scratch @ 2b64f4e6f2d35ae68bf39cec616a782153335bc0

package main

import (

	"errors"

	"fmt"

	"strconv"

	"strings"

	"unicode"

)

type TokenType int

const (

	TokenInvalid TokenType = iota

	TokenSym

	TokenNum

	TokenStr

	TokenOParen

	TokenCParen

	TokenComma

)

var TokenTypeName = map[TokenType]string{

	TokenInvalid: "TokenInvalid",

	TokenSym:     "TokenSym",

	TokenNum:     "TokenNum",

	TokenStr:     "TokenStr",

	TokenOParen:  "TokenOParen",

	TokenCParen:  "TokenCParen",

	TokenComma:   "TokenComma",

}

type Token struct {

	Type TokenType

	Text []rune

	Loc  Loc

}

type Loc struct {

	Filepath string

	Row, Col int

}

func (l Loc) String() string { return fmt.Sprintf("%s:%d:%d", l.Filepath, l.Row, l.Col) }

type DiagError struct {

	Loc Loc

	Err error

}

func (e *DiagError) Unwrap() error { return e.Err }

func (e *DiagError) Error() string {

	return fmt.Sprintf("%s: ERROR: %s", e.Loc, e.Err)

}

var (

	ErrLexerEOF           = errors.New("Lexer: End of file")

	ErrLexerUnclosedStr   = errors.New("Lexer: Unclosed String")

	ErrLexerInvalidEscape = errors.New("Lexer: Invalid Escape Sequence")

	ErrLexerInvalidToken  = errors.New("Lexer: Invalid Token")

)

type Lexer struct {

	Filepath string

	Content  []rune // TODO: bytes

	Row      int

	Cur      int

	Bol      int

	PeekTok  Token

	PeekErr  error

	PeekFull bool

}

func NewLexer(content []rune, filePath string) Lexer {

	return Lexer{

		Filepath: filePath,

		Content:  content,

	}

}

func (l *Lexer) ChopChar() {

	if l.Cur < len(l.Content) {

		x := l.Content[l.Cur]

		l.Cur += 1

		if x == '\n' {

			l.Bol = l.Cur

			l.Row += 1

		}

	}

}

func (l *Lexer) TrimLeft() {

	for l.Cur < len(l.Content) && unicode.IsSpace(l.Content[l.Cur]) {

		l.ChopChar()

	}

}

func (l Lexer) StartsWith(prefix []rune) bool {

	if l.Cur+len(prefix) > len(l.Content) {

		return false

	}

	for i := range prefix {

		if prefix[i] != l.Content[l.Cur+i] {

			return false

		}

	}

	return true

}

func (l *Lexer) Loc() Loc {

	return Loc{

		Filepath: l.Filepath,

		Row:      l.Row + 1,

		Col:      l.Cur - l.Bol + 1,

	}

}

func (l *Lexer) ChopWhile(p func(rune) bool) (result []rune) {

	for l.Cur < len(l.Content) && p(l.Content[l.Cur]) {

		result = append(result, l.Content[l.Cur])

		l.ChopChar()

	}

	return

}

func (l *Lexer) ChopToken() (Token, error) {

	t := Token{}

	l.TrimLeft()

	for l.Cur < len(l.Content) && l.StartsWith([]rune("--")) {

		for l.Cur < len(l.Content) && l.Content[l.Cur] != '\n' {

			l.ChopChar()

		}

		l.TrimLeft()

	}

	t.Loc = l.Loc()

	if l.Cur >= len(l.Content) {

		return t, ErrLexerEOF

	}

	first := l.Content[l.Cur]

	ps := []rune("(),")

	ts := []TokenType{TokenOParen, TokenCParen, TokenComma}

	for i := range ps {

		if first == ps[i] {

			t.Type = ts[i]

			t.Text = []rune{ps[i]}

			l.ChopChar()

			return t, nil

		}

	}

	if unicode.IsDigit(first) {

		t.Type = TokenNum

		t.Text = l.ChopWhile(unicode.IsDigit)

		return t, nil

	}

	if unicode.IsLetter(first) || first == '_' {

		t.Type = TokenSym

		t.Text = l.ChopWhile(func(x rune) bool {

			return unicode.IsLetter(x) || unicode.IsDigit(x) || x == '_'

