parser

package
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 Go to latest Published: Jul 19, 2024 License: Apache-2.0 Imports: 5 Imported by: 0

Documentation

Overview

Package parser generates an AST for Evy programs.

First, Evy source code is tokenized by the lexer, then the generated tokens are parsed into an Abstract Syntax Tree (AST) by the Parse function. Finally, the evaluator walks the AST and executes the program. This package is concerned with the second step of parsing tokens into an AST.

Parsing

The Parse function in this package uses a top-down, recursive descent parsing approach. This means that parsing starts with the top-level structure of the program and recursively descends into its components.

Expression parsing is a particularly tricky part of the parsing process. Expressions are used in variable declarations, assignments, function calls, and many other places. Expressions are not simply evaluated top-down, left-to-right. For example, in the expression 2+3*4, the multiplication operator * has higher precedence than the addition operator +. This means that the expression 3*4 must be evaluated before the expression 2+3.

To handle expressions with different levels of precedence, the Parse function uses a Pratt parser. A Pratt parser is a type of top-down, recursive descent parser that can handle expressions with different levels of precedence.

Abstract Syntax Tree

The Abstract Syntax Tree (AST) is a hierarchical representation of an Evy program's structure. It is the result of the Parse function. It can be used for evaluation, further analysis, and code generation, such as formatted printing of the Evy source code with Program.Format. The AST consists of a tree of nodes, each of which implements the Node interface.

Each node in the AST represents a different element of the program's structure. The root node of the AST represents the entire Program. The root node's direct child nodes are block statements and basic statements.

Block statements contain further statements. They include:

  • FuncDefStmt: A statement that defines a function.
  • EventHandlerStmt: A statement that defines an event handler.
  • IfStmt: A statement that executes a block of code if a condition is met.
  • ForStmt: A statement that executes a block of code repeatedly.
  • WhileStmt: A statement that executes a block of code repeatedly while a condition is met.

Basic statements are statements that cannot be broken down into further statements. They include:

  • TypedDeclStmt: A statement that declares a variable of an explicitly specified type.
  • InferredDeclStmt: A statement that declares a variable with a type that is inferred from the value.
  • AssignmentStmt: A statement that assigns a value to a variable.
  • FuncCallStmt: A statement that calls a function.
  • ReturnStmt: A statement that returns from a function.
  • BreakStmt: A statement that breaks out of a loop.

The components of basic statements are:

Variables are named references to values. Literals are values that are directly represented in the Evy source code. Expressions are combinations of variables, literals, operators and function calls to form new values.

This structure closely resembles the grammar of the Evy programming language, as defined in the language specification.

Index

Constants

This section is empty.

Variables

View Source 
var (
	NUM_TYPE      = &Type{Name: NUM}
	BOOL_TYPE     = &Type{Name: BOOL}
	STRING_TYPE   = &Type{Name: STRING}
	ANY_TYPE      = &Type{Name: ANY}
	NONE_TYPE     = &Type{Name: NONE}
	EMPTY_ARRAY   = &Type{Name: ARRAY, Sub: NONE_TYPE}
	EMPTY_MAP     = &Type{Name: MAP, Sub: NONE_TYPE}
	GENERIC_ARRAY = &Type{Name: ARRAY}
	GENERIC_MAP   = &Type{Name: MAP}
)

Basic types, any, none, and untyped arrays and untyped maps are interned into variables for reuse, such as NUM_TYPE or EMPTY_MAP.

Functions

This section is empty.

Types

type Any added in v0.0.194 

type Any struct {
	Value Node
	// contains filtered or unexported fields
}

Any is an AST node that wraps literals and non-any variables if the target assignable requires it.

func (*Any) String added in v0.0.194 

func (a *Any) String() string

String returns a string representation of the Program node.

func (*Any) Token added in v0.0.194 

func (a *Any) Token() *lexer.Token

Token returns the token of the Evy source program associated with the Any node.

func (*Any) Type added in v0.0.194 

func (*Any) Type() *Type

Type always returns ANY_TYPE.

type ArrayLiteral 

type ArrayLiteral struct {
	Elements []Node
	T        *Type
	// contains filtered or unexported fields
}

ArrayLiteral is an AST node that represents an array literal, such as: [1 2 3].

