Commit inicial

lex.go

@@ -0,0 +1,159 @@
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+type position struct {
+	pos          int
+	filepath     string
+	line, column int
+}
+
+func (p position) String() string {
+	return fmt.Sprintf("%s:%d:%d", p.filepath, p.line, p.column)
+}
+
+func (p *position) Position() position {
+	return *p
+}
+
+type Range [2]position
+
+type token[T comparable] struct {
+	position
+	value T
+}
+
+type Lexeme interface {
+	Position() position
+	Equals(Lexeme) bool
+}
+
+type Id string
+
+type Token token[string]
+
+type Int token[int]
+
+type Identifier token[Id]
+
+var (
+	Lparen      = &Token{value: "("}
+	Rparen      = &Token{value: ")"}
+	Space       = &Token{value: " "}
+	Tab         = &Token{value: "\t"}
+	Newline     = &Token{value: "\n"}
+	SingleQuote = &Token{value: "'"}
+	Let         = &Token{value: "let"}
+)
+
+func (t Token) String() string {
+	return fmt.Sprint(t.value)
+}
+
+func (t Int) String() string {
+	return fmt.Sprint(t.value)
+}
+
+func (t Identifier) String() string {
+	return fmt.Sprint(t.value)
+}
+
+var knownTokens = []*Token{
+	Lparen,
+	Rparen,
+	Space,
+	Tab,
+	Newline,
+	SingleQuote,
+	Let,
+}
+
+func (t *Token) Equals(a Lexeme) bool {
+	switch x := a.(type) {
+	case *Token:
+		return t.value == x.value
+	default:
+		return false
+	}
+}
+
+func (t *Int) Equals(a Lexeme) bool {
+	return false
+}
+
+func (t *Identifier) Equals(a Lexeme) bool {
+	switch x := a.(type) {
+	case *Identifier:
+		return t.value == x.value
+	default:
+		return false
+	}
+}
+
+var matchNumbers = regexp.MustCompile(`-?\d+`)
+var matchIdentifier = regexp.MustCompile(`[^\'() ]+`)
+
+func lex(source string) (*Input, error) {
+	var (
+		pos, line, column int
+		tokens            []Lexeme
+	)
+outer:
+	for len(source) > 0 {
+		p := position{pos: pos, line: line, column: column, filepath: "sourceinput"}
+		for _, try := range knownTokens {
+			if !strings.HasPrefix(source, try.value) {
+				continue
+			}
+			var (
+				l = len(try.value)
+				t = &Token{position: p, value: try.value}
+			)
+			source = source[l:]
+			pos += l
+			switch try {
+			case Newline:
+				line += 1
+				column = 0
+			case Tab, Space:
+				column += l
+			default:
+				column += l
+				tokens = append(tokens, t)
+			}
+			continue outer
+		}
+		index := matchNumbers.FindStringSubmatchIndex(source)
+		if index != nil && index[0] == 0 {
+			a := source[index[0]:index[1]]
+			conv, err := strconv.Atoi(a)
+			if err == nil {
+				var i = &Int{position: p, value: conv}
+				tokens = append(tokens, i)
+				l := len(a)
+				source = source[l:]
+				column += l
+				pos += l
+				continue outer
+			}
+		}
+		index = matchIdentifier.FindStringIndex(source)
+		if index != nil && index[0] == 0 {
+			a := source[index[0]:index[1]]
+			var id = &Identifier{position: p, value: Id(a)}
+			tokens = append(tokens, id)
+			l := len(a)
+			source = source[l:]
+			column += l
+			pos += l
+			continue outer
+		}
+		return nil, fmt.Errorf("unrecognized token '%c' at %s", source[0], p)
+	}
+	return &Input{input: tokens}, nil
+}