First commit

core/parse/lexer.go

@@ -0,0 +1,122 @@
+package parse
+
+import (
+	"bufio"
+	"io"
+	"unicode"
+)
+
+type (
+	// lexer is a utility which can get values, token by
+	// token, from a Reader. A token is a word, and tokens
+	// are separated by whitespace. A word can be enclosed
+	// in quotes if it contains whitespace.
+	lexer struct {
+		reader *bufio.Reader
+		token  token
+		line   int
+	}
+
+	// token represents a single parsable unit.
+	token struct {
+		file string
+		line int
+		text string
+	}
+)
+
+// load prepares the lexer to scan an input for tokens.
+func (l *lexer) load(input io.Reader) error {
+	l.reader = bufio.NewReader(input)
+	l.line = 1
+	return nil
+}
+
+// next loads the next token into the lexer.
+// A token is delimited by whitespace, unless
+// the token starts with a quotes character (")
+// in which case the token goes until the closing
+// quotes (the enclosing quotes are not included).
+// Inside quoted strings, quotes may be escaped
+// with a preceding \ character. No other chars
+// may be escaped. The rest of the line is skipped
+// if a "#" character is read in. Returns true if
+// a token was loaded; false otherwise.
+func (l *lexer) next() bool {
+	var val []rune
+	var comment, quoted, escaped bool
+
+	makeToken := func() bool {
+		l.token.text = string(val)
+		return true
+	}
+
+	for {
+		ch, _, err := l.reader.ReadRune()
+		if err != nil {
+			if len(val) > 0 {
+				return makeToken()
+			}
+			if err == io.EOF {
+				return false
+			}
+			panic(err)
+		}
+
+		if quoted {
+			if !escaped {
+				if ch == '\\' {
+					escaped = true
+					continue
+				} else if ch == '"' {
+					quoted = false
+					return makeToken()
+				}
+			}
+			if ch == '\n' {
+				l.line++
+			}
+			if escaped {
+				// only escape quotes
+				if ch != '"' {
+					val = append(val, '\\')
+				}
+			}
+			val = append(val, ch)
+			escaped = false
+			continue
+		}
+
+		if unicode.IsSpace(ch) {
+			if ch == '\r' {
+				continue
+			}
+			if ch == '\n' {
+				l.line++
+				comment = false
+			}
+			if len(val) > 0 {
+				return makeToken()
+			}
+			continue
+		}
+
+		if ch == '#' {
+			comment = true
+		}
+
+		if comment {
+			continue
+		}
+
+		if len(val) == 0 {
+			l.token = token{line: l.line}
+			if ch == '"' {
+				quoted = true
+				continue
+			}
+		}
+
+		val = append(val, ch)
+	}
+}