ArrayLiteral implements the Node interface.

func (*ArrayLiteral) String 

func (a *ArrayLiteral) String() string

String returns a string representation of the ArrayLiteral node.

func (*ArrayLiteral) Token 

func (a *ArrayLiteral) Token() *lexer.Token

Token returns the token of the Evy source program associated with the ArrayLiteral node.

func (*ArrayLiteral) Type 

func (a *ArrayLiteral) Type() *Type

Type returns the type of the array literal, such as []num for [1 2 3].

type AssignmentStmt 

type AssignmentStmt struct {
	Target Node // Variable, index or field expression
	Value  Node // literal, expression, variable...
	// contains filtered or unexported fields
}

AssignmentStmt is an AST node that represents an assignment statement. An assignment statement assigns a value to a variable, such as n = 2.

AssignmentStmt implements the Node interface.

func (*AssignmentStmt) String 

func (a *AssignmentStmt) String() string

String returns a string representation of the AssignmentStmt node.

func (*AssignmentStmt) Token 

func (a *AssignmentStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the AssignmentStmt node.

func (*AssignmentStmt) Type 

func (a *AssignmentStmt) Type() *Type

Type returns the type of the variable that is assigned.

type BinaryExpression 

type BinaryExpression struct {
	T *Type

	Op    Operator
	Left  Node
	Right Node
	// contains filtered or unexported fields
}

BinaryExpression is an AST node that represents a binary expression. A binary expression is an expression that has two operands and an operator, such as a + b.

BinaryExpression implements the Node interface.

func (*BinaryExpression) String 

func (b *BinaryExpression) String() string

String returns a string representation of the BinaryExpression node.

func (*BinaryExpression) Token 

func (b *BinaryExpression) Token() *lexer.Token

Token returns the token of the Evy source program associated with the BinaryExpression node.

func (*BinaryExpression) Type 

func (b *BinaryExpression) Type() *Type

Type returns the type of the BinaryExpression, such as bool, num or string.

type BlockStatement 

type BlockStatement struct {
	Statements []Node
	// contains filtered or unexported fields
}

BlockStatement is an AST node that represents a block of statements. A block of statements is a sequence of statements that are executed together, such as those used in FuncDefStmt and IfStmt.

BlockStatement implements the Node interface.

func (*BlockStatement) String 

func (b *BlockStatement) String() string

String returns a string representation of the BlockStatement node.

func (*BlockStatement) Token 

func (b *BlockStatement) Token() *lexer.Token

Token returns the token of the Evy source program associated with the BlockStatement node.

func (*BlockStatement) Type 

func (b *BlockStatement) Type() *Type

Type returns NONE_TYPE for BlockStatement because a block statement does not have a type.

type BoolLiteral 

type BoolLiteral struct {
	Value bool
	// contains filtered or unexported fields
}

BoolLiteral is an AST node that represents a boolean literal. A boolean literal is a value that can be either true or false.

BoolLiteral implements the Node interface.

func (*BoolLiteral) String 

func (b *BoolLiteral) String() string

String returns a string representation of the BoolLiteral node.

func (*BoolLiteral) Token 

func (b *BoolLiteral) Token() *lexer.Token

Token returns the token of the Evy source program associated with the BoolLiteral node.

func (*BoolLiteral) Type 

func (b *BoolLiteral) Type() *Type

Type returns BOOL_TYPE for BoolLiteral as a bool literal always has the bool type.

type BreakStmt 

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

BreakStmt is an AST node that represents a break statement. A break statement is used to terminate the current loop statement, for example: 

while true
    break
end

BreakStmt implements the Node interface.

