict) Truth 

func (d *Dict) Truth() Bool

func (*Dict) Type 

func (d *Dict) Type() string

func (*Dict) Union 

func (x *Dict) Union(y *Dict) *Dict

type EvalError 

type EvalError struct {
	Msg       string
	CallStack CallStack
	// contains filtered or unexported fields
}

An EvalError is a Starlark evaluation error and a copy of the thread's stack at the moment of the error.

func (*EvalError) Backtrace 

func (e *EvalError) Backtrace() string

Backtrace returns a user-friendly error message describing the stack of calls that led to this error.

func (*EvalError) Error 

func (e *EvalError) Error() string

func (*EvalError) Unwrap 

func (e *EvalError) Unwrap() error

type Float 

type Float float64

Float is the type of a Starlark float.

func (Float) Cmp 

func (f Float) Cmp(v Value, depth int) (int, error)

Cmp implements comparison of two Float values. Required by the TotallyOrdered interface.

func (Float) Freeze 

func (f Float) Freeze()

func (Float) Hash 

func (f Float) Hash() (uint32, error)

func (Float) Mod 

func (x Float) Mod(y Float) Float

func (Float) String 

func (f Float) String() string

func (Float) Truth 

func (f Float) Truth() Bool

func (Float) Type 

func (f Float) Type() string

func (Float) Unary 

func (f Float) Unary(op syntax.Token) (Value, error)

Unary implements the operations +float and -float.

type Function 

type Function struct {
	// contains filtered or unexported fields
}

A Function is a function defined by a Starlark def statement or lambda expression. The initialization behavior of a Starlark module is also represented by a Function.

func ExprFunc deprecated 

func ExprFunc(filename string, src interface{}, env StringDict) (*Function, error)

ExprFunc calls ExprFuncOptions using syntax.LegacyFileOptions.

Deprecated: use ExprFuncOptions with syntax.FileOptions instead, because this function relies on legacy global variables.

func ExprFuncOptions 

func ExprFuncOptions(options *syntax.FileOptions, filename string, src interface{}, env StringDict) (*Function, error)

ExprFunc returns a no-argument function that evaluates the expression whose source is src.

func (*Function) CallInternal 

func (fn *Function) CallInternal(thread *Thread, args Tuple, kwargs []Tuple) (Value, error)

func (*Function) Doc 

func (fn *Function) Doc() string

func (*Function) FreeVar 

func (fn *Function) FreeVar(i int) (Binding, Value)

FreeVar returns the binding (name and binding position) and value of the i'th free variable of function fn.

func (*Function) Freeze 

func (fn *Function) Freeze()

func (*Function) Globals 

func (fn *Function) Globals() StringDict

Globals returns a new, unfrozen StringDict containing all global variables so far defined in the function's module.

func (*Function) HasKwargs 

func (fn *Function) HasKwargs() bool

func (*Function) HasVarargs 

func (fn *Function) HasVarargs() bool

func (*Function) Hash 

func (fn *Function) Hash() (uint32, error)

func (*Function) Name 

func (fn *Function) Name() string

func (*Function) NumFreeVars 

func (fn *Function) NumFreeVars() int

NumFreeVars returns the number of free variables of this function.

func (*Function) NumKwonlyParams 

func (fn *Function) NumKwonlyParams() int

func (*Function) NumParams 

func (fn *Function) NumParams() int

func (*Function) Param 

func (fn *Function) Param(i int) (string, syntax.Position)

Param returns the name and position of the ith parameter, where 0 <= i < NumParams(). The *args and **kwargs parameters are at the end even if there were optional parameters after *args.

func (*Function) ParamDefault 

func (fn *Function) ParamDefault(i int) Value

ParamDefault returns the default value of the specified parameter (0 <= i < NumParams()), or nil if the parameter is not optional.

func (*Function) Position 

func (fn *Function) Position() syntax.Position

func (*Function) String 

func (fn *Function) String() string

func (*Function) Truth 

func (fn *Function) Truth() Bool

func (*Function) Type 

func (fn *Function) Type() string

type HasAttrs 

type HasAttrs interface {
	Value
	Attr(name string) (Value, error) // returns (nil, nil) if attribute not present
	AttrNames() []string             // callers must not modify the result.
}

A HasAttrs value has fields or methods that may be read by a dot expression (y = x.f). Attribute names may be listed using the built-in 'dir' function.

