lexer: introduce StateFn and the basic state machine loop

Signed-off-by: Alejandro Mery <amery@jpi.io>

lexer/error.go

@@ -1,45 +0,0 @@
-package lexer
-
-import (
-	"fmt"
-	"strings"
-)
-
-var (
-	_ error = (*Error)(nil)
-)
-
-// Error represents a generic parsing error
-type Error struct {
-	Filename string
-	Line     int
-	Column   int
-
-	Content string
-	Err     error
-}
-
-func (err Error) Error() string {
-	var s []string
-
-	switch {
-	case err.Line > 0 || err.Column > 0:
-		s = append(s, fmt.Sprintf("%s:%v:%v", err.Filename, err.Line, err.Column))
-	case err.Filename != "":
-		s = append(s, err.Filename)
-	}
-
-	if err.Err != nil {
-		s = append(s, err.Err.Error())
-	}
-
-	if err.Content != "" {
-		s = append(s, fmt.Sprintf("%q", err.Content))
-	}
-
-	return strings.Join(s, ": ")
-}
-
-func (err Error) Unwrap() error {
-	return err.Err
-}

lexer/lexer.go

@@ -1,2 +1,17 @@
 // Package lexer provides basic helpers to implement parsers
 package lexer
+
+// StateFn is a State Function of the parser
+type StateFn func() (StateFn, error)
+
+// Run runs a state machine until the state function either
+// returns nil or an error
+func Run(fn StateFn) error {
+	var err error
+
+	for fn != nil && err == nil {
+		fn, err = fn()
+	}
+
+	return err
+}

lexer/reader.go

@@ -198,6 +198,41 @@ func (b *Reader) PeekRune() (rune, int, error) {
 	return r, l, err
 }
 
+// Accept consumes a rune from the source if it meets the condition.
+// it returns true if the condition was met and false if it wasn't.
+func (b *Reader) Accept(cond func(r rune) bool) bool {
+	r, _, err := b.ReadRune()
+	switch {
+	case err != nil:
+		return false
+	case cond(r):
+		return true
+	default:
+		_ = b.UnreadRune()
+		return false
+	}
+}
+
+// AcceptAll consumes runes from the source as long as they meet the
+// condition. it returns true if the condition was met for at least one rune,
+// and false if it wasn't.
+func (b *Reader) AcceptAll(cond func(r rune) bool) bool {
+	var accepted bool
+
+	for {
+		r, _, err := b.ReadRune()
+		switch {
+		case err != nil:
+			return accepted
+		case cond(r):
+			accepted = true
+		default:
+			_ = b.UnreadRune()
+			return accepted
+		}
+	}
+}
+
 // NewReader creates a new runes [Reader] using the given [io.Reader]
 func NewReader(r io.Reader) *Reader {
 	if r == nil {