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main.go
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// Copyright 2014 SteelSeries ApS. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This package impliments a basic LISP interpretor for embedding in a go program for scripting.
// This file provides a repl
package main
import (
"errors"
"fmt"
. "github.com/steelseries/golisp"
"math"
"math/big"
"os"
"path/filepath"
"regexp"
"strings"
)
func loadLispFile(filename string, fileInfo os.FileInfo, err error) error {
match, _ := filepath.Match("*.lsp", fileInfo.Name())
if match {
_, err = ProcessFile(filename)
if err != nil {
err = errors.New(fmt.Sprintf("Error GoLisp file: '%s': %s", fileInfo.Name(), err))
}
}
return err
}
func loadLispCode() {
err := filepath.Walk("./lisp", loadLispFile)
if err != nil {
panic(err)
}
}
//============================ EVALUATOR
var whitespace_rx = regexp.MustCompile(`\s+`)
var fp_rx = regexp.MustCompile(`(\d+(?:\.\d+)?)`) // simple fp number
var func_rx = regexp.MustCompile(`([a-zA-Z\-\_]+)`)
var operators = "-+**/<>"
// prec returns the operator's precedence
func prec(op string) (result int) {
if op == "-" || op == "+" {
result = 1
} else if op == "*" || op == "/" {
result = 2
} else if op == "**" {
result = 3
}
return
}
// opGTE returns true if op1's precedence is >= op2
func opGTE(op1, op2 string) bool {
return prec(op1) >= prec(op2)
}
// isOperator returns true if token is an operator
func isOperator(token string) bool {
return strings.Contains(operators, token)
}
// isOperand returns true if token is an operand
func isOperand(token string) bool {
return fp_rx.MatchString(token)
}
// isLispFunction returns true if token is the name of a function in
// the lisp global symbol table
func isLispFunction(token string) bool {
return func_rx.MatchString(token)
}
// convert2postfix converts an infix expression to postfix
func convert2postfix(tokens []string) (result []string, err error) {
var stack Stack
var functions Stack
for _, token := range tokens {
if isLispFunction(token) {
f := Global.ValueOf(SymbolWithName(token))
if NilP(f) {
err = errors.New(fmt.Sprintf("No function named %s", token))
return
} else if !FunctionP(f) && !PrimitiveP(f) {
err = errors.New(fmt.Sprintf("%s is not a function", token))
return
} else {
functions.Push(token)
}
} else if token == "," {
} else if isOperator(token) {
OPERATOR:
for {
top, err := stack.Top()
if err == nil && top != "(" {
if opGTE(top.(string), token) {
pop, _ := stack.Pop()
result = append(result, pop.(string))
} else {
break OPERATOR
}
}
break OPERATOR
}
stack.Push(token)
} else if token == "(" {
stack.Push(token)
} else if token == ")" {
PAREN:
for {
top, err := stack.Top()
if err == nil && top != "(" {
pop, _ := stack.Pop()
result = append(result, pop.(string))
} else {
stack.Pop() // pop off "("
if !functions.IsEmpty() {
f, _ := functions.Pop()
result = append(result, f.(string))
}
break PAREN
}
}
} else if isOperand(token) {
result = append(result, token)
}
}
for !stack.IsEmpty() {
pop, _ := stack.Pop()
result = append(result, pop.(string))
}
return
}
// evaluatePostfix takes a postfix expression and evaluates it
func evaluatePostfix(postfix []string) (*big.Rat, error) {
var stack Stack
result := new(big.Rat) // note: a new(big.Rat) has value "0/1" ie zero
for _, token := range postfix {
if isOperand(token) {
bigrat := new(big.Rat)
if _, err := fmt.Sscan(token, bigrat); err != nil {
return nil, fmt.Errorf("unable to scan %s", token)
}
stack.Push(bigrat)
} else if isOperator(token) {
op2, err2 := stack.Pop()
if err2 != nil {
return nil, err2
}
op1, err1 := stack.Pop()
if err1 != nil {
return nil, err1
}
dummy := new(big.Rat)
switch token {
case "**":
float1 := BigratToFloat(op1.(*big.Rat))
float2 := BigratToFloat(op2.(*big.Rat))
float_result := math.Pow(float1, float2)
stack.Push(FloatToBigrat(float_result))
case "*":
result := dummy.Mul(op1.(*big.Rat), op2.(*big.Rat))
stack.Push(result)
case "/":
result := dummy.Quo(op1.(*big.Rat), op2.(*big.Rat))
stack.Push(result)
case "+":
result = dummy.Add(op1.(*big.Rat), op2.(*big.Rat))
stack.Push(result)
case "-":
result = dummy.Sub(op1.(*big.Rat), op2.(*big.Rat))
stack.Push(result)
case "<":
if op1.(*big.Rat).Cmp(op2.(*big.Rat)) <= -1 {
stack.Push(big.NewRat(1, 1))
} else {
stack.Push(new(big.Rat))
}
case ">":
if op1.(*big.Rat).Cmp(op2.(*big.Rat)) >= 1 {
stack.Push(big.NewRat(1, 1))
} else {
stack.Push(new(big.Rat))
}
}
} else if isLispFunction(token) {
//"(<token> <float1> <float2>...)"