For implementation convenience, a result of (nil, nil) from Attr is interpreted as a "no such field or method" error. Implementations are free to return a more precise error.

type HasBinary 

type HasBinary interface {
	Value
	Binary(op syntax.Token, y Value, side Side) (Value, error)
}

A HasBinary value may be used as either operand of these binary operators: + - * / // % in not in | & ^ << >>

The Side argument indicates whether the receiver is the left or right operand.

An implementation may decline to handle an operation by returning (nil, nil). For this reason, clients should always call the standalone Binary(op, x, y) function rather than calling the method directly.

type HasSetField 

type HasSetField interface {
	HasAttrs
	SetField(name string, val Value) error
}

A HasSetField value has fields that may be written by a dot expression (x.f = y).

An implementation of SetField may return a NoSuchAttrError, in which case the runtime may augment the error message to warn of possible misspelling.

type HasSetIndex 

type HasSetIndex interface {
	Indexable
	SetIndex(index int, v Value) error
}

A HasSetIndex is an Indexable value whose elements may be assigned (x[i] = y).

The implementation should not add Len to a negative index as the evaluator does this before the call.

type HasSetKey 

type HasSetKey interface {
	Mapping
	SetKey(k, v Value) error
}

A HasSetKey supports map update using x[k]=v syntax, like a dictionary.

type HasUnary 

type HasUnary interface {
	Value
	Unary(op syntax.Token) (Value, error)
}

A HasUnary value may be used as the operand of these unary operators: + - ~

An implementation may decline to handle an operation by returning (nil, nil). For this reason, clients should always call the standalone Unary(op, x) function rather than calling the method directly.

type Indexable 

type Indexable interface {
	Value
	Index(i int) Value // requires 0 <= i < Len()
	Len() int
}

An Indexable is a sequence of known length that supports efficient random access. It is not necessarily iterable.

type Int 

type Int struct {
	// contains filtered or unexported fields
}

Int is the type of a Starlark int.

The zero value is not a legal value; use MakeInt(0).

func MakeBigInt 

func MakeBigInt(x *big.Int) Int

MakeBigInt returns a Starlark int for the specified big.Int. The new Int value will contain a copy of x. The caller is safe to modify x.

func MakeInt 

func MakeInt(x int) Int

MakeInt returns a Starlark int for the specified signed integer.

func MakeInt64 

func MakeInt64(x int64) Int

MakeInt64 returns a Starlark int for the specified int64.

func MakeUint 

func MakeUint(x uint) Int

MakeUint returns a Starlark int for the specified unsigned integer.

func MakeUint64 

func MakeUint64(x uint64) Int

MakeUint64 returns a Starlark int for the specified uint64.

func NumberToInt 

func NumberToInt(x Value) (Int, error)

NumberToInt converts a number x to an integer value. An int is returned unchanged, a float is truncated towards zero. NumberToInt reports an error for all other values.

func (Int) Add 

func (x Int) Add(y Int) Int

func (Int) And 

func (x Int) And(y Int) Int

func (Int) BigInt 

func (i Int) BigInt() *big.Int

BigInt returns a new big.Int with the same value as the Int.

func (Int) Cmp 

func (i Int) Cmp(v Value, depth int) (int, error)

Cmp implements comparison of two Int values. Required by the TotallyOrdered interface.

func (Int) Div 

func (x Int) Div(y Int) Int

Precondition: y is nonzero.

func (Int) Float 

func (i Int) Float() Float

Float returns the float value nearest i.

func (Int) Format 

func (i Int) Format(s fmt.State, ch rune)

func (Int) Freeze 

func (i Int) Freeze()

func (Int) Hash 

func (i Int) Hash() (uint32, error)

func (Int) Int64 

func (i Int) Int64() (_ int64, ok bool)

Int64 returns the value as an int64. If it is not exactly representable the result is undefined and ok is false.

