lexer/lexer.go

@@ -0,0 +1,54 @@
+// Package lexer provides basic helpers to implement parsers
+package lexer
+
+import "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 {
+	var err error
+
+	for fn != nil && err == nil {
+		fn, err = fn()
+	}
+
+	return 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 Accept(src io.RuneScanner, cond func(r rune) bool) bool {
+	r, _, err := src.ReadRune()
+	switch {
+	case err != nil:
+		return false
+	case cond(r):
+		return true
+	default:
+		_ = src.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 AcceptAll(src io.RuneScanner, cond func(r rune) bool) bool {
+	var accepted bool
+
+	for {
+		r, _, err := src.ReadRune()
+		switch {
+		case err != nil:
+			return accepted
+		case cond(r):
+			accepted = true
+		default:
+			_ = src.UnreadRune()
+			return accepted
+		}
+	}
+}

lexer/position.go

@@ -0,0 +1,68 @@
+package lexer
+
+import "fmt"
+
+// Position indicates a line and column pair on a file.
+// Counting starts at 1.
+type Position struct {
+	Line   int
+	Column int
+}
+
+// String generates a pretty "(Line, Column)"" representation of the Position
+func (p Position) String() string {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	return fmt.Sprintf("(%v, %v)", p.Line, p.Column)
+}
+
+// GoString generates a string representation of the Position for %#v usage
+func (p Position) GoString() string {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	return fmt.Sprintf("lexer.Position{%v, %v}", p.Line, p.Column)
+}
+
+// Reset places a position at (1,1)
+func (p *Position) Reset() {
+	p.Line, p.Column = 1, 1
+}
+
+// Step moves the column one place
+func (p *Position) Step() {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	p.Column++
+}
+
+// Next returns a new Position one rune forward
+// on the line
+func (p Position) Next() Position {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	return Position{
+		Line:   p.Line,
+		Column: p.Column + 1,
+	}
+}
+
+// NextLine returns a new Position at the begining of the next
+// line.
+func (p Position) NextLine() Position {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	return Position{
+		Line:   p.Line + 1,
+		Column: 1,
+	}
+}