func (*BreakStmt) String 

func (*BreakStmt) String() string

String returns a string representation of the eakStmt node.

func (*BreakStmt) Token 

func (b *BreakStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the BreakStmt node.

func (*BreakStmt) Type 

func (*BreakStmt) Type() *Type

Type returns NONE_TYPE for BreakStmt because the empty statement does not have a type.

type Builtins 

type Builtins struct {
	Funcs         map[string]*FuncDefStmt
	EventHandlers map[string]*EventHandlerStmt
	Globals       map[string]*Var
}

Builtins holds all predefined, built-in function and event handler signatures, such as print and on animate. It also holds all global variables, such as err. The parsing process validates the Evy source code against the known built-ins.

type ConditionalBlock 

type ConditionalBlock struct {
	Condition Node // must be of type bool
	Block     *BlockStatement
	// contains filtered or unexported fields
}

ConditionalBlock is an AST node that represents a conditional block. A conditional block is a block of statements that is executed only if a certain condition is met. Conditional blocks are used in IfStmt and WhileStmt statements.

ConditionalBlock implements the Node interface.

func (*ConditionalBlock) String 

func (c *ConditionalBlock) String() string

String returns a string representation of the ConditionalBlock node.

func (*ConditionalBlock) Token 

func (c *ConditionalBlock) Token() *lexer.Token

Token returns the token of the Evy source program associated with the ConditionalBlock node.

func (*ConditionalBlock) Type 

func (c *ConditionalBlock) Type() *Type

Type returns NONE_TYPE for ConditionalBlock because a conditional block statement does not have a type.

type Decl 

type Decl struct {
	Var   *Var
	Value Node // literal, expression, variable, ...
	// contains filtered or unexported fields
}

Decl is an AST node that represents a variable declaration. A variable declaration is a statement that creates a new variable and assigns it a value. Variable declarations are used in TypedDeclStmt and InferredDeclStmt statements.

Decl implements the Node interface.

func (*Decl) String 

func (d *Decl) String() string

String returns a string representation of the Decl node.

func (*Decl) Token 

func (d *Decl) Token() *lexer.Token

Token returns the token of the Evy source program associated with the Decl node.

func (*Decl) Type 

func (d *Decl) Type() *Type

Type returns the type of the variable that is declared.

type DotExpression 

type DotExpression struct {
	T *Type

	Left Node
	Key  string // m := { age: 42}; m.age => key: "age"
	// contains filtered or unexported fields
}

DotExpression is an AST node that represents a field access expression. A field access expression is an expression that accesses the value of a field in a map, such as person.age.

DotExpression implements the Node interface.

func (*DotExpression) String 

func (d *DotExpression) String() string

String returns a string representation of the DotExpression node.

func (*DotExpression) Token 

func (d *DotExpression) Token() *lexer.Token

Token returns the token of the Evy source program associated with the DotExpression node.

func (*DotExpression) Type 

func (d *DotExpression) Type() *Type

Type returns the type of the DotExpression, which is the type of the map's values. For map := {a: true}, the type of map.a is bool.

type EmptyStmt 

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

EmptyStmt is an AST node that represents an empty statement. An empty statement is a statement that does nothing. Empty statement is used for formatting, such as to add a blank line between statements.

EmptyStmt implements the Node interface.

func (*EmptyStmt) String 

func (e *EmptyStmt) String() string

String returns a string representation of the EmptyStmt node.

func (*EmptyStmt) Token 

func (e *EmptyStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the EmptyStmt node.

func (*EmptyStmt) Type 

func (*EmptyStmt) Type() *Type

Type returns NONE_TYPE for EmptyStmt because the empty statement does not have a type.

type Error 

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

Error is an Evy parse error.

func (*Error) Error 

func (e *Error) Error() string

type Errors 

type Errors []*Error

Errors is a list of parse errors as we typically report more than a single parser error at a time to the end user. Errors itself also implements the error interfaced and can be treated like a single Error.