func (Int) Lsh 

func (x Int) Lsh(y uint) Int

func (Int) Mod 

func (x Int) Mod(y Int) Int

Precondition: y is nonzero.

func (Int) Mul 

func (x Int) Mul(y Int) Int

func (Int) Not 

func (x Int) Not() Int

func (Int) Or 

func (x Int) Or(y Int) Int

func (Int) Rsh 

func (x Int) Rsh(y uint) Int

func (Int) Sign 

func (x Int) Sign() int

func (Int) String 

func (i Int) String() string

func (Int) Sub 

func (x Int) Sub(y Int) Int

func (Int) Truth 

func (i Int) Truth() Bool

func (Int) Type 

func (i Int) Type() string

func (Int) Uint64 

func (i Int) Uint64() (_ uint64, ok bool)

Uint64 returns the value as a uint64. If it is not exactly representable the result is undefined and ok is false.

func (Int) Unary 

func (i Int) Unary(op syntax.Token) (Value, error)

Unary implements the operations +int, -int, and ~int.

func (Int) Xor 

func (x Int) Xor(y Int) Int

type Iterable 

type Iterable interface {
	Value
	Iterate() Iterator // must be followed by call to Iterator.Done
}

An Iterable abstracts a sequence of values. An iterable value may be iterated over by a 'for' loop or used where any other Starlark iterable is allowed. Unlike a Sequence, the length of an Iterable is not necessarily known in advance of iteration.

type IterableMapping 

type IterableMapping interface {
	Mapping
	Iterate() Iterator // see Iterable interface
	Items() []Tuple    // a new slice containing all key/value pairs
}

An IterableMapping is a mapping that supports key enumeration.

See Entries for example use.

type Iterator 

type Iterator interface {
	// If the iterator is exhausted, Next returns false.
	// Otherwise it sets *p to the current element of the sequence,
	// advances the iterator, and returns true.
	Next(p *Value) bool
	Done()
}

An Iterator provides a sequence of values to the caller.

The caller must call Done when the iterator is no longer needed. Operations that modify a sequence will fail if it has active iterators.

Example usage: 

var seq Iterator = ...
iter := seq.Iterate()
defer iter.Done()
var elem Value
for iter.Next(elem) {
	...
}

Or, using go1.23 iterators: 

for elem := range Elements(seq) { ... }

func Iterate 

func Iterate(x Value) Iterator

Iterate return a new iterator for the value if iterable, nil otherwise. If the result is non-nil, the caller must call Done when finished with it.

Warning: Iterate(x) != nil does not imply Len(x) >= 0. Some iterables may have unknown length.

type List 

type List struct {
	// contains filtered or unexported fields
}

A *List represents a Starlark list value.

func NewList 

func NewList(elems []Value) *List

NewList returns a list containing the specified elements. Callers should not subsequently modify elems.

func (*List) Append 

func (l *List) Append(v Value) error

func (*List) Attr 

func (l *List) Attr(name string) (Value, error)

func (*List) AttrNames 

func (l *List) AttrNames() []string

func (*List) Clear 

func (l *List) Clear() error

func (*List) CompareSameType 

func (x *List) CompareSameType(op syntax.Token, y_ Value, depth int) (bool, error)

func (*List) Elements 

func (l *List) Elements() iter.Seq[Value]

Elements returns a go1.23 iterator over the elements of the list.

Example: 

for elem := range list.Elements() { ... }

func (*List) Freeze 

func (l *List) Freeze()

func (*List) Hash 

func (l *List) Hash() (uint32, error)

func (*List) Index 

func (l *List) Index(i int) Value

func (*List) Iterate 

func (l *List) Iterate() Iterator

func (*List) Len 

func (l *List) Len() int

func (*List) SetIndex 

func (l *List) SetIndex(i int, v Value) error

func (*List) Slice 

func (l *List) Slice(start, end, step int) Value

func (*List) String 

func (l *List) String() string

func (*List) Truth 

func (l *List) Truth() Bool

func (*List) Type 

func (l *List) Type() string

type Mapping 

type Mapping interface {
	Value
	// Get returns the value corresponding to the specified key,
	// or !found if the mapping does not contain the key.
	//
	// Get also defines the behavior of "v in mapping".
	// The 'in' operator reports the 'found' component, ignoring errors.
	Get(Value) (v Value, found bool, err error)
}

A Mapping is a mapping from keys to values, such as a dictionary.

