lep

package module
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 Go to latest Published: Sep 4, 2023 License: MIT Imports: 16 Imported by: 0

README

logic-expression-parser

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This library provide generic boolean expression parser to go structures.

Installation

$ go get -u github.com/solo-finance/logic-expression-parser

(optional) Run unit tests

$ make test

(optional) Run benchmarks

$ make bench

Examples

package main

import (
	"github.com/davecgh/go-spew/spew"
	lep "github.com/mgudov/logic-expression-parser"
)

func main() {
	expression := `a=false && b>=c && (d<1000 || e in [1,2,3])`

	result, err := lep.ParseExpression(expression)
	if err != nil {
		panic(err)
	}

	dump := spew.NewDefaultConfig()
	dump.DisablePointerAddresses = true
	dump.DisableMethods = true
	dump.Dump(result)
}

This library would parse the expression and return the following struct:

(*lep.AndX)({
  Conjuncts: ([]lep.Expression) (len=3 cap=4) {
    (*lep.EqualsX)({
      Param: (*lep.ParamX)({
        Name: (string) (len=1) "a"
      }),
      Value: (*lep.BooleanX)({
        Val: (bool) false
      })
    }),
    (*lep.GreaterThanEqualX)({
      Param: (*lep.ParamX)({
        Name: (string) (len=1) "b"
      }),
      Value: (*lep.ParamX)({
        Name: (string) (len=1) "c"
      })
    }),
    (*lep.OrX)({
      Disjunctions: ([]lep.Expression) (len=2 cap=2) {
        (*lep.LessThanX)({
          Param: (*lep.ParamX)({
            Name: (string) (len=1) "d"
          }),
          Value: (*lep.IntegerX)({
            Val: (int64) 1000
          })
        }),
        (*lep.InSliceX)({
          Param: (*lep.ParamX)({
            Name: (string) (len=1) "e"
          }),
          Slice: (*lep.SliceX)({
            Values: ([]lep.Value) (len=3 cap=4) {
              (*lep.IntegerX)({
                Val: (int64) 1
              }),
              (*lep.IntegerX)({
                Val: (int64) 2
              }),
              (*lep.IntegerX)({
                Val: (int64) 3
              })
            }
          })
        })
      }
    })
  }
})

Use can also create expression string from code:

package main

import (
	"fmt"
	lep "github.com/mgudov/logic-expression-parser"
)

func main() {
	expression := lep.And(
		lep.Equals(lep.Param("a"), lep.Boolean(false)),
		lep.GreaterThanEqual(lep.Param("b"), lep.Param("c")),
		lep.Or(
			lep.LessThan(lep.Param("d"), lep.Integer(1000)),
			lep.InSlice(
				lep.Param("e"),
				lep.Slice(lep.Integer(1), lep.Integer(2), lep.Integer(3)),
			),
		),
	)

	fmt.Println(expression.String())
}

a=false && b>=c && (d<1000 || e in [1,2,3])

Real life examples

Create SQL query from expression string 
package main

import (
	"fmt"
	"github.com/davecgh/go-spew/spew"
	sb "github.com/huandu/go-sqlbuilder"
	lep "github.com/mgudov/logic-expression-parser"
)

func traverse(sql *sb.SelectBuilder, expr lep.Expression) (string, error) {
	switch e := expr.(type) {
	default:
		return "", fmt.Errorf("not implemented: %T", e)
	case *lep.OrX:
		var args []string
		for _, disjunction := range e.Disjunctions {
			arg, err := traverse(sql, disjunction)
			if err != nil {
				return "", err
			}
			args = append(args, arg)
		}
		return sql.Or(args...), nil
	case *lep.AndX:
		var args []string
		for _, conjunct := range e.Conjuncts {
			arg, err := traverse(sql, conjunct)
			if err != nil {
				return "", err
			}
			args = append(args, arg)
		}
		return sql.And(args...), nil
	case *lep.EqualsX:
		value := e.Value.Value()
		if value == nil {
			return sql.IsNotNull(e.Param.String()), nil
		}
		return sql.Equal(e.Param.String(), value), nil
	case *lep.NotEqualsX:
		value := e.Value.Value()
		if value == nil {
			return sql.IsNotNull(e.Param.String()), nil
		}
		return sql.NotEqual(e.Param.String(), value), nil
	case *lep.GreaterThanX:
		return sql.GreaterThan(e.Param.String(), e.Value.Value()), nil
	case *lep.InSliceX:
		var items []interface{}
		for _, value := range e.Slice.Values {
			items = append(items, value.Value())
		}
		return sql.In(e.Param.String(), items...), nil