func (Errors) Error 

func (e Errors) Error() string

func (Errors) Truncate 

func (e Errors) Truncate(length int) Errors

Truncate truncates all parser errors from the length index onwards. This can make the result string of Errors.Error shorter if the combined error message is too long due to follow-on errors.

type EventHandlerStmt 

type EventHandlerStmt struct {
	Name   string
	Params []*Var
	Body   *BlockStatement
	// contains filtered or unexported fields
}

EventHandlerStmt is an AST node that represents an event handler definition. It includes the handler body, such as: 

on key k:string
    print "key pressed:" k
end

EventHandlerStmt implements the Node interface.

func (*EventHandlerStmt) String 

func (e *EventHandlerStmt) String() string

String returns a string representation of the EventHandlerStmt node.

func (*EventHandlerStmt) Token 

func (e *EventHandlerStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the EventHandlerStmt node.

func (*EventHandlerStmt) Type 

func (e *EventHandlerStmt) Type() *Type

Type returns NONE_TYPE for EventHandlerStmt because an event handler definition does not have a type.

type ForStmt 

type ForStmt struct {
	LoopVar *Var
	Range   Node // StepRange or array/map/string expression

	Block *BlockStatement
	// contains filtered or unexported fields
}

ForStmt is an AST node that represents a for loop. A for loop is a statement that repeats a block of code a certain number of times. The following code snippet is an example of a for loop: 

for n := range 1 10 2
    print n // 1 3 5 7 9
end

ForStmt implements the Node interface.

func (*ForStmt) String 

func (f *ForStmt) String() string

String returns a string representation of the ForStmt node.

func (*ForStmt) Token 

func (f *ForStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the ForStmt node.

func (*ForStmt) Type 

func (f *ForStmt) Type() *Type

Type returns NONE_TYPE for ForStmt because a while statement does not have a type.

type FuncCall 

type FuncCall struct {
	Name      string
	Arguments []Node
	FuncDef   *FuncDefStmt
	// contains filtered or unexported fields
}

FuncCall is an AST node that represents a function call. It can be used either as a standalone statement or as part of an expression.

FuncCall implements the Node interface.

func (*FuncCall) String 

func (f *FuncCall) String() string

String returns a string representation of the FuncCall node.

func (*FuncCall) Token 

func (f *FuncCall) Token() *lexer.Token

Token returns the token of the Evy source program associated with the FuncCall node.

func (*FuncCall) Type 

func (f *FuncCall) Type() *Type

Type returns the return type of the called function.

type FuncCallStmt 

type FuncCallStmt struct {
	FuncCall *FuncCall
	// contains filtered or unexported fields
}

FuncCallStmt is an AST node that represents a standalone function call statement. It is a statement that calls a function without any surrounding expressions.

FuncCallStmt implements the Node interface.

func (*FuncCallStmt) String 

func (f *FuncCallStmt) String() string

String returns a string representation of the FuncCallStmt node.

func (*FuncCallStmt) Token 

func (f *FuncCallStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the FuncCallStmt node.

func (*FuncCallStmt) Type 

func (f *FuncCallStmt) Type() *Type

Type returns the return type of the called function.

type FuncDefStmt 

type FuncDefStmt struct {
	Name              string
	Params            []*Var
	VariadicParam     *Var
	ReturnType        *Type
	VariadicParamType *Type
	Body              *BlockStatement
	// contains filtered or unexported fields
}

FuncDefStmt is an AST node that represents a function definition. It defines a new function with a name, a parameter list, return type, and a body. For example: 

func greet
    print "howdy!"
end

FuncDefStmt implements the Node interface.

func (*FuncDefStmt) String 

func (f *FuncDefStmt) String() string

String returns a string representation of the FuncDefStmt node.

func (*FuncDefStmt) Token 

func (f *FuncDefStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the FuncDefStmt node.

func (*FuncDefStmt) Type 

func (f *FuncDefStmt) Type() *Type

Type returns the return type of the function.

type GroupExpression 

type GroupExpression struct {
	Expr Node
	// contains filtered or unexported fields
}

GroupExpression is an AST node that represents a parenthesized expression. It groups together an expression so that it can be evaluated as a single unit, such as:(a+b)*3.