If a type satisfies both Mapping and Iterable, the iterator yields the keys of the mapping.

type NoSuchAttrError 

type NoSuchAttrError string

A NoSuchAttrError may be returned by an implementation of HasAttrs.Attr or HasSetField.SetField to indicate that no such field exists. In that case the runtime may augment the error message to warn of possible misspelling.

func (NoSuchAttrError) Error 

func (e NoSuchAttrError) Error() string

type NoneType 

type NoneType byte

NoneType is the type of None. Its only legal value is None. (We represent it as a number, not struct{}, so that None may be constant.)

func (NoneType) Freeze 

func (NoneType) Freeze()

func (NoneType) Hash 

func (NoneType) Hash() (uint32, error)

func (NoneType) String 

func (NoneType) String() string

func (NoneType) Truth 

func (NoneType) Truth() Bool

func (NoneType) Type 

func (NoneType) Type() string

type Program 

type Program struct {
	// contains filtered or unexported fields
}

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).

func CompiledProgram 

func CompiledProgram(in io.Reader) (*Program, error)

CompiledProgram produces a new program from the representation of a compiled program previously saved by Program.Write.

func FileProgram 

func FileProgram(f *syntax.File, isPredeclared func(string) bool) (*Program, error)

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 SourceProgram deprecated 

func SourceProgram(filename string, src interface{}, isPredeclared func(string) bool) (*syntax.File, *Program, error)

SourceProgram calls SourceProgramOptions using syntax.LegacyFileOptions.

Deprecated: use SourceProgramOptions with syntax.FileOptions instead, because this function relies on legacy global variables.

func SourceProgramOptions 

func SourceProgramOptions(opts *syntax.FileOptions, filename string, src interface{}, isPredeclared func(string) bool) (*syntax.File, *Program, error)

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 (*Program) Filename 

func (prog *Program) Filename() string

Filename returns the name of the file from which this program was loaded.

func (*Program) Init 

func (prog *Program) Init(thread *Thread, predeclared StringDict) (StringDict, error)

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 (*Program) Load 

func (prog *Program) Load(i int) (string, syntax.Position)

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 (*Program) NumLoads 

func (prog *Program) NumLoads() int

NumLoads returns the number of load statements in the compiled program.

func (*Program) String 

func (prog *Program) String() string

func (*Program) Write 

func (prog *Program) Write(out io.Writer) error

WriteTo writes the compiled module to the specified output stream.

type Sequence 

type Sequence interface {
	Iterable
	Len() int
}

A Sequence is a sequence of values of known length.

type Set 

type Set struct {
	// contains filtered or unexported fields
}

A Set represents a Starlark set value. The zero value of Set is a valid empty set. If you know the exact final number of elements, it is more efficient to call NewSet.

func NewSet 

func NewSet(size int) *Set

NewSet returns a dictionary with initial space for at least size insertions before rehashing.

func (*Set) Attr 

func (s *Set) Attr(name string) (Value, error)

func (*Set) AttrNames 

func (s *Set) AttrNames() []string

func (*Set) Clear 

func (s *Set) Clear() error

func (*Set) CompareSameType 

func (x *Set) CompareSameType(op syntax.Token, y_ Value, depth int) (bool, error)

func (*Set) Delete 

func (s *Set) Delete(k Value) (found bool, err error)

func (*Set) Difference 

func (s *Set) Difference(other Iterator) (Value, error)

func (*Set) Elements 

func (s *Set) Elements() iter.Seq[Value]

func (*Set) Freeze 

func (s *Set) Freeze()

func (*Set) Has 

func (s *Set) Has(k Value) (found bool, err error)

func (*Set) Hash 

func (s *Set) Hash() (uint32, error)