		})

		return t, nil

	}

	if first == '"' {

		l.ChopChar()

		t.Type = TokenStr

		for l.Cur < len(l.Content) && l.Content[l.Cur] != '"' {

			if l.Content[l.Cur] == '\\' {

				l.ChopChar()

				if l.Cur >= len(l.Content) {

					return t, &DiagError{

						Loc: l.Loc(),

						Err: ErrLexerUnclosedStr,

					}

				}

				if l.Content[l.Cur] == '"' {

					t.Text = append(t.Text, '"')

					l.ChopChar()

				} else {

					loc := l.Loc()

					l.ChopChar()

					return t, &DiagError{

						Loc: loc,

						Err: fmt.Errorf("%w: %c", ErrLexerInvalidEscape, l.Content[l.Cur]),

					}

				}

			} else {

				t.Text = append(t.Text, l.Content[l.Cur])

				l.ChopChar()

			}

		}

		if l.Cur >= len(l.Content) {

			return t, &DiagError{

				Loc: l.Loc(),

				Err: ErrLexerUnclosedStr,

			}

		}

		l.ChopChar()

		return t, nil

	}

	l.ChopChar()

	return t, &DiagError{

		Loc: l.Loc(),

		Err: fmt.Errorf("%w: %c", ErrLexerInvalidToken, first),

	}

}

func (l *Lexer) Peek() (Token, error) {

	if !l.PeekFull {

		l.PeekTok, l.PeekErr = l.ChopToken()

		l.PeekFull = true

	}

	return l.PeekTok, l.PeekErr

}

func (l *Lexer) Next() (Token, error) {

	if l.PeekFull {

		l.PeekFull = false

	} else {

		l.PeekTok, l.PeekErr = l.ChopToken()

	}

	return l.PeekTok, l.PeekErr

}

type ExprType int

const (

	ExprVoid ExprType = iota

	ExprInt

	ExprStr

	ExprVar

	ExprFuncall

)

type Expr struct {

	Type ExprType

	Loc  Loc

	AsInt     int

	AsStr     string

	AsVar     string

	AsFuncall Funcall

}

type Funcall struct {

	Name string

	Args []Expr

}

func (funcall *Funcall) String() string {

	var result strings.Builder

	fmt.Fprintf(&result, "%s(", funcall.Name)

	for i, arg := range funcall.Args {

		if i > 0 {

			fmt.Fprintf(&result, ", ")

		}

		fmt.Fprintf(&result, "%s", arg.String())

	}

	fmt.Fprintf(&result, ")")

	return result.String()

}

func (expr *Expr) Dump(level int) {

	for i := 0; i < level; i += 1 {

		fmt.Printf("  ")

	}

	switch expr.Type {

	case ExprVoid:

		fmt.Printf("Void\n")

	case ExprInt:

		fmt.Printf("Int: %d\n", expr.AsInt)

	case ExprStr:

		fmt.Printf("Str: \"%s\"\n", expr.AsStr) // TODO: escape strings

	case ExprVar:

		fmt.Printf("Var: %s\n", expr.AsVar)

	case ExprFuncall:

		fmt.Printf("Funcall: %s\n", expr.AsFuncall.Name)

		for _, arg := range expr.AsFuncall.Args {

			arg.Dump(level + 1)

		}

	}

}

func (expr *Expr) String() string {

	switch expr.Type {

	case ExprVoid:

		return ""

	case ExprInt:

		return fmt.Sprintf("%d", expr.AsInt)

	case ExprStr:

		return fmt.Sprintf("\"%s\"", expr.AsStr) // TODO: escape string

	case ExprVar:

		return expr.AsVar

	case ExprFuncall:

		return expr.AsFuncall.String()

	default:

		panic("unreachable")

	}

}

var (

	ErrParserUnexpectedToken = errors.New("parser: Unexpected Token")

	ErrParserUnclosedFuncall = errors.New("parser: Unclosed Funcall")