		// TODO: other cases
	}
}

func main() {
	query := `active=true && email!=null && (last_login>dt:"2010-01-01" || role in ["client","customer"])`

	expr, err := lep.ParseExpression(query)
	if err != nil {
		panic(err)
	}

	sql := sb.Select("*").From("users")
	where, err := traverse(sql, expr)
	if err != nil {
		panic(err)
	}
	sql.Where(where)

	spew.Dump(sql.Build())
}

(string) (len=99) "SELECT * FROM users WHERE (active = ? AND email IS NOT NULL AND (last_login > ? OR role IN (?, ?)))"
([]interface {}) (len=4 cap=4) {
 (bool) true,
 (time.Time) 2010-01-01 00:00:00 +0000 UTC,
 (string) (len=6) "client",
 (string) (len=8) "customer"
}

Operators and types

  • Comparators: = != > >= < <= (left - param, right - param or value)
  • Logical operations: || && (left, right - any statements)
  • Numeric constants: integer 64-bit (12345678), float 64-bit with floating point (12345.678)
  • String constants (double quotes: "foo bar", "foo "bar"")
  • String operations: starts_with, ends_with (left - param, right - param or string)
  • Regexp operations: =~ (match regexp a =~ /[a-z]+/), !~ (not match b !~ /[0-9]+/)
  • Date constants (double quotes after dt:): dt:"2020-03-04 10:20:30" (for parsing datetime used dateparse)
  • Arrays (any values separated by , within square bracket: [1,2,"foo",dt:"1999-09-09"])
  • Array operations: in not_in (a in [1,2,3])
  • Boolean constants: true false
  • Null constant: null

Benchmarks

Here are the results output from a benchmark run on a Macbook Pro 2018:

go test -benchmem -bench=.
goos: darwin
goarch: amd64
pkg: github.com/mgudov/logic-expression-parser
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
BenchmarkSmallQuery-16                     26547             45293 ns/op           19353 B/op        332 allocs/op
BenchmarkMediumQuery-16                    10000            106334 ns/op           42931 B/op        807 allocs/op
BenchmarkLargeQuery-16                      3268            331438 ns/op          114500 B/op       2385 allocs/op
BenchmarkSmallQueryWithMemo-16             14696             79791 ns/op           82590 B/op        276 allocs/op
BenchmarkMediumQueryWithMemo-16             4924            246504 ns/op          257072 B/op        746 allocs/op
BenchmarkLargeQueryWithMemo-16              2071            590092 ns/op          594584 B/op       1627 allocs/op
PASS
ok      github.com/mgudov/logic-expression-parser       8.744s

Used Libraries

For parsing string the pigeon parser generator is used (Licensed under BSD 3-Clause).

Documentation

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

func IncorrectType 

func IncorrectType(funcName string, expected, received interface{}) error

func IncorrectValue 

func IncorrectValue(funcName string, expected, received interface{}) error

func Parse 

func Parse(filename string, b []byte, opts ...Option) (interface{}, error)

Parse parses the data from b using filename as information in the error messages.

func ParseFile 

func ParseFile(filename string, opts ...Option) (i interface{}, err error)

ParseFile parses the file identified by filename.

func ParseReader 

func ParseReader(filename string, r io.Reader, opts ...Option) (interface{}, error)

ParseReader parses the data from r using filename as information in the error messages.

