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Back out the error passing, in practive it did not work out well, bet…
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…ter for the user to handle it.
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Marek Dolgos committed Jan 13, 2016
1 parent c52a6e9 commit c4f5c67
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Showing 2 changed files with 48 additions and 128 deletions.
110 changes: 37 additions & 73 deletions dfa.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -5,19 +5,6 @@ import (
"fmt"
)

type Errors []error

func (e Errors) Error() string {
var buf bytes.Buffer
for i, err := range e {
buf.WriteString(err.Error())
if i < len(e)-1 {
buf.WriteString(", ")
}
}
return buf.String()
}

type State string

func (s State) String() string {
Expand All @@ -31,16 +18,15 @@ func (l Letter) String() string {
}

type DFA struct {
q map[State]bool // States
e map[Letter]bool // Alphabet
d map[domainelement]*codomainelement // Transition
q0 State // Start State
f map[State]bool // Terminal States
synccall bool // Call callbacks synchronously
done chan laststate // Termination channel
input *Letter // Inputs to the DFA
stop chan struct{}
logger func(State) // Logger for transitions
q map[State]bool // States
e map[Letter]bool // Alphabet
d map[domainelement]*codomainelement // Transition
q0 State // Start State
f map[State]bool // Terminal States
done chan laststate // Termination channel
input *Letter // Inputs to the DFA
stop chan struct{} // Stops the DFA
logger func(State) // Logger for transitions
}

type domainelement struct {
Expand All @@ -54,8 +40,8 @@ type codomainelement struct {
}

type laststate struct {
s State
errors Errors
s State
accepted bool
}

func New() *DFA {
Expand All @@ -80,16 +66,16 @@ func (m *DFA) SetTransition(from State, input Letter, to State, exec interface{}
panic("state cannot be defined as the empty string")
}
switch exec.(type) {
case func() error:
case func():
if !m.f[to] {
panic(fmt.Sprintf("stateful computation must be of type 'func() (Letter, error)' for non-terminal '%v' state", to))
panic(fmt.Sprintf("stateful computation must be of type 'func() Letter' for non-terminal '%v' state", to))
}
case func() (Letter, error):
case func() Letter:
if m.f[to] {
panic(fmt.Sprintf("stateful computation must be of type 'func() error' for terminal '%v' state", to))
panic(fmt.Sprintf("stateful computation must be of type 'func()' for terminal '%v' state", to))
}
default:
panic("stateful computation must be of type 'func() error' or 'func() (Letter, error)")
panic("stateful computation must be of type 'func()' or 'func() Letter")
}
m.q[to] = true
m.q[from] = true
Expand Down Expand Up @@ -136,8 +122,8 @@ func (m *DFA) Alphabet() []Letter {
}

// Run the DFA, blocking until Stop is called or the DFA enters a terminal state.
// Returns the terminal state and any errors.
func (m *DFA) Run(init interface{}) (State, error) {
// Returns the last state and true is the last state was a terminal state.
func (m *DFA) Run(init interface{}) (State, bool) {
// Check some pre-conditions.
if init == nil {
panic("initial stateful computation is nil")
Expand All @@ -159,32 +145,25 @@ func (m *DFA) Run(init interface{}) (State, error) {
// Run the DFA.
go func() {
defer close(m.done)
var errors Errors
// The current state, starts at q0.
s := m.q0
// Run the initial stateful computation.
if m.f[s] {
// If the state is a terminal state then the DFA has
// accepted the input sequence and it can stop.
m.done <- laststate{s, errors}
m.done <- laststate{s, true}
return
} else {
// Otherwise continue reading generated input
// by starting the next stateful computation.
switch init := init.(type) {
case func() error:
case func():
m.logger(s)
if err := init(); err != nil {
errors = append(errors, err)
}
case func() (Letter, error):
init()
case func() Letter:
m.logger(s)
if l, err := init(); err != nil {
errors = append(errors, err)
m.input = &l
} else {
m.input = &l
}
l := init()
m.input = &l
}
}
for {
Expand All @@ -201,9 +180,7 @@ func (m *DFA) Run(init interface{}) (State, error) {
l := *m.input
// Reject upfront if letter is not in alphabet.
if !m.e[l] {
errors = append(errors, fmt.Errorf("letter '%v' is not in alphabet", l))
m.done <- laststate{s, errors}
return
panic(fmt.Sprintf("letter '%v' is not in alphabet", l))
}
// Compose the domain element, so that the co-domain
// element can be found via the transition function.
Expand All @@ -212,43 +189,34 @@ func (m *DFA) Run(init interface{}) (State, error) {
if coe := m.d[de]; coe != nil {
s = coe.s
switch exec := coe.exec.(type) {
case func() error:
case func():
m.logger(s)
if err := exec(); err != nil {
errors = append(errors, err)
}
case func() (Letter, error):
exec()
case func() Letter:
m.logger(s)
if l, err := exec(); err != nil {
errors = append(errors, err)
m.input = &l
} else {
m.input = &l
}
l := exec()
m.input = &l
}
if m.f[s] {
// If the new state is a terminal state then
// the DFA has accepted the input sequence
// and it can stop.
m.done <- laststate{s, errors}
m.done <- laststate{s, true}
return
}
} else {
// Otherwise stop the DFA with a rejected state,
// the DFA has rejected the input sequence.
errors = append(errors, fmt.Errorf("no state transition for input '%v' from '%v'", l, s))
m.done <- laststate{s, errors}
return
panic(fmt.Sprintf("no state transition for input '%v' from '%v'", l, s))
}
}
}
// The caller has closed the input channel, check if the
// current state is accepted or rejected by the DFA.
if m.f[s] {
m.done <- laststate{s, errors}
m.done <- laststate{s, true}
} else {
errors = append(errors, fmt.Errorf("state '%v' is not terminal", s))
m.done <- laststate{s, errors}
m.done <- laststate{s, false}
}
}()
return m.result()
Expand Down Expand Up @@ -278,11 +246,7 @@ func (m *DFA) GraphViz() string {
return buf.String()
}