)

func ParseExpr(l *Lexer) (Expr, error) {

	t, err := l.Next()

	if err != nil {

		return Expr{}, err

	}

	switch t.Type {

	case TokenSym:

		oparen, err := l.Peek()

		if err != nil || oparen.Type != TokenOParen {

			return Expr{

				Type:  ExprVar,

				Loc:   t.Loc,

				AsVar: string(t.Text),

			}, nil

		} else {

			l.Next()

			cparen, err := l.Peek()

			if err == nil && cparen.Type == TokenCParen {

				l.Next()

				return Expr{

					Type:      ExprFuncall,

					Loc:       t.Loc,

					AsFuncall: Funcall{Name: string(t.Text)},

				}, nil

			}

			arg, err := ParseExpr(l)

			if err != nil {

				return Expr{}, err

			}

			args := []Expr{arg}

			comma, err := l.Next()

			for err == nil && comma.Type == TokenComma {

				arg, err = ParseExpr(l)

				if err != nil {

					return Expr{}, err

				}

				args = append(args, arg)

				comma, err = l.Next()

			}

			if err == ErrLexerEOF || comma.Type != TokenCParen {

				return Expr{}, &DiagError{Loc: comma.Loc, Err: ErrParserUnclosedFuncall}

			}

			return Expr{

				Type: ExprFuncall,

				Loc:  t.Loc,

				AsFuncall: Funcall{

					Name: string(t.Text),

					Args: args,

				},

			}, nil

		}

	case TokenNum:

		s := string(t.Text)

		x, err := strconv.Atoi(s)

		if err != nil {

			return Expr{}, &DiagError{Loc: t.Loc, Err: err}

		}

		return Expr{

			Type:  ExprInt,

			Loc:   t.Loc,

			AsInt: x,

		}, nil

	case TokenStr:

		return Expr{

			Type:  ExprStr,

			Loc:   t.Loc,

			AsStr: string(t.Text),

		}, nil

	}

	return Expr{}, &DiagError{

		Loc: t.Loc,

		Err: fmt.Errorf("%w: %s", ErrParserUnexpectedToken, TokenTypeName[t.Type]),

	}

}

func ParseExprs(l *Lexer) ([]Expr, error) {

	exprs := []Expr{}

	for {

		expr, err := ParseExpr(l)

		if err != nil {

			if errors.Is(err, ErrLexerEOF) {

				err = nil

			}

			return exprs, err

		}

		exprs = append(exprs, expr)

	}

}

type (

	Func func(context *EvalContext, args []Expr) (Expr, error)

	EvalContext struct{ Scopes []EvalScope }

	EvalScope   struct {

		Vars  map[string]Expr

		Funcs map[string]Func

	}

)

func (e EvalContext) LookupVar(name string) (Expr, bool) {

	scopes := e.Scopes

	for len(scopes) > 0 {

		n := len(scopes)

		varr, ok := scopes[n-1].Vars[name]

		if ok {

			return varr, true

		}

		scopes = scopes[:n-1]

	}

	return Expr{}, false

}

func (e EvalContext) LookupFunc(name string) (Func, bool) {

	scopes := e.Scopes

	for len(scopes) > 0 {

		n := len(scopes)

		fun, ok := scopes[n-1].Funcs[name]

		if ok {

			return fun, true

		}

		scopes = scopes[:n-1]

	}

	return nil, false

}

func (e *EvalContext) PushScope(scope EvalScope) { e.Scopes = append(e.Scopes, scope) }

func (e *EvalContext) PopScope()                 { e.Scopes = e.Scopes[0 : len(e.Scopes)-1] }

func (e *EvalContext) TopScope() *EvalScope {

	length := len(e.Scopes)

	if length <= 0 {

		panic("No scopes found")

	}

	return &e.Scopes[length-1]

}

var (

	ErrRuntimeUnknownVar = errors.New("unknown runtime variable")

	ErrRuntimeUnknownFun = errors.New("unknown runtime function")

)

func (e *EvalContext) EvalExpr(expr Expr) (Expr, error) {

	switch expr.Type {

	case ExprVoid, ExprInt, ExprStr:

		return expr, nil

	case ExprVar:

		v, ok := e.LookupVar(expr.AsVar)

		if !ok {

			return Expr{}, fmt.Errorf("%s: ERROR: %w: %s", expr.Loc, ErrRuntimeUnknownVar, expr.AsVar)

		}

		return e.EvalExpr(v)

	case ExprFuncall:

		fn, ok := e.LookupFunc(expr.AsFuncall.Name)

		if !ok {

			return Expr{}, fmt.Errorf("%s: ERROR: %w: %s", expr.Loc, ErrRuntimeUnknownFun, expr.AsFuncall.Name)

		}

		return fn(e, expr.AsFuncall.Args)

	default:

		panic("unreachable")

	}

}