anglais/core/parser.go

package core

import (
	"errors"
	"fmt"
	"log"
	"math/big"
	"strconv"
	"strings"
)

type FormatedError interface {
	Error() string
	Format() string
}

type ParsingError struct {
	Description string
	Causer      *Token
	Source      string
	Trace       []string
}

func (p ParsingError) Error() string {
	return p.Description
}

// Format Print a rich and informative error
func (p ParsingError) Format() string {
	src := []rune(p.Source)
	b := strings.Builder{}

	lineNumber := 1
	lineBeginning := 0
	for i := 0; i < int(p.Causer.Start); i++ {
		if src[i] == '\n' {
			lineBeginning = i + 1
			lineNumber++
		}
	}

	lineEnd := len(src)
	for i := lineBeginning; i < len(src); i++ {
		if src[i] == '\n' {
			lineEnd = i
			break
		}
	}

	descriptor := fmt.Sprintf("%d:%d", lineNumber, int(p.Causer.Start)-lineBeginning+1)
	b.WriteString(p.Description)
	b.WriteRune('\n')

	b.WriteString(descriptor)
	b.WriteString(" | ")
	b.WriteString(string(src[lineBeginning:lineEnd]))

	b.WriteString("\n")
	b.WriteString(strings.Repeat(" ", len(descriptor)))
	b.WriteString("  ")
	for i := lineBeginning; i <= int(p.Causer.Start); i++ {
		b.WriteRune(' ')
	}

	for i := 0; i < len(p.Causer.Lexeme); i++ {
		b.WriteRune('^')
	}
	b.WriteRune('\n')
	b.WriteRune('\n')

	for i := len(p.Trace) - 1; i >= 0; i-- {
		b.WriteString(fmt.Sprintf("[%d] %s\n", i, p.Trace[i]))
	}

	return b.String()
}

type Parser struct {
	source string
	trace  []string
	tokens []Token
	state  ParserState
}

type ParserState struct {
	prev          *Token
	curr          *Token
	pos           Pos
	ignoreNewLine bool
}

func NewParser(source string, trace []string, tokens []Token) *Parser {
	return &Parser{
		source: source,
		trace:  trace,
		tokens: tokens,
		state: ParserState{
			pos: 0,
		},
	}
}

type Program struct {
	Block *BlockNode
	Path  string
}

func (p *Program) String() string {
	sb := strings.Builder{}

	sb.WriteString(fmt.Sprintf("=v= program %s =v=\n", p.Path))
	sb.WriteString(p.Block.String())
	sb.WriteString(fmt.Sprintf("=^= program %s =^=\n", p.Path))

	return sb.String()
}

func (p *Parser) Parse(path string) (*Program, error) {
	// top level statements
	statements := make([]Node, 0)

	// initialize current
	p.advance()

	for int(p.state.pos) < len(p.tokens) && p.state.curr.Kind != TokenEOF {
		for p.accept(TokenNewLine) {
		}

		if p.state.curr.Kind == TokenEOF {
			break
		}

		b, err := p.expression(false)

		if err != nil {
			return nil, err
		}

		if b != nil {
			statements = append(statements, b)
		}
	}

	return &Program{
		&BlockNode{
			statements,
			0,
			p.state.curr.End,
		},
		path,
	}, nil
}

func (p *Parser) accept(tokenType TokenKind) bool {
	if p.state.curr == nil {
		log.Fatal("unexpected current token nil")
		return false
	}

	if p.state.ignoreNewLine && tokenType != TokenNewLine {
		for p.state.curr.Kind == TokenNewLine {
			p.advance()
		}
	}

	if (*p.state.curr).Kind == tokenType {
		p.advance()
		return true
	}

	return false
}

func (p *Parser) getState() ParserState {
	return p.state
}

func (p *Parser) restoreState(state ParserState) {
	p.state = state
}

func (p *Parser) acceptSeq(tokenTypes ...TokenKind) bool {
	state := p.getState()

