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translate.js
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translate.js
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// translate.js
// Functions to create an abstract syntax tree from an array of Scheme tokens.
var predicates = require('./predicates.js');
var assert = require('assert');
var lexer = require('./lexer');
var tokenize = lexer.tokenize;
var parser = require('./parser');
// debugging
var print = console.log;
// null 'equals' [], that is they should be interchangable
////////////////////////////////////////////////////////////////////////////////
// for traversing the AST
function car(sexp) {
if (sexp.length) {
return sexp[0];
} else {
return false;
}
}
function cdr(sexp) {
var cdr_sexp;
if (sexp.length >= 2) {
cdr_sexp = sexp.slice();
cdr_sexp.splice(0, 1);
return cdr_sexp;
} else {
return false;
}
}
function cons(exp1, exp2) {
// returns a new copy of the consed pair
var new_exp;
if (predicates.is_array(exp2)) {
new_exp = exp2.slice();
new_exp.unshift(exp1);
return new_exp;
} else {
return false;
}
}
////////////////////////////////////////////////////////////////////////////////
//
function ast_to_js(sexp, env) {
// TODO: - use is_within_env instead of a series of ifs
// - lowercase the car(sexp)
// - if an atom or a sexp is quoted ['QUOTE', 9] <= '9 and ['QUOTE', [9, 4, null]] <= '(9 4)
var i; // for loop counter
var tmp_js = []; // placeholder for evaluated JS
debugger;
if (predicates.is_array(sexp)) {
if (bindings[car(sexp)]) {
return bindings[car(sexp)](cdr(sexp), env); // Added env to bindings in generate math_operator
} else if (((sexp.length === 2)) && (sexp[1] === null)) { // a list of one value, not in bindings
return ast_to_js(car(sexp), env);
} else if (env.hasOwnProperty(car(sexp))) {
// if this is an expression and car(sexp) is in env, pass as a procedure
if (env[car(sexp)] === "tmp") { // function calling itself
// multiple arguments to function calling itself recursively
if (cdr(sexp).length > 2) {
for (i=0; i<cdr(sexp).length; i++) {
if (cdr(sexp)[i] === null) {
continue;
} else {
tmp_js.push(ast_to_js(cdr(sexp)[i], env));
}
}
return car(sexp) + "(" + tmp_js.join(",") + ")";
}
// a single argument
return car(sexp) + "(" + ast_to_js(car(cdr(sexp)), env) + ")";
} else {
return env[car(sexp)](cdr(sexp), env); // NEEDS TESTS!!!
}
} else if (bindings.hasOwnProperty(car(car(sexp)))) { // probably a lambda with arguments
return bindings[car(car(sexp))](car(sexp), env, cdr(sexp));
} else {
throw new Error('in ' + sexp + ' ' + car(sexp) + ' not supported');
}
} else if (env.hasOwnProperty(sexp)) {
return sexp; // return the variable name; value is in env
} else if (predicates.is_number(sexp)) {
return sexp;
} else if (predicates.is_quoted_twice(sexp)) {
return sexp; // a string???
