ginger/expr/expr.go

package expr

import (
	"fmt"
	"io"
	"strconv"
	"strings"

	"github.com/mediocregopher/ginger/lexer"
)

// TODO empty blocks
// TODO empty parenthesis

// Actual represents the actual expression in question, and has certain
// properties. It is wrapped by Expr which also holds onto contextual
// information, like the token to which Actual was originally parsed from
type Actual interface {
	// Equal should return true if the type and value of the other expression
	// are equal.
	Equal(Actual) bool
}

// Expr contains the actual expression as well as some contextual information
// wrapping it. Most interactions will be with this and not with the Actual
// directly.
type Expr struct {
	Actual Actual

	// Token is a nice-to-have, nothing will break if it's not there
	Token lexer.Token
}

////////////////////////////////////////////////////////////////////////////////

// Bool represents a true or false value
type Bool bool

// Equal implements the Actual method
func (b Bool) Equal(e Actual) bool {
	bb, ok := e.(Bool)
	if !ok {
		return false
	}
	return bb == b
}

////////////////////////////////////////////////////////////////////////////////

// Int represents an integer value
type Int int64

// Equal implements the Actual method
func (i Int) Equal(e Actual) bool {
	ii, ok := e.(Int)
	if !ok {
		return false
	}
	return ii == i
}

////////////////////////////////////////////////////////////////////////////////

// String represents a string value
type String string

// Equal implements the Actual method
func (s String) Equal(e Actual) bool {
	ss, ok := e.(String)
	if !ok {
		return false
	}
	return ss == s
}

////////////////////////////////////////////////////////////////////////////////

// Identifier represents a binding to some other value which has been given a
// name
type Identifier string

// Equal implements the Actual method
func (id Identifier) Equal(e Actual) bool {
	idid, ok := e.(Identifier)
	if !ok {
		return false
	}
	return idid == id
}

////////////////////////////////////////////////////////////////////////////////

// Tuple represents a fixed set of expressions which are interacted with as if
// they were a single value
type Tuple []Expr

func (tup Tuple) String() string {
	strs := make([]string, len(tup))
	for i := range tup {
		strs[i] = fmt.Sprint(tup[i].Actual)
	}
	return "(" + strings.Join(strs, ", ") + ")"
}

// Equal implements the Actual method
func (tup Tuple) Equal(e Actual) bool {
	tuptup, ok := e.(Tuple)
	if !ok || len(tuptup) != len(tup) {
		return false
	}
	for i := range tup {
		if !tup[i].Actual.Equal(tuptup[i].Actual) {
			return false
		}
	}
	return true
}

////////////////////////////////////////////////////////////////////////////////

// Pipe represents a set of expressions which operate on values and return new
// values. The inputs of one expression in the pipe is the output of the
// previous expression
type Pipe []Expr

func (p Pipe) String() string {
	strs := make([]string, len(p))
	for i := range p {
		strs[i] = fmt.Sprint(p[i].Actual)
	}
	return "(" + strings.Join(strs, "|") + ")"
}

// Equal implements the Actual method
func (p Pipe) Equal(e Actual) bool {
	pp, ok := e.(Pipe)
	if !ok || len(pp) != len(p) {
		return false
	}
	for i := range p {
		if !p[i].Actual.Equal(pp[i].Actual) {
			return false
		}
	}
	return true
}

////////////////////////////////////////////////////////////////////////////////

// Statement represents an actual action which will be taken. The input value is
// used as the input to the pipe, and the output of the pipe is the output of
// the statement
type Statement struct {
	in   Expr
	pipe Pipe
}

func (s Statement) String() string {
	return fmt.Sprintf("(%v > %s)", s.in.Actual, s.pipe.String())
}

// Equal implements the Actual method
func (s Statement) Equal(e Actual) bool {
	ss, ok := e.(Statement)
	return ok && s.in.Actual.Equal(ss.in.Actual) && s.pipe.Equal(ss.pipe)
}

////////////////////////////////////////////////////////////////////////////////

// Block represents a set of statements which share a scope, i.e. If one
// statement binds a variable the rest of the statements in the block can use
// that variable, including sub-blocks within this one.
type Block []Statement

func (b Block) String() string {
	strs := make([]string, len(b))
	for i := range b {
		strs[i] = b[i].String()
	}
	return fmt.Sprintf("{ %s }", strings.Join(strs, " "))
}

// Equal implements the Actual method
func (b Block) Equal(e Actual) bool {
	bb, ok := e.(Block)
	if !ok {
		return false
	}
	for i := range b {
		if !b[i].Equal(bb[i]) {
			return false
		}
	}
	return true
}