	for _, t := range tokenTypes {
		if !p.accept(t) {
			p.restoreState(state)
			return false
		}
	}

	return true
}

func (p *Parser) expect(tokenType TokenKind, reason string) error {
	if !p.accept(tokenType) {
		return p.error(fmt.Sprintf("Expected token %s, got %s; %s", tokenType, p.state.curr.Kind, reason), p.state.curr)
	}
	return nil
}

func (p *Parser) peek() (Token, error) {
	if p.state.pos >= Pos(len(p.tokens)) {
		return Token{}, errors.New("cannot peek beyond tokens")
	}

	return p.tokens[p.state.pos], nil
}

func (p *Parser) advance() {
	p.state.prev = p.state.curr

	if p.state.pos < Pos(len(p.tokens)) {
		p.state.curr = &p.tokens[p.state.pos]
	} else {
		p.state.curr = nil
	}

	p.state.pos++
}

func (p *Parser) error(error string, causer *Token) error {
	return ParsingError{
		Description: error,
		Causer:      causer,
		Source:      p.source,
		Trace:       p.trace,
	}
}

func (p *Parser) expression(mustBeBlock bool) (Node, error) {
	if mustBeBlock || p.accept(TokenOpenBrace) {
		if mustBeBlock {
			if err := p.expect(TokenOpenBrace, "expected block"); err != nil {
				return nil, err
			}
		}

		oldIgnoreNewline := p.state.ignoreNewLine
		p.state.ignoreNewLine = false

		start := p.state.prev.Start

		var statements []Node
		for !p.accept(TokenCloseBrace) {
			if p.accept(TokenNewLine) {
				continue
			}

			s, err := p.expression(false)
			if err != nil {
				return nil, err
			}

			statements = append(statements, s)

			if !p.accept(TokenNewLine) {
				if err := p.expect(TokenCloseBrace, "blocks must be closed"); err != nil {
					return nil, err
				}

				break
			}
		}

		p.state.ignoreNewLine = oldIgnoreNewline

		return &BlockNode{statements, start, p.state.prev.End}, nil
	}

	t := p.state.curr
	switch t.Kind {
	case TokenType:
		p.advance()
		start := p.state.prev.Start

		if err := p.expect(TokenName, "types must have a name"); err != nil {
			return nil, err
		}

		name := p.state.prev

		if err := p.expect(TokenAssign, "type aliases must be defined with an assign"); err != nil {
			return nil, err
		}

		sig, err := p.parseSignature()
		if err != nil {
			return nil, err
		}

		return &AliasNode{
			name,
			sig,

			start,
			p.state.prev.End,
		}, nil

	case TokenIf:
		p.advance()

		cond, err := p.expression(false)
		if err != nil {
			return nil, err
		}

		do, err := p.expression(true)
		if err != nil {
			return nil, err
		}

		var otherwise Node
		if p.accept(TokenElse) {
			otherwise, err = p.expression(p.state.curr.Kind != TokenIf)
			if err != nil {
				return nil, err
			}
		}

		return &ConditionalNode{
			cond,
			do,
			otherwise,
			t.Start,
			t.End,
		}, nil

	case TokenReturn:
		p.advance()
		start := p.state.prev.Start

		v, err := p.expression(false)
		if err != nil {
			return nil, err
		}

		return &ReturnNode{
			v,
			start,
			p.state.prev.End,
		}, nil

	case TokenWhile:
		p.advance()
		start := p.state.prev.Start

		cond, err := p.expression(false)
		if err != nil {
			return nil, err
		}

		logic, err := p.expression(true)
		if err != nil {
			return nil, err
		}

		return &LoopNode{
			cond,
			logic,
			start,
			p.state.prev.End,
		}, nil

	case TokenFor:
		p.advance()
		start := p.state.prev.Start

		counter, err := p.expression(false)
		if err != nil {
			return nil, err
		}

		if err := p.expect(TokenIn, "for-loops must be for each item in an iterator"); err != nil {
			return nil, err
		}