GroupExpression implements the Node interface.

func (*GroupExpression) String 

func (d *GroupExpression) String() string

String returns a string representation of the GroupExpression node.

func (*GroupExpression) Token 

func (d *GroupExpression) Token() *lexer.Token

Token returns the token of the Evy source program associated with the GroupExpression node.

func (*GroupExpression) Type 

func (d *GroupExpression) Type() *Type

Type returns the type of the GroupExpression, for example num for 2*(3+4).

type IfStmt 

type IfStmt struct {
	IfBlock      *ConditionalBlock
	ElseIfBlocks []*ConditionalBlock
	Else         *BlockStatement
	// contains filtered or unexported fields
}

IfStmt is an AST node that represents a conditional statement. It specifies a condition that must be met for a block of statements to be executed. It can optionally have else-if and else blocks. For example: 

if 2 * 5 == 10
    print "✔"
end

IfStmt implements the Node interface.

func (*IfStmt) String 

func (i *IfStmt) String() string

String returns a string representation of the IfStmt node.

func (*IfStmt) Token 

func (i *IfStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the IfStmt node.

func (*IfStmt) Type 

func (i *IfStmt) Type() *Type

Type returns NONE_TYPE for IfStmt because an if statement doest not have a type.

type IndexExpression 

type IndexExpression struct {
	T *Type

	Left  Node
	Index Node
	// contains filtered or unexported fields
}

IndexExpression is an AST node that represents an indexing expression. It accesses the value of an element in an array, map or string. For example: array[i].

IndexExpression implements the Node interface.

func (*IndexExpression) String 

func (i *IndexExpression) String() string

String returns a string representation of the IndexExpression node.

func (*IndexExpression) Token 

func (i *IndexExpression) Token() *lexer.Token

Token returns the token of the Evy source program associated with the IndexExpression node.

func (*IndexExpression) Type 

func (i *IndexExpression) Type() *Type

Type returns the type of the IndexExpression, for example num for an array of numbers with type []num.

type InferredDeclStmt 

type InferredDeclStmt struct {
	Decl *Decl
	// contains filtered or unexported fields
}

InferredDeclStmt is an AST node that represents an inferred declaration statement. It declares a variable with a type that is inferred from the value that is assigned to it. For example: n := 1.

InferredDeclStmt implements the Node interface.

func (*InferredDeclStmt) String 

func (d *InferredDeclStmt) String() string

String returns a string representation of the InferredDeclStmt node.

func (*InferredDeclStmt) Token 

func (d *InferredDeclStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the InferredDeclStmt node.

func (*InferredDeclStmt) Type 

func (d *InferredDeclStmt) Type() *Type

Type returns the type of the variable that is declared.

type MapLiteral 

type MapLiteral struct {
	Pairs map[string]Node
	Order []string // Track insertion order of keys for deterministic output.
	T     *Type
	// contains filtered or unexported fields
}

MapLiteral is an AST node that represents a map literal. A map literal is a collection of key-value pairs, such as {a: 1, b: 2}.

