expressions

Documentation

Overview

Package expressions is an internal package that parses and evaluates the expression language.

This is the language that is used inside Liquid object and tags; e.g. "a.b[c]" in {{ a.b[c] }}, and "pages = site.pages | reverse" in {% assign pages = site.pages | reverse %}.

Index

• Constants
• func EvaluateString(source string, ctx Context) (any, error)
• type Assignment
• type Closure
• type Config
  • func NewConfig() Config
  • func (c *Config) AddFilter(name string, fn any)
• type Context
  • func NewContext(vars map[string]any, cfg Config) Context
• type Cycle
• type Expression
  • func Constant(k any) Expression
  • func Not(e Expression) Expression
  • func Parse(source string) (expr Expression, err error)
• type FilterError
  • func (e FilterError) Error() string
• type InterpreterError
  • func (e InterpreterError) Error() string
• type Loop
• type Statement
  • func ParseStatement(sel, source string) (*Statement, error)
• type SyntaxError
  • func (e SyntaxError) Error() string
• type UndefinedFilter
  • func (e UndefinedFilter) Error() string
• type When

Constants

const (
	AssignStatementSelector = "%assign "
	CycleStatementSelector  = "{%cycle "
	LoopStatementSelector   = "%loop "
	WhenStatementSelector   = "{%when "
)

These strings match lexer tokens.

const AND = 57359

const ASSIGN = 57350

const CONTAINS = 57361

const CYCLE = 57351

const DOTDOT = 57362

const EQ = 57354

const GE = 57356

const IDENTIFIER = 57347

const IN = 57358

const KEYWORD = 57348

const LE = 57357

const LITERAL = 57346

const LOOP = 57352

const NEQ = 57355

const OR = 57360

const PROPERTY = 57349

const WHEN = 57353

Functions

func EvaluateString

func EvaluateString(source string, ctx Context) (any, error)

EvaluateString is a wrapper for Parse and Evaluate.

Types

type Assignment

type Assignment struct {
	Variable string
	ValueFn  Expression
}

An Assignment is a parse of an {% assign %} statement

type Closure

type Closure interface {
	// Bind creates a new closure with a new binding.
	Bind(name string, value any) Closure
	Evaluate() (any, error)
}

A Closure is an expression within a lexical environment. A closure may refer to variables that are not defined in the environment. (Therefore it's not a technically a closure.)

type Config

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

Config holds configuration information for expression interpretation.

func NewConfig

func NewConfig() Config

NewConfig creates a new Config.

func (*Config) AddFilter

func (c *Config) AddFilter(name string, fn any)

AddFilter adds a filter to the filter dictionary.

type Context

type Context interface {
	ApplyFilter(string, valueFn, []valueFn) (any, error)
	// Clone returns a copy with a new variable binding map
	// (so that copy.Set does effect the source context.)
	Clone() Context
	Get(string) any
	Set(string, any)
}

Context is the expression evaluation context. It maps variables names to values.

func NewContext

func NewContext(vars map[string]any, cfg Config) Context

NewContext makes a new expression evaluation context.

type Cycle

type Cycle struct {
	Group  string
	Values []string
}

A Cycle is a parse of an {% assign %} statement

type Expression

type Expression interface {
	// Evaluate evaluates an expression in a context.
	Evaluate(ctx Context) (any, error)
}

An Expression is a compiled expression.

func Constant

func Constant(k any) Expression

Constant creates an expression that returns a constant value.

func Not

func Not(e Expression) Expression

Not creates an expression that returns ! of the wrapped expression.

func Parse

func Parse(source string) (expr Expression, err error)

Parse parses an expression string into an Expression.

type FilterError

type FilterError struct {
	FilterName string
	Err        error
}

FilterError is the error returned by a filter when it is applied

func (FilterError) Error

func (e FilterError) Error() string

type InterpreterError

type InterpreterError string

An InterpreterError is an error during expression interpretation. It is used for errors in the input expression, to distinguish them from implementation errors in the interpreter.

func (InterpreterError) Error

func (e InterpreterError) Error() string

type Loop

type Loop struct {
	Variable string
	Expr     Expression
	// contains filtered or unexported fields
}

A Loop is a parse of a {% loop %} statement

type Statement

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

A Statement is the result of parsing a string.

func ParseStatement

func ParseStatement(sel, source string) (*Statement, error)

ParseStatement parses an statement into an Expression that can evaluated to return a structure specific to the statement.

type SyntaxError

type SyntaxError string

SyntaxError represents a syntax error. The yacc-generated compiler doesn't use error returns; this lets us recognize them.

func (SyntaxError) Error

func (e SyntaxError) Error() string

type UndefinedFilter

type UndefinedFilter string

UndefinedFilter is an error that the named filter is not defined.

func (UndefinedFilter) Error

func (e UndefinedFilter) Error() string

type When

type When struct {
	Exprs []Expression
}

A When is a parse of a {% when %} clause