package expr import ( "fmt" "io" "strconv" "github.com/mediocregopher/ginger/lexer" ) 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: ","} 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 if t.Val[0] == '%' { e.Actual = Macro(t.Val[1:]) } 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(arrow) { expr, toks, err := parse(toks[1:]) if err != nil { return Expr{}, nil, err } return Expr{Token: root.Token, Actual: Statement{In: root, To: expr}}, 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()) } // 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 } if _, ok := expr.Actual.(Statement); !ok { return Expr{}, exprErr{ reason: "blocks may only contain full statements", tok: expr.Token, tokCtx: "non-statement here", } } b = append(b, expr) } }