		iterator, err := p.expression(false)
		if err != nil {
			return nil, err
		}

		logic, err := p.expression(true)
		if err != nil {
			return nil, err
		}

		return &ForNode{
			counter,
			iterator,
			logic,

			start,
			p.state.prev.End,
		}, nil

	case TokenInclude:
		p.advance()
		start := p.state.prev.Start

		if err := p.expect(TokenString, "import requires a path/name to include"); err != nil {
			return nil, err
		}

		return &IncludeNode{
			&StringNode{
				p.state.prev.Lexeme[1 : len(p.state.prev.Lexeme)-1],
				p.state.prev.Lexeme,
				p.state.prev.Start,
				p.state.prev.End,
			},
			start,
			p.state.prev.End,
		}, nil

	default:
		s, err := p.binary()
		if err != nil {
			return nil, err
		}

		if p.accept(TokenDeclare) || p.accept(TokenAssign) {
			isDeclaration := p.state.prev.Kind == TokenDeclare

			// possibly assign tuples; not implemented yet
			v, err := p.expression(false)
			if err != nil {
				return nil, err
			}

			start, _ := s.Bounds()
			_, end := v.Bounds()

			return &AssignNode{
				s,
				v,
				isDeclaration,
				start,
				end,
			}, nil
		}

		return s, nil
	}
}

func isBinaryOperator(tokenType TokenKind) bool {
	switch tokenType {
	case TokenPlus, TokenMinus, TokenStar, TokenSlash, TokenPercent, TokenPipe, TokenDoubleAmpersand, TokenDoublePipe, TokenEquals, TokenBangEquals, TokenLessThan, TokenLessThanOrEqual, TokenGreaterThan, TokenGreaterThanOrEqual:
		return true
	default:
		return false
	}
}

func binaryPrecedence(op TokenKind) int {
	switch op {
	case TokenDoubleAmpersand, TokenDoublePipe:
		return 1
	case TokenEquals, TokenBangEquals, TokenLessThan, TokenGreaterThan, TokenLessThanOrEqual, TokenGreaterThanOrEqual:
		return 2
	case TokenPercent:
		return 3
	case TokenPlus, TokenMinus, TokenPipe:
		return 5
	case TokenStar, TokenSlash:
		return 10
	default:
		panic("unimplemented")
	}
}

func tokenToBinaryOperation(tokenType TokenKind) BinaryOperation {
	switch tokenType {
	case TokenPlus:
		return BinaryAddition
	case TokenMinus:
		return BinarySubtraction
	case TokenStar:
		return BinaryMultiplication
	case TokenSlash:
		return BinaryDivision
	case TokenPercent:
		return BinaryModulo
	case TokenPipe:
		panic("unimplemented bitwise ops")
	case TokenDoubleAmpersand:
		return BinaryBooleanAnd
	case TokenDoublePipe:
		return BinaryBooleanOr

	case TokenEquals:
		return BinaryEquality
	case TokenBangEquals:
		return BinaryInequality
	case TokenLessThan:
		return BinaryLess
	case TokenLessThanOrEqual:
		return BinaryLessEqual
	case TokenGreaterThan:
		return BinaryGreater
	case TokenGreaterThanOrEqual:
		return BinaryGreaterEqual

	default:
		panic("unimplemented")
	}
}

func (p *Parser) binary() (Node, error) {
	t, err := p.chain()
	if err != nil {
		return nil, err
	}

	ops := NewStack[*Token](128)
	values := NewStack[Node](256)
	values.pushItem(t)

	reduce := func() {
		r := values.Pop()
		l := values.Pop()
		opToken := ops.Pop()
		op := tokenToBinaryOperation(opToken.Kind)