////////////////////////////////////////////////////////////////////////////////

type exprErr struct {
	reason string
	err    error
	tok    lexer.Token
	tokCtx string // e.g. "block starting at" or "open paren at"
}

func (e exprErr) Error() string {
	var msg string
	if e.err != nil {
		msg = e.err.Error()
	} else {
		msg = e.reason
	}
	if err := e.tok.Err(); err != nil {
		msg += " - token error: " + err.Error()
	} else if (e.tok != lexer.Token{}) {
		msg += " - "
		if e.tokCtx != "" {
			msg += e.tokCtx + ": "
		}
		msg = fmt.Sprintf("%s [line:%d col:%d]", msg, e.tok.Row, e.tok.Col)
	}
	return msg
}

////////////////////////////////////////////////////////////////////////////////

// toks[0] must be start
func sliceEnclosedToks(toks []lexer.Token, start, end lexer.Token) ([]lexer.Token, []lexer.Token, error) {
	c := 1
	ret := []lexer.Token{}
	first := toks[0]
	for i, tok := range toks[1:] {
		if tok.Err() != nil {
			return nil, nil, exprErr{
				reason: fmt.Sprintf("missing closing %v", end),
				tok:    tok,
			}
		}

		if tok.Equal(start) {
			c++
		} else if tok.Equal(end) {
			c--
		}
		if c == 0 {
			return ret, toks[2+i:], nil
		}
		ret = append(ret, tok)
	}

	return nil, nil, exprErr{
		reason: fmt.Sprintf("missing closing %v", end),
		tok:    first,
		tokCtx: "starting at",
	}
}

// Parse reads in all expressions it can from the given io.Reader and returns
// them
func Parse(r io.Reader) ([]Expr, error) {
	toks := readAllToks(r)
	var ret []Expr
	var expr Expr
	var err error
	for len(toks) > 0 {
		if toks[0].TokenType == lexer.EOF {
			return ret, nil
		}
		expr, toks, err = parse(toks)
		if err != nil {
			return nil, err
		}
		ret = append(ret, expr)
	}
	return ret, nil
}

// ParseAsBlock reads the given io.Reader as if it was implicitly surrounded by
// curly braces, making it into a Block. This means all expressions from the
// io.Reader *must* be statements. The returned Expr's Actual will always be a
// Block.
func ParseAsBlock(r io.Reader) (Expr, error) {
	return parseBlock(readAllToks(r))
}

func readAllToks(r io.Reader) []lexer.Token {
	l := lexer.New(r)
	var toks []lexer.Token
	for l.HasNext() {
		toks = append(toks, l.Next())
	}
	return toks
}

// For all parse methods it is assumed that toks is not empty

var (
	openParen  = lexer.Token{TokenType: lexer.Wrapper, Val: "("}
	closeParen = lexer.Token{TokenType: lexer.Wrapper, Val: ")"}
	openCurly  = lexer.Token{TokenType: lexer.Wrapper, Val: "{"}
	closeCurly = lexer.Token{TokenType: lexer.Wrapper, Val: "}"}
	comma      = lexer.Token{TokenType: lexer.Punctuation, Val: ","}
	pipe       = lexer.Token{TokenType: lexer.Punctuation, Val: "|"}
	arrow      = lexer.Token{TokenType: lexer.Punctuation, Val: ">"}
)

func parse(toks []lexer.Token) (Expr, []lexer.Token, error) {
	expr, toks, err := parseSingle(toks)
	if err != nil {
		return Expr{}, nil, err
	}

	if len(toks) > 0 && toks[0].TokenType == lexer.Punctuation {
		return parseConnectingPunct(toks, expr)
	}

	return expr, toks, nil
}

func parseSingle(toks []lexer.Token) (Expr, []lexer.Token, error) {
	var expr Expr
	var err error

	if toks[0].Err() != nil {
		return Expr{}, nil, exprErr{
			reason: "could not parse token",
			tok:    toks[0],
		}
	}

	if toks[0].Equal(openParen) {
		starter := toks[0]
		var ptoks []lexer.Token
		ptoks, toks, err = sliceEnclosedToks(toks, openParen, closeParen)
		if err != nil {
			return Expr{}, nil, err
		}

		if expr, ptoks, err = parse(ptoks); err != nil {
			return Expr{}, nil, err
		} else if len(ptoks) > 0 {
			return Expr{}, nil, exprErr{
				reason: "multiple expressions inside parenthesis",
				tok:    starter,
				tokCtx: "starting at",
			}
		}
		return expr, toks, nil

