sx

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 Go to latest Published: Apr 3, 2024 License: EUPL-1.2 Imports: 7 Imported by: 5

README

sx - symbolic expressions

Sx is a collection of libraries and frameworks to work with s-expressions.

See for more information on its project page.

Types

Sx support the following atomic, immutable types:

  • Numbers contain numeric values. Currently, only integer values are supported. There is no maximum or minimum integer value. They optionally start with a + or - sign and contain only digits 0, ..., 9.
  • Strings are UTF-8 encoded Unicode character sequences. They are delimited by " characters. Special characters inside the string, like the " character itself, are escaped by the \ character.
  • Symbols are sequences of printable / visible Unicode characters. They are typically used to bind them to values within an environment. Another use case is symbolic computation.

Sx supports nested lists. A list is delimited by parentheses: ( ... ). Within a list, all values are separated by space characters, including new line. Lists can be nested. Internally, lists are created by pairs. The first part of a pair, called "car", contains the actual value stored at the beginning of a list. The second part, called "cdr", typically links to the next pair. This allows multiple lists to share elements. A proper list is a list, where the last elements second part is the empty list. The last element of a list may be a pair, where the second part references a values except a list. Such lists are improper lists. Since the second part may reference any value, even earlier elements of a list, lists may be circular. Single pairs are denoted as (X . Y), where the car references S and the cdr references Y (Y is not a list).

All other types supported by Sx cannot be specified via the reader.

  • Vector is a mutable sequence of values, to be used if direct access to values of a longer sequence is needed. A list has only O(n) access. Vectors are typically more memory efficient, compared to pair lists. However, they cannot be process recursively and they are not able to share elements.
  • Undefined contains just the undefined value. It is signalled by some functions that should not abort with an error.

There is no special boolean value. The empty list (), the empty string "", and the undefined value are considered as a "false" value. All other values are treated as a "true" value. Most functions that return a boolean value currently return the empty list to signal a "false" value or return either the number 1 or the symbol T as a "true" value.

Vectors and lists are both sequences and share some common functions / methods. You can calculate the length of a sequence, check for a length less than a value, fetch the n-th element of a sequence, convert a sequence to a pair list, and iterate over the elements in a ordered way.

Documentation

Overview

Package sx provides the basic objects to work with symbolic expressions.

Index

Constants

View Source 
const VectorName = "vector"

VectorName is the name of the (vector ...) builtin

Variables

View Source 
var (
	SymbolQuote           = MakeSymbol("quote")
	SymbolQuasiquote      = MakeSymbol("quasiquote")
	SymbolUnquote         = MakeSymbol("unquote")
	SymbolUnquoteSplicing = MakeSymbol("unquote-splicing")
)

Names of quotation symbols.

Used in packages sxbuiltins, sxreader.

View Source 
var ErrZeroNotAllowed = errors.New("number zero not allowed")

ErrZeroNotAllowed is signalled with an argument must not be zero, e.g. for division.

View Source 
var SymbolList = MakeSymbol("list")

SymbolList is the symbol of the (list ...) function.

View Source 
var T = MakeSymbol("T")

T is the default true object.

Functions

func IsFalse 

func IsFalse(obj Object) bool

IsFalse returns true, if the object is a false value.

func IsList 

func IsList(obj Object) bool

IsList returns true, if the object is a list, not just a pair. A list must have a nil value at the last cdr.

func IsNil 

func IsNil(obj Object) bool

IsNil returns true, if the given object is the nil object.

func IsTrue 

func IsTrue(obj Object) bool

IsTrue returns true, if object is a true value.

Everything except a nil object and the empty string, is a true value.

func IsUndefined 

func IsUndefined(obj Object) bool

IsUndefined returns true iff the object is a undefined value

func NumCmp 

func NumCmp(x, y Number) int

NumCmp compares the two number and returns -1 if x < y, 0 if x = y, and 1 if x > y.

func Print 

func Print(w io.Writer, obj Object) (int, error)

Print writes the string representation to a io.Writer.