		start, _ := l.Bounds()
		_, end := r.Bounds()

		values.Push(&BinaryNode{
			op,
			l,
			r,
			opToken,
			start,
			end,
		})
	}

	for isBinaryOperator(p.state.curr.Kind) {
		for ops.Current > 0 && binaryPrecedence(p.state.curr.Kind) <= binaryPrecedence(ops.Peek().Kind) {
			reduce()
		}

		ops.Push(p.state.curr)
		p.advance()

		v, err := p.chain()
		if err != nil {
			return nil, err
		}

		values.Push(v)
	}

	for ops.Current > 0 {
		reduce()
	}

	return values.Pop(), nil
}

func (p *Parser) chain() (Node, error) {
	f, err := p.factor()
	if err != nil {
		return nil, err
	}

	for {
		if p.accept(TokenDot) {
			if err = p.expect(TokenName, "can only access properties by name"); err != nil {
				return nil, err
			}
			name := p.state.prev

			f = &AccessNode{
				f,
				p.state.prev,
				name.Start,
				name.End,
			}

			if p.state.curr.Kind == TokenOpenParenthesis {
				args, err := p.parseArgs()
				if err != nil {
					return nil, err
				}

				f = &InvokeNode{
					f,
					args,
					name.Start,
					p.state.prev.End,
				}
			}
		} else if p.state.curr.Kind == TokenOpenParenthesis {
			start := p.state.curr.Start
			args, err := p.parseArgs()
			if err != nil {
				return nil, err
			}

			f = &InvokeNode{
				f,
				args,

				start,
				p.state.prev.End,
			}
		} else if p.accept(TokenOpenBracket) {
			start := p.state.prev.Start

			index, err := p.expression(false)
			if err != nil {
				return nil, err
			}

			if err := p.expect(TokenCloseBracket, "opening bracket must be closed"); err != nil {
				return nil, err
			}

			f = &IndexNode{
				f,
				index,
				start,
				p.state.prev.End,
			}
		} else {
			break
		}
	}

	return f, nil
}

func (p *Parser) factor() (Node, error) {
	switch (*p.state.curr).Kind {
	case TokenString:
		p.advance()
		return &StringNode{
			(*p.state.prev).Lexeme[1 : len((*p.state.prev).Lexeme)-1],
			(*p.state.prev).Lexeme,
			p.state.prev.Start,
			p.state.prev.End,
		}, nil

	case TokenInteger:
		p.advance()

		num, success := new(big.Int).SetString(p.state.prev.Lexeme, 10)
		if !success {
			return nil, p.error(fmt.Sprintf("cannot parse integer base 10: %s", p.state.prev.Lexeme), p.state.prev)
		}

		return &IntegerNode{
			num,
			p.state.prev.Start,
			p.state.prev.End,
		}, nil

	case TokenFloat:
		p.advance()
		num, err := strconv.ParseFloat((*p.state.prev).Lexeme, FloatSize)

		if err != nil {
			return nil, p.error(fmt.Sprintf("Error parsing number: %v", err), p.state.prev)
		}

		return &FloatNode{
			num,
			p.state.prev.Start,
			p.state.prev.End,
		}, nil

	case TokenHexadecimal:
		p.advance()
		start := (*p.state.prev).Start
		num, ok := new(big.Int).SetString(p.state.prev.Lexeme[2:], 16)
		if !ok {
			return nil, p.error(fmt.Sprintf("cannot parse hexadecimal: %v", p.state.prev.Lexeme), p.state.prev)
		}

		return &IntegerNode{
			num,
			start,
			p.state.prev.End,
		}, nil

	case TokenTrue:
		p.advance()
		return &BooleanNode{
			true,
			p.state.prev.Start,
			p.state.prev.End,
		}, nil
	case TokenFalse:
		p.advance()
		return &BooleanNode{
			false,
			p.state.prev.Start,
			p.state.prev.End,
		}, nil