f := Global.ValueOf(SymbolWithName(token))
var numberOfArgs = 0
if TypeOf(f) == FunctionType {
numberOfArgs = FunctionValue(f).RequiredArgCount
} else if TypeOf(f) == PrimitiveType {
n, _ := fmt.Sscanf(PrimitiveValue(f).NumberOfArgs, "%d", &numberOfArgs)
if n != 1 {
return nil, fmt.Errorf("Only functions with a fixed arity can be used, %s has artiy of %s", token, PrimitiveValue(f).NumberOfArgs)
}
}
var args []*Data
// collect args
for i := 0; i < numberOfArgs; i++ {
op, err := stack.Pop()
if err != nil {
return nil, err
}
float := BigratToFloat(op.(*big.Rat))
args = append(args, FloatWithValue(float32(float)))
}
val, err := Apply(f, Reverse(ArrayToList(args)), Global)
if err != nil {
return nil, err
}
result = FloatToBigrat(float64(FloatValue(val)))
stack.Push(result)
} else {
return nil, fmt.Errorf("unknown token %v", token)
}
}
retval, err := stack.Pop()
if err != nil {
return nil, err
}
return retval.(*big.Rat), nil
}
// tokenise takes an expr string and converts it to a slice of tokens
//
// tokenise puts spaces around all non-numbers, removes leading and
// trailing spaces, then splits on spaces
//
func tokenise(expr string) []string {
spaced := fp_rx.ReplaceAllString(expr, " ${1} ")
symbols := []string{"(", ")", ","}
for _, symbol := range symbols {
spaced = strings.Replace(spaced, symbol, fmt.Sprintf(" %s ", symbol), -1)
}
stripped := whitespace_rx.ReplaceAllString(strings.TrimSpace(spaced), "|")
return strings.Split(stripped, "|")
}
// Eval takes an infix string arithmetic expression, and evaluates it
//
// Usage:
// result, err := evaler.Eval("1+2")
// Returns: the result of the evaluation, and any errors
//
func EvalEquation(expr string) (result *big.Rat, err error) {
defer func() {
if e := recover(); e != nil {
result = nil
err = fmt.Errorf("Invalid Expression: %s", expr)
}
}()
tokens := tokenise(expr)
// fmt.Printf("tokens: %v\n", tokens)
postfix, err := convert2postfix(tokens)
// fmt.Printf("postfix: %v\n", postfix)
if err != nil {
return
}
return evaluatePostfix(postfix)
}
func ioLoop() {
fmt.Printf("Welcome to the GoLisp Example\n")
fmt.Printf("Copyright 2014 SteelSeries\n")
fmt.Printf("Evaluate 'quit' to exit.\n\n")
prompt := "> "
LoadHistoryFromFile(".golisp_history")
lastInput := ""
for true {
input := *ReadLine(&prompt)
if input == "quit" {
return
} else if input != "" {
if input != lastInput {
AddHistory(input)
}
lastInput = input
result, err := EvalEquation(input)
if err != nil {
fmt.Printf("Error in evaluation: %s\n", err)
} else {
fmt.Printf("==> %v\n", result)
}
}
}
}
func main() {
loadLispCode()
ioLoop()
}