func (*Set) Insert 

func (s *Set) Insert(k Value) error

func (*Set) Intersection 

func (s *Set) Intersection(other Iterator) (Value, error)

func (*Set) IsSubset 

func (s *Set) IsSubset(other Iterator) (bool, error)

func (*Set) IsSuperset 

func (s *Set) IsSuperset(other Iterator) (bool, error)

func (*Set) Iterate 

func (s *Set) Iterate() Iterator

func (*Set) Len 

func (s *Set) Len() int

func (*Set) String 

func (s *Set) String() string

func (*Set) SymmetricDifference 

func (s *Set) SymmetricDifference(other Iterator) (Value, error)

func (*Set) Truth 

func (s *Set) Truth() Bool

func (*Set) Type 

func (s *Set) Type() string

func (*Set) Union 

func (s *Set) Union(iter Iterator) (Value, error)

type Side 

type Side bool
const (
	Left  Side = false
	Right Side = true
)

type Sliceable 

type Sliceable interface {
	Indexable
	// For positive strides (step > 0), 0 <= start <= end <= n.
	// For negative strides (step < 0), -1 <= end <= start < n.
	// The caller must ensure that the start and end indices are valid
	// and that step is non-zero.
	Slice(start, end, step int) Value
}

A Sliceable is a sequence that can be cut into pieces with the slice operator (x[i:j:step]).

All native indexable objects are sliceable. This is a separate interface for backwards-compatibility.

type String 

type String string

String is the type of a Starlark text string.

A String encapsulates an immutable sequence of bytes, but strings are not directly iterable. Instead, iterate over the result of calling one of these four methods: codepoints, codepoint_ords, elems, elem_ords.

Strings typically contain text; use Bytes for binary strings. The Starlark spec defines text strings as sequences of UTF-k codes that encode Unicode code points. In this Go implementation, k=8, whereas in a Java implementation, k=16. For portability, operations on strings should aim to avoid assumptions about the value of k.

Warning: the contract of the Value interface's String method is that it returns the value printed in Starlark notation, so s.String() or fmt.Sprintf("%s", s) returns a quoted string. Use string(s) or s.GoString() or fmt.Sprintf("%#v", s) to obtain the raw contents of a Starlark string as a Go string.

func (String) Attr 

func (s String) Attr(name string) (Value, error)

func (String) AttrNames 

func (s String) AttrNames() []string

func (String) CompareSameType 

func (x String) CompareSameType(op syntax.Token, y_ Value, depth int) (bool, error)

func (String) Freeze 

func (s String) Freeze()

func (String) GoString 

func (s String) GoString() string

func (String) Hash 

func (s String) Hash() (uint32, error)

func (String) Index 

func (s String) Index(i int) Value

func (String) Len 

func (s String) Len() int

func (String) Slice 

func (s String) Slice(start, end, step int) Value

func (String) String 

func (s String) String() string

func (String) Truth 

func (s String) Truth() Bool

func (String) Type 

func (s String) Type() string

type StringDict 

type StringDict map[string]Value

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. 

var Universe StringDict

Universe defines the set of universal built-ins, such as None, True, and len.

The Go application may add or remove items from the universe dictionary before Starlark evaluation begins. All values in the dictionary must be immutable. Starlark programs cannot modify the dictionary.

func ExecFile deprecated 

func ExecFile(thread *Thread, filename string, src interface{}, predeclared StringDict) (StringDict, error)

ExecFile calls ExecFileOptions using syntax.LegacyFileOptions.

Deprecated: use ExecFileOptions with syntax.FileOptions instead, because this function relies on legacy global variables.