	case TokenNil:
		p.advance()
		return &NilNode{}, nil

	case TokenOpenBracket:
		p.advance()
		start := p.state.prev.Start

		// TODO: find better solution; current one is messy
		// 		 Maybe perform better analysis to determine the kind of the list...
		if p.accept(TokenCloseBracket) {
			s, err := p.parseSignature()
			if err != nil {
				return nil, err
			}

			return &ListNode{
				[]Node{},
				s,
				start,
				p.state.prev.End,
			}, nil
		}

		oldIgnoreNewline := p.state.ignoreNewLine
		p.state.ignoreNewLine = true

		var values []Node
		for !p.accept(TokenCloseBracket) {
			if len(values) > 0 {
				if err := p.expect(TokenComma, "list values must be separated by a comma"); err != nil {
					return nil, err
				}
			}

			value, err := p.expression(false)
			if err != nil {
				return nil, err
			}

			values = append(values, value)
		}

		p.state.ignoreNewLine = oldIgnoreNewline

		return &ListNode{
			values,
			nil,
			start,
			p.state.prev.End,
		}, nil

	// unary minus
	case TokenMinus:
		p.advance()
		op := p.state.prev

		f, err := p.factor()
		if err != nil {
			return nil, err
		}
		return &UnaryNode{
			UnaryNegate,
			f,
			op,
			op.Start,
			p.state.prev.End,
		}, nil

	case TokenBang:
		p.advance()
		op := p.state.prev

		v, err := p.factor()
		if err != nil {
			return nil, err
		}

		return &UnaryNode{
			UnaryNot,
			v,
			op,
			op.Start,
			p.state.prev.End,
		}, nil

	case TokenName:
		p.advance()
		name := (*p.state.prev).Lexeme
		start := p.state.prev.Start
		nameEnd := p.state.prev.End

		if p.state.curr.Kind == TokenOpenParenthesis {
			args, err := p.parseArgs()
			if err != nil {
				return nil, err
			}

			return &InvokeNode{
				&ReferenceNode{
					name,
					start,
					nameEnd,
				},
				args,
				start,
				p.state.prev.End,
			}, nil
		}

		return &ReferenceNode{
			name,
			start,
			nameEnd,
		}, nil

	case TokenFunc:
		p.advance()
		start := p.state.prev.Start

		var name *Token
		if p.accept(TokenName) { // can be unnamed, but accept name if it is named
			name = p.state.prev
		}

		params, err := p.parseParams()
		if err != nil {
			return nil, err
		}

		var yield TypeSignature
		if p.accept(TokenArrow) {
			yield, err = p.parseSignature()
			if err != nil {
				return nil, err
			}
		}

		logic, err := p.expression(true)
		if err != nil {
			return nil, err
		}

		names := "*"
		if name != nil {
			names = name.Lexeme
		}

		fn := &FunctionNode{
			names,
			params,
			yield,
			logic,
			start,
			p.state.prev.End,
		}

		if name != nil {
			return &AssignNode{
				&ReferenceNode{name.Lexeme, name.Start, name.End},
				fn,
				true,
				start,
				p.state.prev.End,
			}, nil
		}

		return fn, nil

	case TokenOpenParenthesis:
		p.advance()
		start := p.state.prev.Start
		oldCare := p.state.ignoreNewLine
		p.state.ignoreNewLine = true
		p.skipNewLines()