MapLiteral implements the Node interface.

func (*MapLiteral) String 

func (m *MapLiteral) String() string

String returns a string representation of the MapLiteral node.

func (*MapLiteral) Token 

func (m *MapLiteral) Token() *lexer.Token

Token returns the token of the Evy source program associated with the MapLiteral node.

func (*MapLiteral) Type 

func (m *MapLiteral) Type() *Type

Type returns the type of the map literal such as {}num for {a:1 b:2}.

type Node 

type Node interface {
	// Token returns the token of the Evy source program associated with the node.
	Token() *lexer.Token
	// String returns a string representation of the node.
	String() string
	// Type returns the Evy type of the node, such as num, []string, NONE.
	Type() *Type
}

Node represents a node in the AST.

type NumLiteral 

type NumLiteral struct {
	Value float64
	// contains filtered or unexported fields
}

NumLiteral is an AST node that represents a numeric literal. A numeric literal is a number, such as 12 or 34.567.

NumLiteral implements the Node interface.

func (*NumLiteral) String 

func (n *NumLiteral) String() string

String returns a string representation of the NumLiteral node.

func (*NumLiteral) Token 

func (n *NumLiteral) Token() *lexer.Token

Token returns the token of the Evy source program associated with the NumLiteral node.

func (*NumLiteral) Type 

func (n *NumLiteral) Type() *Type

Type returns NUM_TYPE for NumLiteral as a number literal always has the num type.

type Operator 

type Operator int

Operator represents the operators used in binary and unary expressions. For example, the OP_ASTERISK operator represents the multiplication operator (*). 

const (
	OP_ILLEGAL Operator = iota
	OP_PLUS
	OP_MINUS
	OP_SLASH
	OP_ASTERISK
	OP_PERCENT

	OP_OR
	OP_AND

	OP_EQ
	OP_NOT_EQ
	OP_LT
	OP_GT
	OP_LTEQ
	OP_GTEQ

	OP_INDEX
	OP_DOT
	OP_BANG
)

Operators are represented as constants and are used in BinaryExpression and UnaryExpression.

func (Operator) String 

func (o Operator) String() string

String returns a string representation of the operator, such as "+" for OP_PLUS.

type Program 

type Program struct {

	// Statements is the ordered list of top level block and basic statements of the given Evy program.
	Statements []Node
	// EventHandlers maps event names to their event handler statements.
	// It is used in web interface to set connect up relevant handlers with JS event handlers.
	EventHandlers map[string]*EventHandlerStmt
	// CalledBuiltinFuncs is a list of builtin functions that are called
	// in the program. It is used in web interface to hide or show
	// Canvas and input widgets, such as sliders or readline text field.
	CalledBuiltinFuncs []string
	// contains filtered or unexported fields
}

Program is the top-level or root AST node. It represents the entire Evy program.

Program implements the Node interface.

func Parse 

func Parse(input string, builtins Builtins) (*Program, error)

Parse takes an Evy program and predefined builtin declarations and returns program's AST.

func (*Program) Format 

func (p *Program) Format() string

Format returns a string of the formatted program with consistent indentation and vertical whitespace.

func (*Program) String 

func (p *Program) String() string

String returns a string representation of the Program node.

func (*Program) Token 

func (p *Program) Token() *lexer.Token

Token returns the token of the Evy source program associated with the Program node.

func (*Program) Type 

func (*Program) Type() *Type

Type returns NONE_TYPE for Program because a program does not have a type.

type ReturnStmt 

type ReturnStmt struct {
	Value Node // literal, expression, variable, ...
	T     *Type
	// contains filtered or unexported fields
}

ReturnStmt is an AST node that represents a return statement. A return statement terminates the execution of a function and can return a value. For example: 

func square:num n:num
    return n * n
end

ReturnStmt implements the Node interface.

func (*ReturnStmt) String 

func (r *ReturnStmt) String() string

String returns a string representation of the ReturnStmt node.

func (*ReturnStmt) Token 

func (r *ReturnStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the ReturnStmt node.

func (*ReturnStmt) Type 

func (r *ReturnStmt) Type() *Type

Type returns the type of the value returned by the return statement.

type SliceExpression 

type SliceExpression struct {
	T *Type

	Left  Node
	Start Node
	End   Node
	// contains filtered or unexported fields
}

SliceExpression is an AST node that represents a slice expression. A slice expression is used to access a subsequence of an array or string, such as: array[1:4].