	} else if toks[0].Equal(openCurly) {
		var btoks []lexer.Token
		btoks, toks, err = sliceEnclosedToks(toks, openCurly, closeCurly)
		if err != nil {
			return Expr{}, nil, err
		}

		if expr, err = parseBlock(btoks); err != nil {
			return Expr{}, nil, err
		}
		return expr, toks, nil
	}

	if expr, err = parseNonPunct(toks[0]); err != nil {
		return Expr{}, nil, err
	}
	return expr, toks[1:], nil
}

func parseNonPunct(tok lexer.Token) (Expr, error) {
	if tok.TokenType == lexer.Identifier {
		return parseIdentifier(tok)
	} else if tok.TokenType == lexer.String {
		return parseString(tok)
	}

	return Expr{}, exprErr{
		reason: "unexpected non-punctuation token",
		tok:    tok,
	}
}

func parseIdentifier(t lexer.Token) (Expr, error) {
	e := Expr{Token: t}
	if t.Val[0] == '-' || (t.Val[0] >= '0' && t.Val[0] <= '9') {
		n, err := strconv.ParseInt(t.Val, 10, 64)
		if err != nil {
			return Expr{}, exprErr{
				err: err,
				tok: t,
			}
		}
		e.Actual = Int(n)

	} else if t.Val == "true" {
		e.Actual = Bool(true)

	} else if t.Val == "false" {
		e.Actual = Bool(false)

	} else {
		e.Actual = Identifier(t.Val)
	}

	return e, nil
}

func parseString(t lexer.Token) (Expr, error) {
	str, err := strconv.Unquote(t.Val)
	if err != nil {
		return Expr{}, exprErr{
			err: err,
			tok: t,
		}
	}
	return Expr{Token: t, Actual: String(str)}, nil
}

func parseConnectingPunct(toks []lexer.Token, root Expr) (Expr, []lexer.Token, error) {
	if toks[0].Equal(comma) {
		return parseTuple(toks, root)

	} else if toks[0].Equal(pipe) {
		return parsePipe(toks, root)

	} else if toks[0].Equal(arrow) {
		expr, toks, err := parse(toks[1:])
		if err != nil {
			return Expr{}, nil, err
		}
		pipe, ok := expr.Actual.(Pipe)
		if !ok {
			pipe = Pipe{expr}
		}
		return Expr{Token: root.Token, Actual: Statement{in: root, pipe: pipe}}, toks, nil
	}

	return root, toks, nil
}

func parseTuple(toks []lexer.Token, root Expr) (Expr, []lexer.Token, error) {
	rootTup, ok := root.Actual.(Tuple)
	if !ok {
		rootTup = Tuple{root}
	}

	// rootTup is modified throughout, be we need to make it into an Expr for
	// every return, which is annoying. so make a function to do it on the fly
	mkRoot := func() Expr {
		return Expr{Token: rootTup[0].Token, Actual: rootTup}
	}

	if len(toks) < 2 {
		return mkRoot(), toks, nil
	} else if !toks[0].Equal(comma) {
		if toks[0].TokenType == lexer.Punctuation {
			return parseConnectingPunct(toks, mkRoot())
		}
		return mkRoot(), toks, nil
	}

	var expr Expr
	var err error
	if expr, toks, err = parseSingle(toks[1:]); err != nil {
		return Expr{}, nil, err
	}

	rootTup = append(rootTup, expr)
	return parseTuple(toks, mkRoot())
}

func parsePipe(toks []lexer.Token, root Expr) (Expr, []lexer.Token, error) {
	rootPipe, ok := root.Actual.(Pipe)
	if !ok {
		rootPipe = Pipe{root}
	}

	// rootPipe is modified throughout, be we need to make it into an Expr for
	// every return, which is annoying. so make a function to do it on the fly
	mkRoot := func() Expr {
		return Expr{Token: rootPipe[0].Token, Actual: rootPipe}
	}

	if len(toks) < 2 {
		return mkRoot(), toks, nil
	} else if !toks[0].Equal(pipe) {
		if toks[0].TokenType == lexer.Punctuation {
			return parseConnectingPunct(toks, mkRoot())
		}
		return mkRoot(), toks, nil
	}

	var expr Expr
	var err error
	if expr, toks, err = parseSingle(toks[1:]); err != nil {
		return Expr{}, nil, err
	}

	rootPipe = append(rootPipe, expr)
	return parsePipe(toks, mkRoot())
}

// parseBlock assumes that the given token list is the entire block, already
// pulled from outer curly braces by sliceEnclosedToks, or determined to be the
// entire block in some other way.
func parseBlock(toks []lexer.Token) (Expr, error) {
	b := Block{}
	first := toks[0]
	var expr Expr
	var err error
	for {
		if len(toks) == 0 {
			return Expr{Token: first, Actual: b}, nil
		}

		if expr, toks, err = parse(toks); err != nil {
			return Expr{}, err
		}
		stmt, ok := expr.Actual.(Statement)
		if !ok {
			return Expr{}, exprErr{
				reason: "blocks may only contain full statements",
				tok:    expr.Token,
				tokCtx: "non-statement here",
			}
		}
		b = append(b, stmt)
	}
}