Types

type AndX 

type AndX struct {
	Conjuncts []Expression
}

func And 

func And(expr ...Expression) *AndX

func (AndX) Equals 

func (e AndX) Equals(other Expression) bool

func (AndX) String 

func (e AndX) String() string

type Between 

type Between struct {
	Start Value
	End   Value
	// contains filtered or unexported fields
}

func BetweenXandY 

func BetweenXandY(param *ParamX, start Value, end Value) *Between

func (Between) Equals 

func (s Between) Equals(other Expression) bool

func (Between) GetParam 

func (s Between) GetParam() *ParamX

func (Between) GetValue 

func (s Between) GetValue() Value

func (Between) String 

func (s Between) String() string

type BooleanX 

type BooleanX struct {
	Val bool
}

func Boolean 

func Boolean(val bool) *BooleanX

func (BooleanX) Equals 

func (v BooleanX) Equals(other Expression) bool

func (BooleanX) String 

func (v BooleanX) String() string

func (BooleanX) Value 

func (v BooleanX) Value() interface{}

type Cloner 

type Cloner interface {
	Clone() interface{}
}

Cloner is implemented by any value that has a Clone method, which returns a copy of the value. This is mainly used for types which are not passed by value (e.g map, slice, chan) or structs that contain such types.

This is used in conjunction with the global state feature to create proper copies of the state to allow the parser to properly restore the state in the case of backtracking.

type DateTimeX 

type DateTimeX struct {
	Val    time.Time
	Format string
}

func DateTime 

func DateTime(dt time.Time, format string) *DateTimeX

func (DateTimeX) Equals 

func (v DateTimeX) Equals(other Expression) bool

func (DateTimeX) String 

func (v DateTimeX) String() string

func (DateTimeX) Value 

func (v DateTimeX) Value() interface{}

type EndsWithX 

type EndsWithX struct {
	Param *ParamX
	Value Stringify
}

func EndsWith 

func EndsWith(param *ParamX, value Stringify) *EndsWithX

func (EndsWithX) Equals 

func (e EndsWithX) Equals(other Expression) bool

func (EndsWithX) GetParam 

func (e EndsWithX) GetParam() *ParamX

func (EndsWithX) GetValue 

func (e EndsWithX) GetValue() Value

func (EndsWithX) String 

func (e EndsWithX) String() string

type EqualsX 

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

func Equals 

func Equals(param *ParamX, value Value) *EqualsX

func (EqualsX) Equals 

func (e EqualsX) Equals(other Expression) bool

func (EqualsX) GetParam 

func (s EqualsX) GetParam() *ParamX

func (EqualsX) GetValue 

func (s EqualsX) GetValue() Value

func (EqualsX) String 

func (e EqualsX) String() string

type ErrIncorrectType 

type ErrIncorrectType struct {
	FuncName string
	Expected interface{}
	Received interface{}
}

func (ErrIncorrectType) Error 

func (e ErrIncorrectType) Error() string

type ErrIncorrectValue 

type ErrIncorrectValue struct {
	FuncName string
	Expected interface{}
	Received interface{}
}

func (ErrIncorrectValue) Error 

func (e ErrIncorrectValue) Error() string

type Expression 

type Expression interface {
	Equals(Expression) bool
	String() string
}

func ParseExpression 

func ParseExpression(data string, opts ...Option) (Expression, error)