Example

ExampleExecFile demonstrates a simple embedding of the Starlark interpreter into a Go program. 

package main

import (
	"fmt"
	"log"
	"strings"

	"go.starlark.net/starlark"
)

func main() {
	const data = `
print(greeting + ", world")
print(repeat("one"))
print(repeat("mur", 2))
squares = [x*x for x in range(10)]
`

	// repeat(str, n=1) is a Go function called from Starlark.
	// It behaves like the 'string * int' operation.
	repeat := func(thread *starlark.Thread, b *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
		var s string
		var n int = 1
		if err := starlark.UnpackArgs(b.Name(), args, kwargs, "s", &s, "n?", &n); err != nil {
			return nil, err
		}
		return starlark.String(strings.Repeat(s, n)), nil
	}

	// The Thread defines the behavior of the built-in 'print' function.
	thread := &starlark.Thread{
		Name:  "example",
		Print: func(_ *starlark.Thread, msg string) { fmt.Println(msg) },
	}

	// This dictionary defines the pre-declared environment.
	predeclared := starlark.StringDict{
		"greeting": starlark.String("hello"),
		"repeat":   starlark.NewBuiltin("repeat", repeat),
	}

	// Execute a program.
	globals, err := starlark.ExecFile(thread, "apparent/filename.star", data, predeclared)
	if err != nil {
		if evalErr, ok := err.(*starlark.EvalError); ok {
			log.Fatal(evalErr.Backtrace())
		}
		log.Fatal(err)
	}

	// Print the global environment.
	fmt.Println("\nGlobals:")
	for _, name := range globals.Keys() {
		v := globals[name]
		fmt.Printf("%s (%s) = %s\n", name, v.Type(), v.String())
	}

}

Output:

hello, world
one
murmur

Globals:
squares (list) = [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

func ExecFileOptions 

func ExecFileOptions(opts *syntax.FileOptions, thread *Thread, filename string, src interface{}, predeclared StringDict) (StringDict, error)

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 (StringDict) Freeze 

func (d StringDict) Freeze()

func (StringDict) Has 

func (d StringDict) Has(key string) bool

Has reports whether the dictionary contains the specified key.

func (StringDict) Keys 

func (d StringDict) Keys() []string

Keys returns a new sorted slice of d's keys.

func (StringDict) String 

func (d StringDict) String() string

type Thread 

type Thread struct {
	// Name is an optional name that describes the thread, for debugging.
	Name string

	// 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 uint64
	// contains filtered or unexported fields
}

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.

func (*Thread) CallFrame 

func (thread *Thread) CallFrame(depth int) CallFrame

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) CallStack 

func (thread *Thread) CallStack() CallStack

CallStack returns a new slice containing the thread's stack of call frames.

func (*Thread) CallStackDepth 

func (thread *Thread) CallStackDepth() int

CallStackDepth returns the number of frames in the current call stack.

func (*Thread) Cancel 

func (thread *Thread) Cancel(reason string)

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) DebugFrame 

func (thread *Thread) DebugFrame(depth int) DebugFrame

DebugFrame returns the debugger interface for the specified frame of the interpreter's call stack. Frame numbering is as for Thread.CallFrame: 0 <= depth < thread.CallStackDepth().

This function is intended for use in debugging tools. Most applications should have no need for it; use CallFrame instead.

func (*Thread) ExecutionSteps 

func (thread *Thread) ExecutionSteps() uint64

ExecutionSteps returns the current value of Steps.

func (*Thread) Local 

func (thread *Thread) Local(key string) interface{}

Local returns the thread-local value associated with the specified key.

func (*Thread) SetLocal 

func (thread *Thread) SetLocal(key string, value interface{})

SetLocal sets the thread-local value associated with the specified key. It must not be called after execution begins.

func (*Thread) SetMaxExecutionSteps 

func (thread *Thread) SetMaxExecutionSteps(max uint64)

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) Uncancel 

func (thread *Thread) Uncancel()

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.

type TotallyOrdered 

type TotallyOrdered interface {
	Value
	// Cmp compares two values x and y of the same totally ordered type.
	// It returns negative if x < y, positive if x > y, and zero if the values are equal.
	//
	// Implementations that recursively compare subcomponents of
	// the value should use the CompareDepth function, not Cmp, to
	// avoid infinite recursion on cyclic structures.
	//
	// The depth parameter is used to bound comparisons of cyclic
	// data structures.  Implementations should decrement depth
	// before calling CompareDepth and should return an error if depth
	// < 1.
	//
	// Client code should not call this method.  Instead, use the
	// standalone Compare or Equals functions, which are defined for
	// all pairs of operands.
	Cmp(y Value, depth int) (int, error)
}

A TotallyOrdered is a type whose values form a total order: if x and y are of the same TotallyOrdered type, then x must be less than y, greater than y, or equal to y.