		// we're inside an object
		key := p.state.curr
		if p.acceptSeq(TokenName, TokenColon) {
			entries := map[string]Node{}

			for len(entries) == 0 || !p.accept(TokenCloseParenthesis) {
				if len(entries) != 0 {
					p.skipNewLines()
					key = p.state.curr
					if !p.acceptSeq(TokenName, TokenColon) {
						return nil, p.error("expected a record name", key)
					}
				}

				name := key.Lexeme

				if _, ok := entries[name]; ok {
					return nil, p.error("duplicate key; already defined.", key)
				}

				if p.accept(TokenComma) || p.accept(TokenCloseParenthesis) {
					entries[name] = &ReferenceNode{
						name,
						key.Start,
						key.End,
					}

					if p.state.prev.Kind == TokenCloseParenthesis {
						break
					}

					continue
				} else {
					x, err := p.expression(false)
					if err != nil {
						return nil, err
					}

					entries[name] = x
				}

				if !p.accept(TokenComma) {
					if err := p.expect(TokenCloseParenthesis, "record must be closed"); err != nil {
						return nil, err
					}

					break
				}
			}

			p.state.ignoreNewLine = oldCare
			return &RecordNode{
				entries,
				start,
				p.state.prev.End,
			}, nil
		}

		v, err := p.expression(false)
		if err != nil {
			return nil, err
		}

		if !p.accept(TokenComma) {
			if err := p.expect(TokenCloseParenthesis, "parenthesis must be closed"); err != nil {
				return nil, err
			}

			p.state.ignoreNewLine = oldCare
			return v, nil
		}

		items := []Node{v}
		for !p.accept(TokenCloseParenthesis) {
			i, err := p.expression(false)
			if err != nil {
				return nil, err
			}

			items = append(items, i)

			if !p.accept(TokenComma) {
				if err := p.expect(TokenCloseParenthesis, "tuples must be closed"); err != nil {
					return nil, err
				}

				break
			}
		}

		p.state.ignoreNewLine = oldCare
		return &TupleNode{
			items,

			start,
			p.state.prev.End,
		}, nil

	case TokenBreakpoint:
		p.advance()

		return &BreakpointNode{
			p.state.prev.Start,
			p.state.prev.End,
		}, nil

	case TokenOpenBrace:
		return p.expression(true)

	default:
		return nil, p.error(fmt.Sprintf("invalid factor %s", p.state.curr), p.state.curr)
	}
}

func (p *Parser) parseArgs() ([]Node, error) {
	args := make([]Node, 0)

	if err := p.expect(TokenOpenParenthesis, "arguments must be contained in parenthesis"); err != nil {
		return nil, err
	}

	if !p.accept(TokenCloseParenthesis) {
		c, err := p.expression(false)
		if err != nil {
			return nil, err
		}
		args = append(args, c)
		for !p.accept(TokenCloseParenthesis) {
			if err := p.expect(TokenComma, "arguments must be separated by comma"); err != nil {
				return nil, err
			}
			c, err = p.expression(false)
			if err != nil {
				return nil, err
			}
			args = append(args, c)
		}
	}

	return args, nil
}

// parseParams parse parameters and parentheses
func (p *Parser) parseParams() ([]FunctionParameter, error) {
	if err := p.expect(TokenOpenParenthesis, "parameters must be in parentheses"); err != nil {
		return nil, err
	}
	params := make([]FunctionParameter, 0)

	if p.accept(TokenName) {
		name := (*p.state.prev).Lexeme
		if err := p.expect(TokenColon, "parameters must have a type separated by a colon"); err != nil {
			return nil, err
		}

		t, err := p.parseSignature()
		if err != nil {
			return nil, err
		}

		params = append(params, FunctionParameter{
			name,
			t,
		})
		for !p.accept(TokenCloseParenthesis) {
			if err := p.expect(TokenComma, "parameters must be separated by comma"); err != nil {
				return nil, err
			}
			if err := p.expect(TokenName, "parameters must have a name (cannot have trailing comma)"); err != nil {
				return nil, err
			}
			name = (*p.state.prev).Lexeme
			if err := p.expect(TokenColon, "parameters must have a type separated by a colon"); err != nil {
				return nil, err
			}

			t, err := p.parseSignature()
			if err != nil {
				return nil, err
			}

			params = append(params, FunctionParameter{
				name,
				t,
			})
		}
	} else {
		if err := p.expect(TokenCloseParenthesis, "must close parameter list"); err != nil {
			return nil, err
		}
	}

	return params, nil
}

func (p *Parser) parseSignature() (TypeSignature, error) {
	var s TypeSignature

	if p.accept(TokenOpenParenthesis) {
		oldCare := p.state.ignoreNewLine
		p.state.ignoreNewLine = true
		p.skipNewLines()

