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|
package subex
import (
"main/walk"
)
// Where slots are stored
type Store map[rune][]walk.Atom
// Return a new store with all the data from this one
func (store Store) clone() Store {
newStore := make(Store)
for key, val := range store {
newStore[key] = val
}
return newStore
}
// Return a copy of this store but with an additional slot set
func (store Store) withValue(key rune, value []walk.Atom) Store {
newStore := store.clone()
newStore[key] = value
return newStore
}
// Compile the SubexAST into a transducer SubexState that can be run
func CompileTransducer(transducerAst SubexAST) SubexState {
return transducerAst.compileWith(&SubexNoneState{})
}
// An immutable stack for outputting to
type OutputStack interface {
pop() ([]walk.Atom, OutputStack)
push(atoms []walk.Atom) OutputStack
}
type OutputStackNil struct {}
func (stack OutputStackNil) pop() ([]walk.Atom, OutputStack) {
panic("Tried to pop from an empty OutputStack")
}
func (stack OutputStackNil) push(atoms []walk.Atom) OutputStack {
return &OutputStackCons {
head: atoms,
tail: stack,
}
}
type OutputStackCons struct {
head []walk.Atom
tail OutputStack
}
func (stack OutputStackCons) pop() ([]walk.Atom, OutputStack) {
return stack.head, stack.tail
}
func (stack OutputStackCons) push(atoms []walk.Atom) OutputStack {
return &OutputStackCons {
head: atoms,
tail: stack,
}
}
func topAppend(outputStack OutputStack, atoms []walk.Atom) OutputStack {
head, tail := outputStack.pop()
return tail.push(walk.ConcatData(head, atoms))
}
// One branch of subex execution
type SubexBranch struct {
// Content of slots in this branch
store Store
// State in this branch
state SubexState
// The output stack. At the end of the program, whatever is on top of this will be output
// States may push or pop to the stack as they wish, creating sort of a call stack that allows states to capture the output of other states
outputStack OutputStack
}
// Read a single character and return all the branches resulting from this branch consuming it
func (pair SubexBranch) eat(char walk.Atom) []SubexBranch {
return pair.state.eat(pair.store, pair.outputStack, char)
}
func (pair SubexBranch) accepting() []OutputStack {
return pair.state.accepting(pair.store, pair.outputStack)
}
func equalStates(left SubexBranch, right SubexBranch) bool {
// Only care about if they are the same pointer
return left.state == right.state
}
// If two branches have the same state, only the first has a chance of being successful
// This function removes all of the pointless execution branches to save execution time
func pruneStates(states []SubexBranch) (newStates []SubexBranch) {
outer: for _, state := range states {
for _, newState := range newStates {
if equalStates(state, newState) {
continue outer
}
}
newStates = append(newStates, state)
}
return newStates
}
// Run the subex transducer
func RunTransducer(transducer SubexState, input []walk.Atom) (output []walk.Atom, err bool) {
states := []SubexBranch{{
state: transducer,
outputStack: OutputStackNil{}.push(nil),
store: make(Store),
}}
for _, piece := range input {
var newStates []SubexBranch
for _, state := range states {
newStates = append(newStates, state.eat(piece)...)
}
states = pruneStates(newStates)
}
for _, state := range states {
acceptingStacks := state.accepting()
for _, stack := range acceptingStacks {
output, _ := stack.pop()
return output, false
}
}
return nil, true
}
|
