Merge pull request 'lexer: constants and helpers' (#9)

Reviewed-on: #9

lexer/error.go

@@ -1,6 +1,7 @@
 package lexer
 
 import (
+	"errors"
 	"fmt"
 	"strings"
 )
@@ -9,6 +10,14 @@ var (
 	_ error = (*Error)(nil)
 )
 
+var (
+	// ErrUnacceptableRune indicates the read rune isn't acceptable in the context
+	ErrUnacceptableRune = errors.New("rune not acceptable in context")
+
+	// ErrNotImplemented indicates something hasn't been implemented yet
+	ErrNotImplemented = errors.New("not implemented")
+)
+
 // Error represents a generic parsing error
 type Error struct {
 	Filename string

lexer/lexer.go

@@ -1,2 +1,31 @@
 // Package lexer provides basic helpers to implement parsers
 package lexer
+
+import (
+	"errors"
+	"io"
+)
+
+// 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()
+		switch {
+		case errors.Is(err, io.EOF):
+			// EOF
+			return nil
+		case err != nil:
+			// failed
+			return err
+		}
+	}
+
+	// ended
+	return nil
+}

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 {

lexer/runes.go

@@ -0,0 +1,41 @@
+package lexer
+
+import (
+	"strings"
+	"unicode"
+)
+
+// NewIsNot generates a rune condition checker that reverses the
+// decision of the given checker.
+func NewIsNot(cond func(rune) bool) func(rune) bool {
+	return func(r rune) bool {
+		return !cond(r)
+	}
+}
+
+// NewIsIn generates a rune condition checker that accepts runes
+// contained on the provided string
+func NewIsIn(s string) func(rune) bool {
+	return func(r rune) bool {
+		return strings.ContainsRune(s, r)
+	}
+}
+
+// NewIsOneOf generates a run condition checker that accepts runes
+// accepted by any of the given checkers
+func NewIsOneOf(s ...func(rune) bool) func(rune) bool {
+	return func(r rune) bool {
+		for _, cond := range s {
+			if cond(r) {
+				return true
+			}
+		}
+		return false
+	}
+}
+
+// IsSpace reports whether the rune is a space character as
+// defined by Unicode's White Space property
+func IsSpace(r rune) bool {
+	return unicode.IsSpace(r)
+}