Types

type ErrImproper 

type ErrImproper struct{ Pair *Pair }

ErrImproper is signalled if an improper list is found where it is not appropriate.

func (ErrImproper) Error 

func (err ErrImproper) Error() string

Error returns a textual representation for this error.

type Int64 

type Int64 int64

Int64 is a number that store 64 bit integer values.

func (Int64) GoString 

func (i Int64) GoString() string

GoString returns the Go string representation.

func (Int64) IsAtom 

func (Int64) IsAtom() bool

func (Int64) IsEqual 

func (i Int64) IsEqual(other Object) bool

IsEqual compare two objects.

func (Int64) IsNil 

func (i Int64) IsNil() bool

IsNil return true, if it is a nil integer value.

func (Int64) IsZero 

func (i Int64) IsZero() bool

func (Int64) String 

func (i Int64) String() string

String returns the string representation.

type ListBuilder 

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

ListBuilder is a helper to build a list sequentially from start to end.

func (*ListBuilder) Add 

func (lb *ListBuilder) Add(obj Object)

Add an object to the list.

func (*ListBuilder) ExtendBang 

func (lb *ListBuilder) ExtendBang(lst *Pair)

ExtendBang the list by the given list, reusing the given list

func (*ListBuilder) IsEmpty 

func (lb *ListBuilder) IsEmpty() bool

IsEmpty returns true, if no element was added.

func (*ListBuilder) List 

func (lb *ListBuilder) List() *Pair

List the result, resetting the builder.

func (*ListBuilder) Reset 

func (lb *ListBuilder) Reset()

Reset the list builder.

type Number 

type Number interface {
	Object

	// Returns true iff the number is equal to zero.
	IsZero() bool
}

Number value store numbers.

func GetNumber 

func GetNumber(obj Object) (Number, bool)

GetNumber returns the object as a number, if possible.

func NumAdd 

func NumAdd(x, y Number) Number

NumAdd adds the two numbers.

func NumDiv 

func NumDiv(x, y Number) (Number, error)

NumDiv divides the first by the second number.

func NumMod 

func NumMod(x, y Number) (Number, error)

NumMod divides the first by the second number.

func NumMul 

func NumMul(x, y Number) Number

NumMul multiplies the two numbers.

func NumNeg 

func NumNeg(x Number) Number

NumNeg negates the given number.

func NumSub 

func NumSub(x, y Number) Number

NumSub subtracts the two numbers.

func ParseInteger 

func ParseInteger(s string) (Number, error)

ParseInteger parses the string as an integer value and returns its value as a number.

type Object 

type Object interface {
	fmt.Stringer
	fmt.GoStringer

	// IsNil checks if the concrete object is nil.
	IsNil() bool

	// IsAtom returns true iff the object is an object that is not further decomposable.
	IsAtom() bool

	// IsEqual compare two objects for deep equality.
	IsEqual(Object) bool
}

Object is the generic value all s-expressions must fulfill.

func MakeBoolean 

func MakeBoolean(b bool) Object

MakeBoolean creates a new Boolean object.

type Pair 

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

Pair is a node containing a value for the element and a pointer to the tail. In other lisps it is often called "cell", "cons", "cons-cell", or "list".

func Cons 

func Cons(car, cdr Object) *Pair

func GetPair 

func GetPair(obj Object) (*Pair, bool)

GetPair returns the object as a pair.

func MakeList 

func MakeList(objs ...Object) *Pair

MakeList creates a new list with the given objects.

func Nil 

func Nil() *Pair

Nil() returns the nil list.

func (*Pair) AppendBang 

func (pair *Pair) AppendBang(obj Object) *Pair

AppendBang updates the given pair by setting a new pair with the given object and nil as its new second object.

func (*Pair) AsVector 

func (pair *Pair) AsVector() Vector

AsVector returns a proper list as a vector

func (*Pair) Assoc 

func (pair *Pair) Assoc(obj Object) *Pair

Assoc returns the first pair of a list where the car IsEqual to the given object.

func (*Pair) Car 

func (pair *Pair) Car() Object

Car returns the first object of a pair.

func (*Pair) Cdr 

func (pair *Pair) Cdr() Object

Cdr returns the second object of a pair.

func (*Pair) Cons 

func (pair *Pair) Cons(car Object) *Pair

Cons prepends a value in front of a given listreturning the new list.