type FloatX 

type FloatX struct {
	Val float64
}

func Float 

func Float(val float64) *FloatX

func (FloatX) Equals 

func (f FloatX) Equals(other Expression) bool

func (FloatX) String 

func (f FloatX) String() string

func (FloatX) Value 

func (f FloatX) Value() interface{}

type GreaterThanEqualX 

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

func GreaterThanEqual 

func GreaterThanEqual(param *ParamX, value Value) *GreaterThanEqualX

func (GreaterThanEqualX) Equals 

func (s GreaterThanEqualX) Equals(other Expression) bool

func (GreaterThanEqualX) GetParam 

func (s GreaterThanEqualX) GetParam() *ParamX

func (GreaterThanEqualX) GetValue 

func (s GreaterThanEqualX) GetValue() Value

func (GreaterThanEqualX) String 

func (s GreaterThanEqualX) String() string

type GreaterThanX 

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

func GreaterThan 

func GreaterThan(param *ParamX, value Value) *GreaterThanX

func (GreaterThanX) Equals 

func (s GreaterThanX) Equals(other Expression) bool

func (GreaterThanX) GetParam 

func (s GreaterThanX) GetParam() *ParamX

func (GreaterThanX) GetValue 

func (s GreaterThanX) GetValue() Value

func (GreaterThanX) String 

func (s GreaterThanX) String() string

type HasAllX 

type HasAllX struct {
	Param *ParamX
	Slice *SliceX
}

func HasAll 

func HasAll(param *ParamX, slice *SliceX) *HasAllX

func (HasAllX) Equals 

func (e HasAllX) Equals(other Expression) bool

func (HasAllX) GetParam 

func (e HasAllX) GetParam() *ParamX

func (HasAllX) GetValue 

func (e HasAllX) GetValue() Value

func (HasAllX) String 

func (e HasAllX) String() string

type HasAnyX 

type HasAnyX struct {
	Param *ParamX
	Slice *SliceX
}

func HasAny 

func HasAny(param *ParamX, slice *SliceX) *HasAnyX

func (HasAnyX) Equals 

func (e HasAnyX) Equals(other Expression) bool

func (HasAnyX) GetParam 

func (e HasAnyX) GetParam() *ParamX

func (HasAnyX) GetValue 

func (e HasAnyX) GetValue() Value

func (HasAnyX) String 

func (e HasAnyX) String() string

type HasX 

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

func Has 

func Has(param *ParamX, value Value) *HasX

func (HasX) Equals 

func (e HasX) Equals(other Expression) bool

func (HasX) GetParam 

func (s HasX) GetParam() *ParamX

func (HasX) GetValue 

func (s HasX) GetValue() Value

func (HasX) String 

func (e HasX) String() string

type InSliceX 

type InSliceX struct {
	Param *ParamX
	Slice *SliceX
}

func InSlice 

func InSlice(param *ParamX, slice *SliceX) *InSliceX

func (InSliceX) Equals 

func (e InSliceX) Equals(other Expression) bool

func (InSliceX) GetParam 

func (e InSliceX) GetParam() *ParamX

func (InSliceX) GetValue 

func (e InSliceX) GetValue() Value

func (InSliceX) String 

func (e InSliceX) String() string

type IntegerX 

type IntegerX struct {
	Val int64
}

func Integer 

func Integer(val int64) *IntegerX

func (IntegerX) Equals 

func (i IntegerX) Equals(other Expression) bool

func (IntegerX) String 

func (i IntegerX) String() string

func (IntegerX) Value 

func (i IntegerX) Value() interface{}

type LessThanEqualX 

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

func LessThanEqual 

func LessThanEqual(param *ParamX, value Value) *LessThanEqualX

func (LessThanEqualX) Equals 

func (s LessThanEqualX) Equals(other Expression) bool

func (LessThanEqualX) GetParam 

func (s LessThanEqualX) GetParam() *ParamX

func (LessThanEqualX) GetValue 

func (s LessThanEqualX) GetValue() Value

func (LessThanEqualX) String 

func (s LessThanEqualX) String() string

type LessThanX 

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

func LessThan 

func LessThan(param *ParamX, value Value) *LessThanX

func (LessThanX) Equals 

func (s LessThanX) Equals(other Expression) bool

func (LessThanX) GetParam 

func (s LessThanX) GetParam() *ParamX

func (LessThanX) GetValue 

func (s LessThanX) GetValue() Value

func (LessThanX) String 

func (s LessThanX) String() string

type LikeX 

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

func Like 

func Like(param *ParamX, value Value) *LikeX

func (LikeX) Equals 

func (e LikeX) Equals(other Expression) bool

func (LikeX) GetParam 

func (s LikeX) GetParam() *ParamX

func (LikeX) GetValue 

func (s LikeX) GetValue() Value

func (LikeX) String 

func (e LikeX) String() string

type MatchRegexpX 

type MatchRegexpX struct {
	Param  *ParamX
	Regexp *RegexpX
}

func MatchRegexp 

func MatchRegexp(param *ParamX, regexp *RegexpX) *MatchRegexpX

func (MatchRegexpX) Equals 

func (e MatchRegexpX) Equals(other Expression) bool

func (MatchRegexpX) GetParam 

func (e MatchRegexpX) GetParam() *ParamX