SliceExpression implements the Node interface.

func (*SliceExpression) String 

func (s *SliceExpression) String() string

String returns a string representation of the SliceExpression node.

func (*SliceExpression) Token 

func (s *SliceExpression) Token() *lexer.Token

Token returns the token of the Evy source program associated with the SliceExpression node.

func (*SliceExpression) Type 

func (s *SliceExpression) Type() *Type

Type returns the type of the SliceExpression, which is the same type as the array that is sliced or string if a string is sliced.

type StepRange 

type StepRange struct {
	Start Node // num expression or nil
	Stop  Node // num expression
	Step  Node // num expression or nil
	// contains filtered or unexported fields
}

StepRange is an AST node that represents a step range in a for loop. A step range is used to iterate over a sequence of numbers, starting from the first number and ending with the last number, incrementing by the step size. For example: 

for n := range 1 10 2
    print n // 1 3 5 7 9
end

StepRange implements the Node interface.

func (*StepRange) GetStart added in v0.1.94 

func (s *StepRange) GetStart() Node

GetStart returns the start value of the step range, returning the default 0 if s.Start == nil.

func (*StepRange) GetStep added in v0.1.94 

func (s *StepRange) GetStep() Node

GetStep returns the step value of the step range, returning the default 1 if s.Step == nil.

func (*StepRange) GetStop added in v0.1.94 

func (s *StepRange) GetStop() Node

GetStop returns the stop value of the step range. This is always s.Stop as there is no default for this as there is for start and step, but we have this method for symmetry.

func (*StepRange) String 

func (s *StepRange) String() string

String returns a string representation of the StepRange node.

func (*StepRange) Token 

func (s *StepRange) Token() *lexer.Token

Token returns the token of the Evy source program associated with the StepRange node.

func (*StepRange) Type 

func (s *StepRange) Type() *Type

Type returns NUM_TYPE for StepRange as a step range always represents a set of number value.

type StringLiteral 

type StringLiteral struct {
	Value string
	// contains filtered or unexported fields
}

StringLiteral is an AST node that represents a string literal. A string literal is a sequence of characters enclosed in double quotes, such as "abc".

StringLiteral implements the Node interface.

func (*StringLiteral) String 

func (s *StringLiteral) String() string

String returns a string representation of the StringLiteral node.

func (*StringLiteral) Token 

func (s *StringLiteral) Token() *lexer.Token

Token returns the token of the Evy source program associated with the StringLiteral node.

func (*StringLiteral) Type 

func (s *StringLiteral) Type() *Type

Type returns STRING_TYPE for StringLiteral as a string literal always has the string type.

type Type 

type Type struct {
	Name TypeName // string, num, bool, composite types array, map
	Sub  *Type    // e.g.: `[]int` : Type{Name: "array", Sub: &Type{Name: "int"} }

	// Fixed is a flag relevant only to composite types: arrays and maps. It
	// determines if the composite type can be converted (or coerced) to a
	// different composite type.
	//
	// *  Fixed is false: The composite type is flexible. It can be coerced
	//    to other composite types (e.g., []num to []any) or directly to the
	//    dynamic `any` type. This applies to composite literals and nested
	//    composite literals.
	// *  Fixed is true: The composite type is strict. It cannot be directly
	//    coerced to other composite types, only to the dynamic `any` type.
	//    This applies to variables and expressions (like array
	//    concatenations and slices).
	Fixed bool
}

Type holds a full representation of any Evy variable or value. It can represent basic types, such as numbers and strings, as well as composite types, such as arrays and maps. It is also used to represent the dynamic ANY_TYPE. For AST nodes that have no type NONE_TYPE is used.

func (*Type) Equals added in v0.0.192 

func (t *Type) Equals(t2 *Type) bool

Equals returns if t and t2 and all their sub types are equal in Name.