} else if (sexp === null) {
return '';
} else {
// return "TYPE NOT FOUND";
return sexp;
}
}
function translate_let(lexp, env) {
// has to return last value
var local_bindings = car(lexp);
var expression_list = cdr(lexp);
var i; // index for each elem in local_bindings and expression_list
var let_expression = 'function() {';
var vinit;
for (vinit in local_bindings) {
if (local_bindings[vinit] !== null) {
local_bindings[vinit].unshift('define');
let_expression += ast_to_js(local_bindings[vinit], env);
}
}
// evaluate expression
for (i=0; i<expression_list.length - 1; i++) {
if (i === (expression_list.length - 2)) {
let_expression += "return " + ast_to_js(expression_list[i], env) + ";}();";
} else {
let_expression += ast_to_js(expression_list[i], env) + ";";
}
}
return let_expression;
}
function lambda(lexp, env, lambda_args) {
// lambda in bindings
var lambda_statement = ''; // the JavaScript translation
var lambda_expression; // the lambda expression
var lambda_var_args; // the variable arguments passed to lambda statement
var i; // lambda variable argument counter
lambda_statement += 'function';
lambda_expression = car(cdr(cdr(lexp)));
debugger;
if (lambda_args === undefined) { // passed lexp w/o passed in values per arg
lambda_expression = car(cdr(lexp));
lambda_var_args = car(lexp);
if ((car(lambda_var_args) === null) && (lambda_var_args.length === 1)) {
lambda_statement += "()";
} else {
lambda_statement += "(" + list_arguments(lambda_var_args) + ")";
}
lambda_statement += "{ return " + ast_to_js(lambda_expression, env) + '};';
return lambda_statement;
} else { // lambda is passed in arguments
lambda_expression = car(cdr(cdr(lexp)));
lambda_var_args = car(cdr(lexp));
lambda_statement += "(" + list_arguments(lambda_var_args) + ")";
lambda_statement += "{ return " + ast_to_js(lambda_expression, env) + "}(" + list_arguments(lambda_args) + ");";
return lambda_statement;
}
}
function is_within_env(arg, env) { // WARNING, MAY FAIL; needs refactor where called
return (bindings[arg] || env[arg]);
}
function list_arguments() {
// given an ast, output the values joined with ','. exluding null, which should be
// the last element of the ast.
var args_with_commas;
var arg_list = arguments[0];
if (arg_list[(arg_list.length - 1)] === null) {
arg_list.pop();// remove null
if (arg_list.length === 1) {
return arg_list[0];
} else {
args_with_commas = arg_list.join(', ');
}
}
return args_with_commas;
}
function translate_if(cdr_if, env) {
var conditional = car(cdr_if);
var expression = '';
var fexp = car(cdr(cdr(cdr_if)));
var texp = car(cdr(cdr_if));
expression += 'function () { if (' + ast_to_js(conditional, env) + ') { return ' + ast_to_js(texp, env) + '; }';
expression += ' else { return ' + ast_to_js(fexp, env) + '; }}()';
return expression;
}
function define(cdr_define, env) {
// passed the cdr of the define s-expression and the environment
var expression = '';
var procedure_args;
var procedure_expr;
var procedure_name;
// variable and expression/value or (function arguments) expression
if (predicates.is_array(car(cdr_define))) {
// we are defining a procedure that takes args
procedure_name = car(car(cdr_define));
procedure_args = cdr(car(cdr_define));
procedure_expr = car(cdr(cdr_define));
expression += 'var ' + procedure_name + ' = ';
expression += 'function ' +'(' + list_arguments(procedure_args) + ') {';
env[procedure_name] = 'tmp';
expression += 'return ' + ast_to_js(procedure_expr, env) + ';';
expression += '}';
add_binding_procedure(procedure_name, env);
return expression + ';';
} else if (predicates.is_string(car(cdr_define))) {
// we are defining something that accepts zero arguments
procedure_name = car((cdr_define));
procedure_expr = cdr(cdr_define);
expression += 'var ' + procedure_name + ' = ';
if (is_within_env(car(car(procedure_expr)), env)) { // if car expression is in env, pass procedure to ast_to_js
expression += ast_to_js(car(procedure_expr), env);
} else { // otherwise a var
expression += car(procedure_expr);
}
add_binding_var(procedure_name, ast_to_js(procedure_expr, env), env);
return expression + ';';
}
return '';
};
function translate_cons(cdr_cons) {
var first = car(cdr_cons);
var first_checked; // check quote status
var second = car(cdr(cdr_cons));
var second_checked; // check quote status
var result;
if (predicates.is_quoted(first)) { // eval each argument, unless quoted
if (predicates.is_array(cdr(first))) {
first_checked = car(cdr(first));
} else {
first_checked = cdr(first);
}
} else {
first_checked = ast_to_js(first, {});
}
if (predicates.is_quoted(second)) {
if (predicates.is_array(cdr(second))) {
second_checked = car(cdr(second));
} else {
second_checked = cdr(second);
}
} else {
second_checked = ast_to_js(second, {});
}
if (predicates.is_array(second_checked)) {
result = cons(first_checked, second_checked);
return scheme_data_to_js(result); // if this is not to be evaled
} else {
// if this is not to be evaled
return scheme_data_to_js([first, second]); // a dotted pair
}
}
var bindings = {
'+': generate_math_operator("+"),
'-': generate_math_operator("-"),
'*': generate_math_operator("*"),
'/': generate_math_operator("/"),
'<': generate_compare('<'),
'>': generate_compare('>'),
'>=': generate_compare('>='),
'=': generate_compare('==='),
'<=': generate_compare('<='),
lambda: lambda,
'BACKQUOTE': expand_vars,
'let': translate_let,
define: define,
'if': translate_if,
cons: translate_cons // cons scheme to Javascript. cons() works on the AST but translate_cons is for returning scheme data
};
function add_binding_procedure(name, binding) {
// TODO: do not allow rebinding of builtins???