func (*Pair) Copy 

func (pair *Pair) Copy() *Pair

Copy returns a copy of the given pair list.

func (*Pair) ExtendBang 

func (pair *Pair) ExtendBang(obj *Pair) *Pair

ExtendBang updates the given pair by extending it with the second pair list after its end. Returns the last list node of the newly formed list beginning with `lst`, which is also the last list node of the list starting with `val`.

func (*Pair) GoString 

func (pair *Pair) GoString() string

GoString returns the go string representation.

func (*Pair) Head 

func (pair *Pair) Head() *Pair

Head returns the first object as a pair, if possible. Otherwise it returns nil.

func (*Pair) IsAtom 

func (pair *Pair) IsAtom() bool

func (*Pair) IsEqual 

func (pair *Pair) IsEqual(other Object) bool

IsEqual compare two objects.

func (*Pair) IsNil 

func (pair *Pair) IsNil() bool

IsNil return true, if it is a nil pair object.

func (*Pair) Iterator 

func (pair *Pair) Iterator() SequenceIterator

func (*Pair) Last 

func (pair *Pair) Last() (Object, error)

Last returns the last element of a non-empty list.

func (*Pair) LastPair 

func (pair *Pair) LastPair() *Pair

LastPair returns the last pair of the given pair list, or nil.

func (*Pair) Length 

func (pair *Pair) Length() int

func (*Pair) LengthEqual 

func (pair *Pair) LengthEqual(n int) bool

func (*Pair) LengthGreater 

func (pair *Pair) LengthGreater(n int) bool

func (*Pair) LengthLess 

func (pair *Pair) LengthLess(n int) bool

func (*Pair) MakeList 

func (pair *Pair) MakeList() *Pair

func (*Pair) Nth 

func (pair *Pair) Nth(n int) (Object, error)

func (*Pair) Print 

func (pair *Pair) Print(w io.Writer) (int, error)

Print write the string representation to the given Writer.

func (*Pair) RemoveAssoc 

func (pair *Pair) RemoveAssoc(obj Object) *Pair

RemoveAssoc deletes all pairs from the association list, where the car IsEqual to the given object. A new list is created.

func (*Pair) Reverse 

func (pair *Pair) Reverse() (*Pair, error)

Reverse returns a reversed pair list.

func (*Pair) SetCar 

func (pair *Pair) SetCar(obj Object)

SetCar sets the car of the pair to the given object.

func (*Pair) SetCdr 

func (pair *Pair) SetCdr(obj Object)

SetCdr sets the cdr of the pair to the given object.

func (*Pair) String 

func (pair *Pair) String() string

String returns the string representation.

func (*Pair) Tail 

func (pair *Pair) Tail() *Pair

Tail returns the second object as a pair, if possible. Otherwise it returns nil.

type Printable 

type Printable interface {
	// Print emits the string representation on the given Writer
	Print(io.Writer) (int, error)
}

Printable is a object that has is specific representation, which is different to String().

type Sequence 

type Sequence interface {
	Object

	// Length returns the length of the sequence.
	Length() int

	// LengthLess reports whether the length of the sequence is less than
	// the given number.
	LengthLess(n int) bool

	// LengthGreater reports whether the length of the sequence is greater than
	// the given number.
	LengthGreater(n int) bool

	// LengthEqual reports whether the length of the sequence is equal to the
	// given number.
	LengthEqual(n int) bool

	// Nth returns the n-th element of a sequence.
	Nth(n int) (Object, error)

	// MakeList returns the sequence as a pair list. If sequence is already a
	// pair list, it is returned without copying it.
	MakeList() *Pair

	// Iterator return an SequenceIterator to iterate over all elements of
	// the sequence in natural order.
	Iterator() SequenceIterator
}

Sequence is an Object that has a finite, ordered set of elements.

func GetSequence 

func GetSequence(obj Object) (Sequence, bool)

GetSequence returns the object as a Sequence, if possible.

type SequenceIterator 

type SequenceIterator interface {
	// HasElement returns true if the iterator is able to return an element.
	HasElement() bool

	// Element returns the current element, or Undefined{} if there is no such element.
	Element() Object

