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compute.go
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compute.go
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package compute
import (
"errors"
"go/scanner"
"go/token"
"strconv"
"strings"
)
import (
"github.com/alfredxing/calc/constants"
"github.com/alfredxing/calc/operators"
"github.com/alfredxing/calc/operators/functions"
)
var resHistory = []float64{}
// ClearHistory removes prior evaluation history used for @ references.
func ClearHistory() {
resHistory = []float64{}
}
func Evaluate(in string) (float64, error) {
floats := NewFloatStack()
ops := NewStringStack()
s := initScanner(in)
var prev token.Token = token.ILLEGAL
var back int = -1
ScanLoop:
for {
_, tok, lit := s.Scan()
if lit != "@" && back > -1 && len(resHistory) > 0 {
if hval, err := getHistory(back); err != nil {
return 0, err
} else {
floats.Push(hval)
}
if prev == token.RPAREN || constants.IsConstant(prev.String()) {
evalUnprecedenced("*", ops, floats)
}
back = -1
}
switch {
case tok == token.EOF:
break ScanLoop
case lit == "@":
back += 1
case constants.IsConstant(lit):
floats.Push(constants.GetValue(lit))
if prev == token.RPAREN || isOperand(prev) {
evalUnprecedenced("*", ops, floats)
}
case isOperand(tok):
val, err := parseFloat(lit)
if err != nil {
return 0, err
}
floats.Push(val)
if prev == token.RPAREN || constants.IsConstant(prev.String()) {
evalUnprecedenced("*", ops, floats)
}
case functions.IsFunction(lit):
if isOperand(prev) || prev == token.RPAREN {
evalUnprecedenced("*", ops, floats)
}
ops.Push(lit)
case isOperator(tok.String()):
op := tok.String()
if isNegation(tok, prev) {
op = "neg"
}
evalUnprecedenced(op, ops, floats)
case tok == token.LPAREN:
if isOperand(prev) {
evalUnprecedenced("*", ops, floats)
}
ops.Push(tok.String())
case tok == token.RPAREN:
for ops.Pos >= 0 && ops.SafeTop() != "(" {
err := evalOp(ops.SafePop(), floats)
if err != nil {
return 0, err
}
}
_, err := ops.Pop()
if err != nil {
return 0, errors.New("Can't find matching parenthesis!")
}
if ops.Pos >= 0 {
if functions.IsFunction(ops.SafeTop()) {
err := evalOp(ops.SafePop(), floats)
if err != nil {
return 0, err
}
}
}
case tok == token.SEMICOLON:
default:
inspect := tok.String()
if strings.TrimSpace(lit) != "" {
inspect += " (`" + lit + "`)"
}
return 0, errors.New("Unrecognized token " + inspect + " in expression")
}
prev = tok
}
for ops.Pos >= 0 {
op, _ := ops.Pop()
err := evalOp(op, floats)
if err != nil {
return 0, err
}
}
res, err := floats.Top()
if err != nil {
return 0, errors.New("Expression could not be parsed!")
}
pushHistory(res)
return res, nil
}
func evalUnprecedenced(op string, ops *StringStack, floats *FloatStack) {
for ops.Pos >= 0 && shouldPopNext(op, ops.SafeTop()) {
evalOp(ops.SafePop(), floats)
}
ops.Push(op)
}
func shouldPopNext(n1 string, n2 string) bool {
if !isOperator(n2) {
return false
}
if n1 == "neg" {
return false
}
op1 := parseOperator(n1)
op2 := parseOperator(n2)
if op1.Associativity == operators.L {
return op1.Precedence <= op2.Precedence
}
return op1.Precedence < op2.Precedence
}
func evalOp(opName string, floats *FloatStack) error {
op := operators.FindOperatorFromString(opName)
if op == nil {
return errors.New("Either unmatched paren or unrecognized operator")
}
var args = make([]float64, op.Args)
for i := op.Args - 1; i >= 0; i-- {
arg, err := floats.Pop()
if err != nil {
return errors.New("Not enough arguments to operator!")
}
args[i] = arg
}
floats.Push(op.Operation(args))
return nil
}
func isOperand(tok token.Token) bool {
return tok == token.FLOAT || tok == token.INT
}
func isOperator(lit string) bool {
return operators.IsOperator(lit)
}
func isNegation(tok token.Token, prev token.Token) bool {
return tok == token.SUB &&
(prev == token.ILLEGAL || isOperator(prev.String()) || prev == token.LPAREN)
}
func parseFloat(lit string) (float64, error) {
f, err := strconv.ParseFloat(lit, 64)
if err != nil {
return 0, errors.New("Cannot parse recognized float: " + lit)
}
return f, nil
}
func parseOperator(lit string) *operators.Operator {
return operators.FindOperatorFromString(lit)
}
func getHistory(back int) (float64, error) {
if back >= len(resHistory) {
return 0, errors.New("History underflow")
}
return resHistory[back], nil
}
func pushHistory(res float64) {
resHistory = append([]float64{res}, resHistory...)
}
func initScanner(in string) scanner.Scanner {
var s scanner.Scanner
src := []byte(in)
fset := token.NewFileSet()
file := fset.AddFile("", fset.Base(), len(src))
s.Init(file, src, nil, 0)
return s
}