func (*Type) String 

func (t *Type) String() string

String returns a string representation of the Type.

type TypeAssertion 

type TypeAssertion struct {
	T *Type

	Left Node
	// contains filtered or unexported fields
}

TypeAssertion is an AST node that represents a type assertion expression. A type assertion expression is used to enforce the specific type of an any value. For example: 

val:any
val = 1
print val.(num)+2 // 3

TypeAssertion implements the Node interface.

func (*TypeAssertion) String 

func (t *TypeAssertion) String() string

String returns a string representation of the TypeAssertion node.

func (*TypeAssertion) Token 

func (t *TypeAssertion) Token() *lexer.Token

Token returns the token of the Evy source program associated with the TypeAssertion node.

func (*TypeAssertion) Type 

func (t *TypeAssertion) Type() *Type

Type returns the type of the TypeAssertion, which is the type that is asserted.

type TypeName 

type TypeName int

TypeName represents the enumerable basic types (such as num, string, and bool), categories of composite types (such as array and map), the dynamic type (any), and the none type, which is used where no type is expected. TypeName is used in the Type struct which fully specifies all types, including composite types. 

const (
	NUM TypeName = iota
	STRING
	BOOL
	ANY
	ARRAY
	MAP
	NONE // for functions without return value, declaration statements, etc.
)

The enumerated basic types, categories of composite types, any and none are defined as constants.

func (TypeName) String 

func (t TypeName) String() string

type TypedDeclStmt 

type TypedDeclStmt struct {
	Decl *Decl
	// contains filtered or unexported fields
}

TypedDeclStmt is an AST node that represents a typed declaration statement. A typed declaration statement declares a variable of an explicitly specified type, such as n:num.

TypedDeclStmt implements the Node interface.

func (*TypedDeclStmt) String 

func (d *TypedDeclStmt) String() string

String returns a string representation of the TypedDeclStmt node.

func (*TypedDeclStmt) Token 

func (d *TypedDeclStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the TypedDeclStmt node.

func (*TypedDeclStmt) Type 

func (d *TypedDeclStmt) Type() *Type

Type returns the type of the variable that is declared.

type UnaryExpression 

type UnaryExpression struct {
	Op    Operator
	Right Node
	// contains filtered or unexported fields
}

UnaryExpression is an AST node that represents a unary expression, such as: -n.

UnaryExpression implements the Node interface.

func (*UnaryExpression) String 

func (u *UnaryExpression) String() string

String returns a string representation of the UnaryExpression node.

func (*UnaryExpression) Token 

func (u *UnaryExpression) Token() *lexer.Token

Token returns the token of the Evy source program associated with the UnaryExpression node.

func (*UnaryExpression) Type 

func (u *UnaryExpression) Type() *Type

Type returns the type of the UnaryExpression, such as bool or num.

type Var 

type Var struct {
	Name string
	T    *Type
	// contains filtered or unexported fields
}

Var is an AST node that represents a variable, its name and type but not its value.

Var implements the Node interface.

func (*Var) String 

func (v *Var) String() string

String returns a string representation of the Var node.

func (*Var) Token 

func (v *Var) Token() *lexer.Token

Token returns the token of the Evy source program associated with the Var node.

func (*Var) Type 

func (v *Var) Type() *Type

Type returns the type of the variable.

type WhileStmt 

type WhileStmt struct {
	ConditionalBlock
}

WhileStmt is an AST node that represents a while statement, such as 

while true
    print "🌞"
end

WhileStmt implements the Node interface.

func (*WhileStmt) String 

func (w *WhileStmt) String() string

String returns a string representation of the WhileStmt node.

func (*WhileStmt) Token 

func (w *WhileStmt) Token() *lexer.Token

Token returns the token of the Evy source program associated with the WhileStmt node.

func (*WhileStmt) Type 

func (w *WhileStmt) Type() *Type

Type returns NONE_TYPE for WhileStmt because a while statement does not have a type.

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