133 lines
2.7 KiB
Go
133 lines
2.7 KiB
Go
package vm
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import (
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"context"
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"fmt"
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"regexp"
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"git.defalsify.org/festive/cache"
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"git.defalsify.org/festive/state"
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)
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var (
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inputRegexStr = "^[a-zA-Z0-9].*$"
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inputRegex = regexp.MustCompile(inputRegexStr)
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ctrlRegexStr = "^[><_^]$"
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ctrlRegex = regexp.MustCompile(ctrlRegexStr)
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symRegexStr = "^[a-zA-Z0-9][a-zA-Z0-9_]+$"
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symRegex = regexp.MustCompile(symRegexStr)
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)
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// CheckInput validates the given byte string as client input.
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func ValidInput(input []byte) error {
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if !inputRegex.Match(input) {
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return fmt.Errorf("Input '%s' does not match input format /%s/", input, inputRegexStr)
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}
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return nil
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}
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// control characters for relative navigation.
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func validControl(input []byte) error {
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if !ctrlRegex.Match(input) {
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return fmt.Errorf("Input '%s' does not match 'control' format /%s/", input, ctrlRegexStr)
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}
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return nil
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}
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// CheckSym validates the given byte string as a node symbol.
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func ValidSym(input []byte) error {
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if !symRegex.Match(input) {
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return fmt.Errorf("Input '%s' does not match 'sym' format /%s/", input, symRegexStr)
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}
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return nil
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}
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// false if target is not valid
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func valid(target []byte) bool {
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var ok bool
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if len(target) == 0 {
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return false
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}
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err := ValidSym(target)
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if err == nil {
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ok = true
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}
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if !ok {
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err = validControl(target)
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if err == nil {
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ok = true
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}
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}
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return ok
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}
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// CheckTarget tests whether the navigation state transition is available in the current state.
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//
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// Fails if target is formally invalid, or if navigation is unavailable.
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func CheckTarget(target []byte, st *state.State) (bool, error) {
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ok := valid(target)
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if !ok {
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return false, fmt.Errorf("invalid target: %x", target)
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}
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switch target[0] {
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case '_':
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topOk, err := st.Top()
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if err!= nil {
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return false, err
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}
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return topOk, nil
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case '<':
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_, prevOk := st.Sides()
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return prevOk, nil
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case '>':
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nextOk, _ := st.Sides()
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return nextOk, nil
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}
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return true, nil
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}
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// route parsed target symbol to navigation state change method,
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func applyTarget(target []byte, st *state.State, ca cache.Memory, ctx context.Context) (string, uint16, error) {
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var err error
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sym, idx := st.Where()
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ok := valid(target)
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if !ok {
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return sym, idx, fmt.Errorf("invalid input: %x", target)
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}
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switch target[0] {
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case '_':
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sym, err = st.Up()
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ca.Pop()
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if err != nil {
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return sym, idx, err
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}
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case '>':
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idx, err = st.Next()
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if err != nil {
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return sym, idx, err
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}
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case '<':
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idx, err = st.Previous()
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if err != nil {
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return sym, idx, err
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}
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case '^':
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_, err := st.SetFlag(state.FLAG_TERMINATE)
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if err != nil {
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return sym, idx, err
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}
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default:
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sym = string(target)
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st.Down(sym)
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ca.Push()
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idx = 0
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}
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return sym, idx, nil
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}
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