asciigoat's core library https://asciigoat.org/core
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// 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
}
}
}