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lisp.groovy
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lisp.groovy
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kLPar = '('
kRPar = ')'
kQuote = "'"
kNil = [tag: 'nil', data: 'nil']
def safeCar(obj) {
if (obj['tag'] == 'cons') {
return obj['car']
}
return kNil
}
def safeCdr(obj) {
if (obj['tag'] == 'cons') {
return obj['cdr']
}
return kNil
}
def makeError(str) {
return [tag: 'error', data: str]
}
sym_table = [:]
def makeSym(str) {
if (str == 'nil') {
return kNil
} else if (!sym_table[str]) {
sym_table[str] = [tag: 'sym', data: str]
}
return sym_table[str]
}
def makeNum(num) {
return [tag: 'num', data: num]
}
def makeCons(a, d) {
return [tag: 'cons', car: a, cdr: d]
}
def makeSubr(fn) {
return [tag: 'subr', data: fn]
}
def makeExpr(args, env) {
return [tag: 'expr', args: safeCar(args), body: safeCdr(args), env: env]
}
def nreverse(lst) {
def ret = kNil
while (lst['tag'] == 'cons') {
def tmp = lst['cdr']
lst['cdr'] = ret
ret = lst
lst = tmp
}
return ret
}
def pairlis(lst1, lst2) {
def ret = kNil
while (lst1['tag'] == 'cons' && lst2['tag'] == 'cons') {
ret = makeCons(makeCons(lst1['car'], lst2['car']), ret)
lst1 = lst1['cdr']
lst2 = lst2['cdr']
}
return nreverse(ret)
}
def isDelimiter(c) {
return c == kLPar || c == kRPar || c == kQuote || c ==~ /\s+/
}
def skipSpaces(str) {
return str.replaceFirst(/^\s+/, '')
}
def makeNumOrSym(str) {
if (str ==~ /^-?\d+$/) {
return makeNum(str.toInteger())
}
return makeSym(str)
}
def readAtom(str) {
def next = ''
for (i = 0; i < str.size(); i++) {
if (isDelimiter(str[i])) {
next = str[i..-1]
str = str[0..i-1]
break
}
}
return [makeNumOrSym(str), next]
}
def rest(str, i) {
// rest('a', 1) => '' ('a'[1..-1] causes an out of range error)
if (str.size() <= i) {
return ''
}
return str[i..-1]
}
def read(str) {
str = skipSpaces(str)
if (str == '') {
return [makeError('empty input'), '']
} else if (str[0] == kRPar) {
return [makeError('invalid syntax: ' + str), '']
} else if (str[0] == kLPar) {
return readList(rest(str, 1))
} else if (str[0] == kQuote) {
def tmp = read(rest(str, 1))
return [makeCons(makeSym('quote'), makeCons(tmp[0], kNil)), tmp[1]]
}
return readAtom(str)
}
def readList(str) {
def ret = kNil
while (true) {
str = skipSpaces(str)
if (str == '') {
return [makeError('unfinished parenthesis'), '']
} else if (str[0] == kRPar) {
break
}
def tmp = read(str)
def elm = tmp[0]
def next = tmp[1]
if (elm['tag'] == 'error') {
return [elm, '']
}
ret = makeCons(elm, ret)
str = next
}
return [nreverse(ret), rest(str, 1)]
}
def printObj(obj) {
if (obj['tag'] == 'num' || obj['tag'] == 'sym' || obj['tag'] == 'nil') {
return obj['data'].toString()
} else if (obj['tag'] == 'error') {
return '<error: ' + obj['data'] + '>'
} else if (obj['tag'] == 'cons') {
return printList(obj)
} else if (obj['tag'] == 'subr' || obj['tag'] == 'expr') {
return '<' + obj['tag'] + '>'
}
return '<unknown>'
}
def printList(obj) {
def ret = ''
def first = true
while (obj['tag'] == 'cons') {
if (first) {
first = false
} else {
ret += ' '
}
ret += printObj(obj['car'])
obj = obj['cdr']
}
if (obj['tag'] == 'nil') {
return '(' + ret + ')'
}
return '(' + ret + ' . ' + printObj(obj) + ')'
}
def findVar(sym, env) {
while (env['tag'] == 'cons') {
def alist = env['car']
while (alist['tag'] == 'cons') {
if (alist['car']['car'].is(sym)) {
return alist['car']
}
alist = alist['cdr']
}
env = env['cdr']
}
return kNil
}
g_env = makeCons(kNil, kNil)
def addToEnv(sym, val, env) {
env['car'] = makeCons(makeCons(sym, val), env['car'])
}
def eval(obj, env) {
def tag = obj['tag']
if (tag == 'nil' || tag == 'num' || tag == 'error') {
return obj
} else if (tag == 'sym') {
def bind = findVar(obj, env)
if (bind.is(kNil)) {