func (MatchRegexpX) GetValue 

func (e MatchRegexpX) GetValue() Value

func (MatchRegexpX) String 

func (e MatchRegexpX) String() string

type NotEqualsX 

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

func NotEquals 

func NotEquals(param *ParamX, value Value) *NotEqualsX

func (NotEqualsX) Equals 

func (e NotEqualsX) Equals(other Expression) bool

func (NotEqualsX) GetParam 

func (s NotEqualsX) GetParam() *ParamX

func (NotEqualsX) GetValue 

func (s NotEqualsX) GetValue() Value

func (NotEqualsX) String 

func (e NotEqualsX) String() string

type NotHasX 

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

func NotHas 

func NotHas(param *ParamX, value Value) *NotHasX

func (NotHasX) Equals 

func (e NotHasX) Equals(other Expression) bool

func (NotHasX) GetParam 

func (s NotHasX) GetParam() *ParamX

func (NotHasX) GetValue 

func (s NotHasX) GetValue() Value

func (NotHasX) String 

func (e NotHasX) String() string

type NotInSliceX 

type NotInSliceX struct {
	Param *ParamX
	Slice *SliceX
}

func NotInSlice 

func NotInSlice(param *ParamX, slice *SliceX) *NotInSliceX

func (NotInSliceX) Equals 

func (e NotInSliceX) Equals(other Expression) bool

func (NotInSliceX) GetParam 

func (e NotInSliceX) GetParam() *ParamX

func (NotInSliceX) GetValue 

func (e NotInSliceX) GetValue() Value

func (NotInSliceX) String 

func (e NotInSliceX) String() string

type NotLikeX 

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

func NotLike 

func NotLike(param *ParamX, value Value) *NotLikeX

func (NotLikeX) Equals 

func (e NotLikeX) Equals(other Expression) bool

func (NotLikeX) GetParam 

func (s NotLikeX) GetParam() *ParamX

func (NotLikeX) GetValue 

func (s NotLikeX) GetValue() Value

func (NotLikeX) String 

func (e NotLikeX) String() string

type NotMatchRegexpX 

type NotMatchRegexpX struct {
	Param  *ParamX
	Regexp *RegexpX
}

func NotMatchRegexp 

func NotMatchRegexp(param *ParamX, regexp *RegexpX) *NotMatchRegexpX

func (NotMatchRegexpX) Equals 

func (e NotMatchRegexpX) Equals(other Expression) bool

func (NotMatchRegexpX) GetParam 

func (e NotMatchRegexpX) GetParam() *ParamX

func (NotMatchRegexpX) GetValue 

func (e NotMatchRegexpX) GetValue() Value

func (NotMatchRegexpX) String 

func (e NotMatchRegexpX) String() string

type NullX 

type NullX struct{}

func Null 

func Null() *NullX

func (NullX) Equals 

func (NullX) Equals(other Expression) bool

func (NullX) String 

func (NullX) String() string

func (NullX) Value 

func (NullX) Value() interface{}

type Option 

type Option func(*parser) Option

Option is a function that can set an option on the parser. It returns the previous setting as an Option.

func AllowInvalidUTF8 

func AllowInvalidUTF8(b bool) Option

AllowInvalidUTF8 creates an Option to allow invalid UTF-8 bytes. Every invalid UTF-8 byte is treated as a utf8.RuneError (U+FFFD) by character class matchers and is matched by the any matcher. The returned matched value, c.text and c.offset are NOT affected.

The default is false.

func Debug 

func Debug(b bool) Option

Debug creates an Option to set the debug flag to b. When set to true, debugging information is printed to stdout while parsing.

The default is false.

func Entrypoint 

func Entrypoint(ruleName string) Option

Entrypoint creates an Option to set the rule name to use as entrypoint. The rule name must have been specified in the -alternate-entrypoints if generating the parser with the -optimize-grammar flag, otherwise it may have been optimized out. Passing an empty string sets the entrypoint to the first rule in the grammar.

The default is to start parsing at the first rule in the grammar.

func GlobalStore 

func GlobalStore(key string, value interface{}) Option

GlobalStore creates an Option to set a key to a certain value in the globalStore.

func InitState 

func InitState(key string, value interface{}) Option

InitState creates an Option to set a key to a certain value in the global "state" store.

func MaxExpressions 

func MaxExpressions(maxExprCnt uint64) Option

MaxExpressions creates an Option to stop parsing after the provided number of expressions have been parsed, if the value is 0 then the parser will parse for as many steps as needed (possibly an infinite number).

The default for maxExprCnt is 0.

func Memoize 

func Memoize(b bool) Option

Memoize creates an Option to set the memoize flag to b. When set to true, the parser will cache all results so each expression is evaluated only once. This guarantees linear parsing time even for pathological cases, at the expense of more memory and slower times for typical cases.