		// we're inside an object
		name := p.state.curr
		if p.acceptSeq(TokenName, TokenColon) {
			entries := map[string]TypeSignature{}

			for len(entries) == 0 || !p.accept(TokenCloseParenthesis) {
				if len(entries) != 0 {
					p.skipNewLines()
					name = p.state.curr
					if !p.acceptSeq(TokenName, TokenColon) {
						return nil, p.error("expected record member", p.state.curr)
					}
				}

				sig, err := p.parseSignature()
				if err != nil {
					return nil, err
				}

				entries[name.Lexeme] = sig

				if !p.accept(TokenComma) {
					if err := p.expect(TokenCloseParenthesis, "record must be closed"); err != nil {
						return nil, err
					}
					break
				}
			}

			return &RecordSignature{
				entries,
			}, nil
		}

		v, err := p.parseSignature()
		if err != nil {
			return nil, err
		}

		if !p.accept(TokenComma) {
			if err := p.expect(TokenCloseParenthesis, "parenthesis must be closed"); err != nil {
				return nil, err
			}

			s = v
		} else {
			items := []TypeSignature{v}
			for !p.accept(TokenCloseParenthesis) {
				i, err := p.parseSignature()
				if err != nil {
					return nil, err
				}

				items = append(items, i)

				if !p.accept(TokenComma) {
					if err := p.expect(TokenCloseParenthesis, "tuples must be closed"); err != nil {
						return nil, err
					}

					break
				}
			}
			s = &TupleSignature{
				items,
			}
		}

		p.state.ignoreNewLine = oldCare
	} else if p.accept(TokenFunc) {
		if err := p.expect(TokenOpenParenthesis, "func signature must have parentheses for parameters"); err != nil {
			return nil, err
		}

		var in []TypeSignature

		for !p.accept(TokenCloseParenthesis) {
			if len(in) > 0 {
				if err := p.expect(TokenComma, "parameter types must be separated by a comma"); err != nil {
					return nil, err
				}
			}

			sig, err := p.parseSignature()

			if err != nil {
				return nil, err
			}

			in = append(in, sig)
		}

		var out TypeSignature
		var err error
		if p.accept(TokenArrow) {
			out, err = p.parseSignature()
			if err != nil {
				return nil, err
			}
		} else {
			out = &NilSignature{}
		}

		s = &FunctionSignature{
			in,
			out,
		}
	} else if p.accept(TokenOpenBracket) {
		inner, err := p.parseSignature()
		if err != nil {
			return nil, err
		}
		if err := p.expect(TokenCloseBracket, "list type must be enclosed in brackets"); err != nil {
			return nil, err
		}

		return &ListSignature{inner}, nil
	} else {
		if err := p.expect(TokenName, "type must be a name"); err != nil {
			return nil, err
		}
		name := (*p.state.prev).Lexeme

		switch name {
		case "str":
			s = &StringSignature{}
		case "int":
			s = &IntegerSignature{}
		case "float":
			s = &FloatSignature{}
		case "bool":
			s = &BooleanSignature{}

		case "any":
			s = &AnySignature{}

		default:
			s = &NamedSignature{
				name,
			}
		}
	}

	if p.accept(TokenPipe) {
		other, err := p.parseSignature()
		if err != nil {
			return nil, err
		}
		return &CompositeSignature{
			s,
			other,
		}, nil
	}

	return s, nil
}

func (p *Parser) skipNewLines() {
	for p.accept(TokenNewLine) {
	}
}