It is simpler than Comparable and should be preferred in new code, but if a type implements both interfaces, Comparable takes precedence.

type Tuple 

type Tuple []Value

A Tuple represents a Starlark tuple value.

func (Tuple) CompareSameType 

func (x Tuple) CompareSameType(op syntax.Token, y_ Value, depth int) (bool, error)

func (Tuple) Elements 

func (t Tuple) Elements() iter.Seq[Value]

Elements returns a go1.23 iterator over the elements of the tuple.

(A Tuple is a slice, so it is of course directly iterable. This method exists to provide a fast path for the Elements standalone function.)

func (Tuple) Freeze 

func (t Tuple) Freeze()

func (Tuple) Hash 

func (t Tuple) Hash() (uint32, error)

func (Tuple) Index 

func (t Tuple) Index(i int) Value

func (Tuple) Iterate 

func (t Tuple) Iterate() Iterator

func (Tuple) Len 

func (t Tuple) Len() int

func (Tuple) Slice 

func (t Tuple) Slice(start, end, step int) Value

func (Tuple) String 

func (t Tuple) String() string

func (Tuple) Truth 

func (t Tuple) Truth() Bool

func (Tuple) Type 

func (t Tuple) Type() string

type Unpacker 

type Unpacker interface {
	Unpack(v Value) error
}

An Unpacker defines custom argument unpacking behavior. See UnpackArgs.

type Value 

type Value interface {
	// String returns the string representation of the value.
	// Starlark string values are quoted as if by Python's repr.
	String() string

	// Type returns a short string describing the value's type.
	Type() string

	// Freeze causes the value, and all values transitively
	// reachable from it through collections and closures, to be
	// marked as frozen.  All subsequent mutations to the data
	// structure through this API will fail dynamically, making the
	// data structure immutable and safe for publishing to other
	// Starlark interpreters running concurrently.
	//
	// Implementations of Freeze must be defensive against
	// reference cycles; this can be achieved by first checking
	// the value's frozen state, then setting it, and only then
	// visiting any other values that it references.
	Freeze()

	// Truth returns the truth value of an object.
	Truth() Bool

	// Hash returns a function of x such that Equals(x, y) => Hash(x) == Hash(y).
	// Hash may fail if the value's type is not hashable, or if the value
	// contains a non-hashable value. The hash is used only by dictionaries and
	// is not exposed to the Starlark program.
	Hash() (uint32, error)
}

Value is a value in the Starlark interpreter.

func Binary 

func Binary(op syntax.Token, x, y Value) (Value, error)

Binary applies a strict binary operator (not AND or OR) to its operands. For equality tests or ordered comparisons, use Compare instead.

func Call 

func Call(thread *Thread, fn Value, args Tuple, kwargs []Tuple) (Value, error)

Call calls the function fn with the specified positional and keyword arguments.

func Eval deprecated 

func Eval(thread *Thread, filename string, src interface{}, env StringDict) (Value, error)

Eval calls EvalOptions using syntax.LegacyFileOptions.

Deprecated: use EvalOptions with syntax.FileOptions instead, because this function relies on legacy global variables.

func EvalExpr deprecated 

func EvalExpr(thread *Thread, expr syntax.Expr, env StringDict) (Value, error)

EvalExpr calls EvalExprOptions using syntax.LegacyFileOptions.

Deprecated: use EvalExprOptions with syntax.FileOptions instead, because this function relies on legacy global variables.

func EvalExprOptions 

func EvalExprOptions(opts *syntax.FileOptions, thread *Thread, expr syntax.Expr, env StringDict) (Value, error)

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 EvalOptions 

func EvalOptions(opts *syntax.FileOptions, thread *Thread, filename string, src interface{}, env StringDict) (Value, error)

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 Unary 

func Unary(op syntax.Token, x Value) (Value, error)

Unary applies a unary operator (+, -, ~, not) to its operand.

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