move master to main #1
1 changed files with 158 additions and 2 deletions
160
forth/eval.go
160
forth/eval.go
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@ -2,17 +2,173 @@
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package main
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import (
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"errors"
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"strconv"
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"strings"
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)
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type Evaluator struct {
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stack []int
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words map[string](func() error)
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}
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func (e *Evaluator) push(n int) {
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e.stack = append(e.stack, n)
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}
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func (e *Evaluator) pop() (int, error) {
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size := len(e.stack)
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if size == 0 {
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return 0, errors.New("nothing to pop")
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}
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n := e.stack[size-1]
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e.stack = e.stack[:size-1]
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return n, nil
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}
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func (e *Evaluator) popTwo() (int, int, error) {
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if len(e.stack) < 2 {
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return 0, 0, errors.New("not enough elements on stack")
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}
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second, _ := e.pop()
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first, _ := e.pop()
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return first, second, nil
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}
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// Used to initialzie arithemtic operations in words map
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func (e *Evaluator) arithmeticOp(op func(int, int) int) func() error {
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return func() error {
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a, b, err := e.popTwo()
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if err != nil {
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return errors.New("not enough elements on stack")
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}
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e.push(op(a, b))
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return nil
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}
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}
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func (e *Evaluator) initBasicWords() {
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e.words["+"] = e.arithmeticOp(func(a, b int) int { return a + b })
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e.words["-"] = e.arithmeticOp(func(a, b int) int { return a - b })
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e.words["*"] = e.arithmeticOp(func(a, b int) int { return a * b })
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e.words["/"] = func() error {
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a, b, err := e.popTwo()
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if err != nil {
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return errors.New("not enough elements on stack")
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}
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if b == 0 {
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return errors.New("division by zero")
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}
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e.push(a / b)
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return nil
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}
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e.words["dup"] = func() error {
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size := len(e.stack)
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if size == 0 {
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return errors.New("not enough elements on stack")
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}
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e.stack = append(e.stack, e.stack[size-1])
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return nil
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}
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e.words["over"] = func() error {
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size := len(e.stack)
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if size < 2 {
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return errors.New("not enough elements on stack")
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}
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e.stack = append(e.stack, e.stack[size-2])
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return nil
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}
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e.words["drop"] = func() error {
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_, err := e.pop()
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return err
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}
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e.words["swap"] = func() error {
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size := len(e.stack)
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if size < 2 {
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return errors.New("not enough elements on stack")
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}
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e.stack[size-1], e.stack[size-2] = e.stack[size-2], e.stack[size-1]
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return nil
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}
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}
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func (e *Evaluator) getFunc(word string) (func() error, error) {
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call, found := e.words[word]
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if found {
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return call, nil
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}
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num, err := strconv.Atoi(word)
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if err != nil {
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return nil, errors.New("word is not numerical or is not defined")
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}
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call = func() error {
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e.push(num)
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return nil
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}
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return call, nil
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}
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func (e *Evaluator) defineWord(word string, def string) error {
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_, err := strconv.Atoi(word)
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if err == nil {
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return errors.New("word definition must not be numeric")
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}
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definitionWords := strings.Fields(def)
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callChain := make([](func() error), len(definitionWords))
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for i, w := range definitionWords {
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call, err := e.getFunc(w)
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if err != nil {
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return err
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}
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callChain[i] = call
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}
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e.words[word] = func() error {
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for _, call := range callChain {
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err := call()
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if err != nil {
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return err
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}
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}
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return nil
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}
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return nil
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}
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// NewEvaluator creates evaluator.
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func NewEvaluator() *Evaluator {
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return &Evaluator{}
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eval := &Evaluator{make([]int, 0), make(map[string](func() error))}
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eval.initBasicWords()
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return eval
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}
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// Process evaluates sequence of words or definition.
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//
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// Returns resulting stack state and an error.
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func (e *Evaluator) Process(row string) ([]int, error) {
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return nil, nil
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row = strings.ToLower(row)
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if strings.HasPrefix(row, ":") && strings.HasSuffix(row, ";") {
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row = strings.Trim(row, " :;")
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wordAndDef := strings.SplitN(row, " ", 2)
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if len(wordAndDef) < 2 {
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return e.stack, errors.New("couldn't define a new word - incorrect syntax")
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}
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word, def := wordAndDef[0], wordAndDef[1]
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err := e.defineWord(word, def)
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if err != nil {
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return e.stack, err
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}
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return e.stack, nil
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}
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for _, word := range strings.Fields(row) {
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call, err := e.getFunc(word)
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if err != nil {
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return e.stack, err
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}
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err = call()
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if err != nil {
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return e.stack, err
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}
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}
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return e.stack, nil
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}
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