func (m *DFA) result() (State, error) {
func (m *DFA) result() (State, bool) {
t := <-m.done
if len(t.errors) == 0 {
return t.s, nil
} else {
return t.s, t.errors
}
}
return t.s, t.accepted
}
66 changes: 11 additions & 55 deletions dfa_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -22,20 +22,19 @@ type Exec struct {
cmu *sync.Mutex
}

func (e *Exec) Next() (Letter, error) {
func (e *Exec) Next() Letter {
e.cmu.Lock()
defer e.cmu.Unlock()
l := e.Sequence[0]
e.Sequence = e.Sequence[1:]
e.nextCount++
return l, nil
return l
}

func (e *Exec) Last() error {
func (e *Exec) Last() {
e.cmu.Lock()
defer e.cmu.Unlock()
e.lastCount++
return nil
}

func (e *Exec) NextCount() int {
Expand Down Expand Up @@ -117,9 +116,9 @@ func TestSimple(t *testing.T) {
d.SetTransition(Resending, SendFailure, Resending, e.Next)
d.SetTransition(Resending, ExitWanted, Exiting, e.Last)

final, err := d.Run(e.Next)
if err != nil {
t.Fatalf("failed to run dfa: %v", err)
final, accepted := d.Run(e.Next)
if !accepted {
t.Fatalf("failed to recognize Exiting or Terminating as terminal state")
}

if final != Exiting {
Expand Down Expand Up @@ -151,9 +150,9 @@ func TestLastState(t *testing.T) {
// The expectation is that the Next nor Last method will
// ever be called since the DFA's starting and terminal
// state are the same.
final, err := d.Run(e.Next)
if err != nil {
t.Fatalf("failed to run dfa: %v", err)
final, accepted := d.Run(e.Next)
if !accepted {
t.Fatalf("failed to recognize Starting as terminal state")
}
if final != Starting {
t.Fatalf("final state should have been: %v, but was: %v", Starting, final)
Expand Down Expand Up @@ -189,8 +188,8 @@ func TestGraphViz(t *testing.T) {
d.SetStartState(Starting)
d.SetTerminalStates(Exiting, Terminating)

next := func() (Letter, error) { return Exit, nil }
exit := func() error { return nil }
next := func() Letter { return Exit }
exit := func() {}

d.SetTransition(Starting, EverybodyStarted, Running, next)
d.SetTransition(Starting, Failure, Exiting, exit)
Expand Down Expand Up @@ -240,46 +239,3 @@ func TestGraphViz(t *testing.T) {
t.Fatalf("expected string: `%v`", `"finishing" -> "exiting"[label="exit"];`)
}
}

func TestErrors(t *testing.T) {
// States
Starting := State("starting")
Running := State("running")
Exiting := State("exiting")
// Letters
Failure := Letter("failure")
Success := Letter("success")

d := New()
d.SetStartState(Starting)
d.SetTerminalStates(Exiting)

starting := func() (Letter, error) { return Success, nil }
running := func() (Letter, error) { return Failure, fmt.Errorf("error from running") }
exiting := func() error { return fmt.Errorf("error from exiting") }

d.SetTransition(Starting, Success, Running, running)
d.SetTransition(Starting, Failure, Exiting, exiting)

d.SetTransition(Running, Success, Exiting, exiting)
d.SetTransition(Running, Failure, Exiting, exiting)

final, err := d.Run(starting)
if err == nil {
t.Fatalf("expected non-nil error")
}
if final != Exiting {
t.Fatalf("expected final state to be Exiting")
}
switch err := err.(type) {
case Errors:
if "error from running" != err[0].Error() {
t.Fatalf("expected 1st error to be 'error from running'")
}
if "error from exiting" != err[1].Error() {
t.Fatalf("expected 2nd error to be 'error from exiting'")
}
default:
t.Fatalf("expected error of type Errors")
}
}

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