The default is false.

func Recover 

func Recover(b bool) Option

Recover creates an Option to set the recover flag to b. When set to true, this causes the parser to recover from panics and convert it to an error. Setting it to false can be useful while debugging to access the full stack trace.

The default is true.

func Statistics 

func Statistics(stats *Stats, choiceNoMatch string) Option

Statistics adds a user provided Stats struct to the parser to allow the user to process the results after the parsing has finished. Also the key for the "no match" counter is set.

Example usage: 

input := "input"
stats := Stats{}
_, err := Parse("input-file", []byte(input), Statistics(&stats, "no match"))
if err != nil {
    log.Panicln(err)
}
b, err := json.MarshalIndent(stats.ChoiceAltCnt, "", "  ")
if err != nil {
    log.Panicln(err)
}
fmt.Println(string(b))

type OrX 

type OrX struct {
	Disjunctions []Expression
}

func Or 

func Or(expr ...Expression) *OrX

func (OrX) Equals 

func (e OrX) Equals(other Expression) bool

func (OrX) String 

func (e OrX) String() string

type ParamX 

type ParamX struct {
	Name string
}

func Param 

func Param(name string) *ParamX

func (ParamX) Equals 

func (p ParamX) Equals(other Expression) bool

func (ParamX) IsStringify 

func (p ParamX) IsStringify() bool

func (ParamX) String 

func (p ParamX) String() string

func (ParamX) Value 

func (p ParamX) Value() interface{}

type RegexpX 

type RegexpX struct {
	Regexp *regexp.Regexp
}

func Regexp 

func Regexp(regexp *regexp.Regexp) *RegexpX

func (RegexpX) Equals 

func (e RegexpX) Equals(other Expression) bool

func (RegexpX) String 

func (e RegexpX) String() string

func (RegexpX) Value 

func (e RegexpX) Value() interface{}

type SliceX 

type SliceX struct {
	Values []Value
}

func Slice 

func Slice(values ...Value) *SliceX

func (SliceX) Equals 

func (e SliceX) Equals(other Expression) bool

func (SliceX) String 

func (e SliceX) String() string

func (SliceX) Value 

func (e SliceX) Value() interface{}

type StartsWithX 

type StartsWithX struct {
	Param *ParamX
	Value Stringify
}

func StartsWith 

func StartsWith(param *ParamX, value Stringify) *StartsWithX

func (StartsWithX) Equals 

func (e StartsWithX) Equals(other Expression) bool

func (StartsWithX) GetParam 

func (e StartsWithX) GetParam() *ParamX

func (StartsWithX) GetValue 

func (e StartsWithX) GetValue() Value

func (StartsWithX) String 

func (e StartsWithX) String() string

type Statement 

type Statement interface {
	GetParam() *ParamX
	GetValue() Value
}

type Stats 

type Stats struct {
	// ExprCnt counts the number of expressions processed during parsing
	// This value is compared to the maximum number of expressions allowed
	// (set by the MaxExpressions option).
	ExprCnt uint64

	// ChoiceAltCnt is used to count for each ordered choice expression,
	// which alternative is used how may times.
	// These numbers allow to optimize the order of the ordered choice expression
	// to increase the performance of the parser
	//
	// The outer key of ChoiceAltCnt is composed of the name of the rule as well
	// as the line and the column of the ordered choice.
	// The inner key of ChoiceAltCnt is the number (one-based) of the matching alternative.
	// For each alternative the number of matches are counted. If an ordered choice does not
	// match, a special counter is incremented. The name of this counter is set with
	// the parser option Statistics.
	// For an alternative to be included in ChoiceAltCnt, it has to match at least once.
	ChoiceAltCnt map[string]map[string]int
}

Stats stores some statistics, gathered during parsing

type StringX 

type StringX struct {
	Val string
}

func String 

func String(val string) *StringX

func (StringX) Equals 

func (s StringX) Equals(other Expression) bool

func (StringX) IsStringify 

func (s StringX) IsStringify() bool

func (StringX) String 

func (s StringX) String() string

func (StringX) Value 

func (s StringX) Value() interface{}

type Stringify 

type Stringify interface {
	Value
	IsStringify() bool
}

type Value 

type Value interface {
	Expression
	Value() interface{}
}

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