From d83b128c30087bed68d8c940c463d9994462eb38 Mon Sep 17 00:00:00 2001
From: Alejandro Mery <amery@jpi.io>
Date: Mon, 28 Aug 2023 22:35:30 +0000
Subject: [PATCH 1/2] lexer: introduce Reader.Accept()/AcceptAll()

Signed-off-by: Alejandro Mery <amery@jpi.io>
---
 lexer/reader.go | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/lexer/reader.go b/lexer/reader.go
index 7c0aaa3..6ab8c6b 100644
--- a/lexer/reader.go
+++ b/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 {

From 1d62857e14d89b4846d9dd8f15c9fae0e99467f0 Mon Sep 17 00:00:00 2001
From: Alejandro Mery <amery@jpi.io>
Date: Mon, 28 Aug 2023 22:14:45 +0000
Subject: [PATCH 2/2] lexer: introduce StateFn and the basic state machine loop

v2: make the error break more explicit

Signed-off-by: Alejandro Mery <amery@jpi.io>
---
 lexer/lexer.go | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/lexer/lexer.go b/lexer/lexer.go
index 33b17b6..e23ecad 100644
--- a/lexer/lexer.go
+++ b/lexer/lexer.go
@@ -1,2 +1,22 @@
 // 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 {
+	for fn != nil {
+		var err error
+
+		fn, err = fn()
+		if err != nil {
+			// failed
+			return err
+		}
+	}
+
+	// ended
+	return nil
+}