diff --git a/lexer/lexer.go b/lexer/lexer.go new file mode 100644 index 0000000..39b0c8b --- /dev/null +++ b/lexer/lexer.go @@ -0,0 +1,83 @@ +// Package lexer provides basic helpers to implement parsers +package lexer + +import "io" + +// Lexer adds Accept and AcceptAll support to a +// [io.RuneScanner] +type Lexer struct { + io.RuneScanner +} + +// 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 (p Lexer) Accept(cond func(rune) bool) bool { + return Accept(p, cond) +} + +// 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 (p Lexer) AcceptAll(cond func(rune) bool) bool { + return AcceptAll(p, cond) +} + +// NewLexer extends a [io.RuneScanner] with Accept()/AcceptAll() +// functionality +func NewLexer(src io.RuneScanner) *Lexer { + if src == nil { + return nil + } + + return &Lexer{src} +} + +// 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 + } + } +} diff --git a/lexer/position.go b/lexer/position.go new file mode 100644 index 0000000..28db23c --- /dev/null +++ b/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, + } +}