s-expression.go

// Package evaluator treats the element within expression with three types, each type has its own array form:
//
// - number
//     For convenience, we treat float64, int64 and so on as type of number. For example, float 100.0 is equal to int 100, but not euqal to string "100"
// - string
//    character string quoted with `, ', or " are treated as type of string. You can convert type string to any other defined type you like by type convert functions which are mentioned later
// - function or variable
//    character string without quotes are regarded as type of function or variable which depends on whether this function exists. For example in expression (age birthdate), both age and birthdate is unquoted. age is type of function because we have registered a function named age, while birthdate is type of variable for not found. The program will come to errors if there is neither parameter nor function named birthdate when evaluating
package evaluator

import (
	queue "container/list"
	"errors"
	"fmt"
	"reflect"
	"strconv"
	"unicode"
	"unicode/utf8"

	"github.com/nullne/evaluator/function"
)

var (
	// ErrUnexpectedEnd occurs most time with the missing parenthesis
	ErrUnexpectedEnd = errors.New("unexpected end")
	// ErrNilInput means the input is nil
	ErrNilInput = errors.New("nil input")
	// ErrLeftOverText indicates there are some of the expression are left pared
	ErrLeftOverText = errors.New("left over text")
	// ErrUnmatchedParenthesis indicated the mismatching parenthesis
	ErrUnmatchedParenthesis = errors.New("unmatched parenthesis")
)

// string without quoted is variable name
type varString string

func (q varString) String() string {
	return string(q)
}

// dynamic types for i are string, qString, float64, list
type sexp struct {
	// type of i must NOT be sexp
	i interface{}
}

func (exp sexp) evaluate(ps Params) (interface{}, error) {
	if l, isList := exp.i.(list); isList {
		if len(l) == 0 {
			return make([]interface{}, 0), nil
		}

		params := make([]interface{}, 0, len(l))
		for _, p := range l {
			v, err := p.evaluate(ps)
			if err != nil {
				return nil, err
			}
			params = append(params, v)
		}
		if fn, ok := params[0].(function.Func); ok {
			return fn(params[1:]...)
		}
		return params, nil
	}

	if val, ok := exp.i.(varString); ok {
		s := string(val)
		if fn, err := function.Get(s); err == nil {
			return fn, nil
		}
		return ps.Get(s)
	}
	return exp.i, nil
}

func (exp sexp) properties() []string {
	if l, isList := exp.i.(list); isList {
		if len(l) == 0 {
			return nil
		}
		var props []string
		for _, p := range l {
			props = append(props, p.properties()...)
		}
		return props
	}
	if val, ok := exp.i.(varString); ok {
		s := string(val)
		if _, err := function.Get(s); err == nil {
			return nil
		}
		return []string{s}
	}
	return nil
}

func parse(exp string) (sexp, error) {
	data := []byte(exp)
	tokens := queue.New()
ss:
	for i := 0; i < len(data); {
		advance, token, err := scan(data[i:])
		if err != nil {
			return sexp{}, err
		}
		i += advance
		if t, ok := token.(byte); ok && t == ')' {
			ins := queue.New()
			for e := tokens.Back(); e != nil; e = tokens.Back() {
				tokens.Remove(e)
				if v, ok := e.Value.(byte); ok && v == '(' {
					exps := make(list, 0, ins.Len())
					for e := ins.Back(); e != nil; e = e.Prev() {
						if p, ok := e.Value.(sexp); ok {
							exps = append(exps, p)
						} else {
							exps = append(exps, sexp{e.Value})
						}
					}
					tokens.PushBack(sexp{exps})
					continue ss
				}
				ins.PushBack(e.Value)
			}
			return sexp{}, ErrUnmatchedParenthesis
		}
		tokens.PushBack(token)
	}

	if tokens.Len() == 0 {
		return sexp{}, ErrNilInput
	} else if tokens.Len() != 1 {
		return sexp{}, ErrLeftOverText
	}
	if exp, ok := tokens.Back().Value.(sexp); ok {
		if l, ok := exp.i.(list); ok && len(l) == 0 {
			return sexp{}, ErrNilInput
		}
		return exp, nil
	}
	return sexp{tokens.Back().Value}, nil
}

func (exp sexp) String() string {
	return fmt.Sprintf("%v", exp.i)
}

func (exp sexp) dump(i int) {
	fmt.Printf("%*s%v: ", i*3, "", reflect.TypeOf(exp.i))
	if l, isList := exp.i.(list); isList {
		fmt.Printf("%d elements: %s\n", len(l), l)
		for _, e := range l {
			e.dump(i + 1)
		}
	} else {
		fmt.Println(exp)
	}
}

type list []sexp

func (l list) String() string {
	if len(l) == 0 {
		return "[]"
	}
	b := fmt.Sprintf("[%v", l[0])
	for _, s := range l[1:] {
		b = fmt.Sprintf("%s %v", b, s)
	}
	return b + "]"
}

func scan(data []byte) (advance int, token interface{}, err error) {
	length := len(data)
	start := 0
	for width := 0; start < length; start += width {
		var r rune
		r, width = utf8.DecodeRune(data[start:])
		if !unicode.IsSpace(r) {
			break
		}
	}
	if start >= length {
		return start, nil, nil
	}

	if b := data[start]; b == '\'' || b == '"' || b == '`' {
		advance, token, err = scanStringWithQuotesStriped(data[start:])
		return start + advance, string(token.([]byte)), err
	}

	for width, i := 0, start; i < length; i += width {
		if b := data[i]; b == ')' || b == '(' {
			if i == start {
				return start + 1, data[i], nil
			}
			return i, convert(data[start:i]), nil
		}
		var r rune
		r, width = utf8.DecodeRune(data[i:])
		if unicode.IsSpace(r) {
			return i, convert(data[start:i]), nil
		}
	}
	return len(data), convert(data[start:]), nil
}

func convert(data []byte) interface{} {
	// if v, err := strconv.ParseInt(string(data), 10, 0); err == nil {
	// 	return v
	// }
	if v, err := strconv.ParseFloat(string(data), 64); err == nil {
		return v
	}
	return varString(data)
}

// scanStringWithQuotesStriped scan string surrounded with ', " or something like this, a single character
func scanStringWithQuotesStriped(data []byte) (advance int, token []byte, err error) {
	length := len(data)
	if length == 0 {
		return 0, nil, nil
	}
	// escape character positions
	ecps := make([]int, 0, len(data))
	defer func() {
		// remove escape character
		if err != nil {
			return
		}
		tokenLen := len(token)
		tmp := make([]byte, 0, tokenLen)
		s := 0
		for _, p := range ecps {
			tmp = append(tmp, token[s:p]...)
			s = p + 1
		}
		if s < tokenLen {
			tmp = append(tmp, token[s:]...)
		}
		token = tmp
	}()

	delim := data[0]
	ecp := -1
	for i := 1; i < length; i++ {
		if data[i] == '\\' {
			ecp = i
		}
		if data[i] == delim {
			escapeEscaped := continuousCharacterCountFromBack(data[1:i], '\\')%2 == 0
			if ecp == i-1 && !escapeEscaped {
				ecps = append(ecps, ecp-1)
			} else {
				advance, token = i+1, data[1:i]
				return
			}
		}
	}
	return 0, nil, ErrUnexpectedEnd
}

func continuousCharacterCountFromBack(data []byte, key byte) int {
	length := len(data)
	for i := length; i > 0; i-- {
		if data[i-1] != key {
			return length - i
		}
	}
	return len(data)
}