return makeError(obj['data'] + ' has no value')
}
return bind['cdr']
}
def op = safeCar(obj)
def args = safeCdr(obj)
if (op.is(makeSym('quote'))) {
return safeCar(args)
} else if (op.is(makeSym('if'))) {
if (eval(safeCar(args), env).is(kNil)) {
return eval(safeCar(safeCdr(safeCdr(args))), env)
}
return eval(safeCar(safeCdr(args)), env)
} else if (op.is(makeSym('lambda'))) {
return makeExpr(args, env)
} else if (op.is(makeSym('defun'))) {
def expr = makeExpr(safeCdr(args), env)
def sym = safeCar(args)
addToEnv(sym, expr, g_env)
return sym
} else if (op.is(makeSym('setq'))) {
def val = eval(safeCar(safeCdr(args)), env)
def sym = safeCar(args)
def bind = findVar(sym, env)
if (bind.is(kNil)) {
addToEnv(sym, val, g_env)
} else {
bind['cdr'] = val
}
return val
}
return apply(eval(op, env), evlis(args, env), env)
}
def evlis(lst, env) {
def ret = kNil
while (lst['tag'] == 'cons') {
def elm = eval(lst['car'], env)
if (elm['tag'] == 'error') {
return elm
}
ret = makeCons(elm, ret)
lst = lst['cdr']
}
return nreverse(ret)
}
def progn(body, env) {
def ret = kNil
while (body['tag'] == 'cons') {
ret = eval(body['car'], env)
body = body['cdr']
}
return ret
}
def apply(fn, args, env) {
if (fn['tag'] == 'error') {
return fn
} else if (args['tag'] == 'error') {
return args
} else if (fn['tag'] == 'subr') {
return fn['data'](args)
} else if (fn['tag'] == 'expr') {
return progn(fn['body'], makeCons(pairlis(fn['args'], args), fn['env']))
}
return makeError('noimpl')
}
def subrCar = {
return safeCar(safeCar(it))
}
def subrCdr = {
return safeCdr(safeCar(it))
}
def subrCons = {
return makeCons(safeCar(it), safeCar(safeCdr(it)))
}
def subrEq = {
def x = safeCar(it)
def y = safeCar(safeCdr(it))
if (x['tag'] == 'num' && x['tag'] == 'num') {
if (x['data'] == y['data']) {
return makeSym('t')
}
return kNil
} else if (x.is(y)) {
return makeSym('t')
}
return kNil
}
def subrAtom = {
if (safeCar(it)['tag'] == 'cons') {
return kNil
}
return makeSym('t')
}
def subrNumberp = {
if (safeCar(it)['tag'] == 'num') {
return makeSym('t')
}
return kNil
}
def subrSymbolp = {
if (safeCar(it)['tag'] == 'sym') {
return makeSym('t')
}
return kNil
}
def subrAddOrMul(fn, init_val) {
return {
def ret = init_val
while (it['tag'] == 'cons') {
if (it['car']['tag'] != 'num') {
return makeError('wrong type')
}
ret = fn(ret, it['car']['data'])
it = it['cdr']
}
return makeNum(ret)
}
}
def subrAdd = subrAddOrMul({x, y -> x + y}, 0)
def subrMul = subrAddOrMul({x, y -> x * y}, 1)
def subrSubOrDivOrMod(fn) {
return {
x = safeCar(it)
y = safeCar(safeCdr(it))
if (x['tag'] != 'num' || y['tag'] != 'num') {
return makeError('wrong type')
}
return makeNum(fn(x['data'], y['data']))
}
}
def subrSub = subrSubOrDivOrMod({x, y -> x - y})
def subrDiv = subrSubOrDivOrMod({x, y -> x / y})
def subrMod = subrSubOrDivOrMod({x, y -> x % y})
addToEnv(makeSym('car'), makeSubr(subrCar), g_env)
addToEnv(makeSym('cdr'), makeSubr(subrCdr), g_env)
addToEnv(makeSym('cons'), makeSubr(subrCons), g_env)
addToEnv(makeSym('eq'), makeSubr(subrEq), g_env)
addToEnv(makeSym('atom'), makeSubr(subrAtom), g_env)
addToEnv(makeSym('numberp'), makeSubr(subrNumberp), g_env)
addToEnv(makeSym('symbolp'), makeSubr(subrSymbolp), g_env)
addToEnv(makeSym('+'), makeSubr(subrAdd), g_env)
addToEnv(makeSym('*'), makeSubr(subrMul), g_env)
addToEnv(makeSym('-'), makeSubr(subrSub), g_env)
addToEnv(makeSym('/'), makeSubr(subrDiv), g_env)
addToEnv(makeSym('mod'), makeSubr(subrMod), g_env)
addToEnv(makeSym('t'), makeSym('t'), g_env)
def ireader = new InputStreamReader(System.in)
def breader = new BufferedReader(ireader)
print('> ')
System.out.flush()
while ((line = breader.readLine()) != null) {
println(printObj(eval(read(line)[0], g_env)))
print('> ')
System.out.flush()
}