	// Advance moves to the next element and return true if there is one.
	Advance() bool
}

SequenceIterator allows to iterate over all elements of a Sequence.

type String 

type String string

String represents a string object.

func GetString 

func GetString(obj Object) (String, bool)

GetString returns the object as a string, if possible

func (String) GoString 

func (s String) GoString() string

GoString returns the go string representation.

func (String) IsAtom 

func (String) IsAtom() bool

func (String) IsEqual 

func (s String) IsEqual(other Object) bool

IsEqual compares two objects for equivalence.

func (String) IsNil 

func (String) IsNil() bool

IsNil return true, if it is a nil string value.

func (String) Print 

func (s String) Print(w io.Writer) (int, error)

Print write the string representation to the given Writer.

func (String) String 

func (s String) String() string

String returns the string representation.

type Symbol 

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

Symbol represent a symbol value.

func GetSymbol 

func GetSymbol(obj Object) (*Symbol, bool)

GetSymbol returns the object as a symbol if possible.

func MakeSymbol 

func MakeSymbol(val string) *Symbol

MakeSymbol creates a symbol from a string.

func (*Symbol) GetValue 

func (sym *Symbol) GetValue() string

GetValue return the string value of the symbol.

func (*Symbol) GoString 

func (sy *Symbol) GoString() string

GoString returns the go string representation.

func (*Symbol) IsAtom 

func (*Symbol) IsAtom() bool

func (*Symbol) IsEqual 

func (sy *Symbol) IsEqual(other Object) bool

IsEqual compare two symbols.

func (*Symbol) IsNil 

func (sy *Symbol) IsNil() bool

IsNil may return true if a symbol pointer is nil.

func (*Symbol) Print 

func (sy *Symbol) Print(w io.Writer) (int, error)

Print write the string representation to the given Writer.

func (*Symbol) String 

func (sy *Symbol) String() string

String returns the string representation.

type Undefined 

type Undefined struct{}

Undefined is an object that signal a 'no value'.

func MakeUndefined 

func MakeUndefined() Undefined

MakeUndefined creates an undefined objact.

func (Undefined) GoString 

func (udef Undefined) GoString() string

func (Undefined) IsAtom 

func (Undefined) IsAtom() bool

func (Undefined) IsEqual 

func (Undefined) IsEqual(other Object) bool

func (Undefined) IsNil 

func (Undefined) IsNil() bool

func (Undefined) String 

func (Undefined) String() string

type Vector 

type Vector []Object

Vector is a sequence of Objects.

func GetVector 

func GetVector(obj Object) (Vector, bool)

GetVector returns the object as a vector, if possible.

func (Vector) GoString 

func (v Vector) GoString() string

func (Vector) IsAtom 

func (v Vector) IsAtom() bool

func (Vector) IsEqual 

func (v Vector) IsEqual(other Object) bool

func (Vector) IsNil 

func (v Vector) IsNil() bool

func (Vector) Iterator 

func (v Vector) Iterator() SequenceIterator

func (Vector) Length 

func (v Vector) Length() int

func (Vector) LengthEqual 

func (v Vector) LengthEqual(n int) bool

func (Vector) LengthGreater 

func (v Vector) LengthGreater(n int) bool

func (Vector) LengthLess 

func (v Vector) LengthLess(n int) bool

func (Vector) MakeList 

func (v Vector) MakeList() *Pair

func (Vector) Nth 

func (v Vector) Nth(n int) (Object, error)

func (Vector) Print 

func (v Vector) Print(w io.Writer) (int, error)

Print write the string representation to the given Writer.

func (Vector) String 

func (v Vector) String() string

Source Files

  • boolean.go
  • const.go
  • list.go
  • number.go
  • sequence.go
  • string.go
  • sx.go
  • symbol.go
  • undef.go
  • vector.go

Directories

Path Synopsis
Package sxbuiltins contains functions that help to build builtin functions.
 Package sxbuiltins contains functions that help to build builtin functions.
Package sxeval allows to evaluate s-expressions.
 Package sxeval allows to evaluate s-expressions.
Package sxhtml represents HTML as s-expressions.
 Package sxhtml represents HTML as s-expressions.

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