binding[name] = local_procedure(name);
}
function add_binding_var(name, value, binding) {
binding[name] = value;
}
function local_procedure(name) {
return function(args, env) {
// TODO: ast_to_js over each args???
var function_call = '';
var i = 0; // counter
var argument_stack = [];
function_call += name;
function_call += '(';
// check if an argument in an expression
for (var j = 0; j < args.length; j++) {
if (args[j] != null) {
argument_stack.push(ast_to_js(args[j], env));
}
}
function_call += argument_stack.join(',');
function_call += ');';
// function_call += '(';
// for (i; i<arguments.length; i++) {
// args.push(arguments[i]);
// }
// function_call += args.join(', ');
// function_call += ');';
return function_call;
};
}
function generate_math_operator(op) {
return function(args, env) {
assert.deepEqual(true, (args.length >= 3));
var first;
var i;
var last;
var statement = '';
var tmp;
first = args[0];
statement += ast_to_js(first, env);
for (i=1; i<args.length; i++) {
tmp = predicates.is_array(args[i]) ? ast_to_js(args[i], env) : args[i];
if (i === (args.length - 1)) {
if (predicates.is_null(tmp)) {
break;
} else if (predicates.is_array(tmp)) {
statement += (op + ast_to_js(last, env));
} else {
throw new Error(args[i] + ', last item in a list, is not an s-expression or null');
}
break;
} // not at last arg
// support variables that are dynamically loaded into `bindings`
if (env[tmp]) { // not working
statement += (op + tmp);
} else { // a number
statement += (op + tmp);
}
}
return '(' + statement + ')';
};
}
function generate_compare(op) {
return function (args, env) {
var first;
var i = 0;
var arg_length = args.length;
var second;
var statement = '';
assert.deepEqual(true, (args.length >= 2));
do {
first = predicates.is_array(args[i]) ? ast_to_js(args[i], env) : args[i];
second = predicates.is_array(args[i+1]) ? ast_to_js(args[i+1], env) : args[i+1];
if (i === arg_length - 2) {
if (predicates.is_null(second)) {
break;
} else if (predicates.is_array(first)) {
statement += (op + ast_to_js(first, env));
} else {
throw new Error(args[i] + ', last item in a list, is not an s-expression or null');
}
break;
}
statement += '(' + first + ' ' + op + ' ' + second + ')';
i++;
if (i < arg_length - 2) {
statement += ' && ';
}
} while (i < arg_length - 1)
return statement;
};
}
////////////////////////////////////////////////////////////////////////////////
function scheme_data_to_js(scheme_data) {
// return the unevaluated Scheme data as JavaScript data
// print identifiers as they are
// TODO: print quoted identifiers
// print Scheme strings as quoted strings
// recursively traverse tree and unquote strings for JavaScript representation after JSON.stringify is called
var i;
var output = '[';
var tmp = [];
for (i=0; i<scheme_data.length; i++) {
if (predicates.is_array(scheme_data[i])) {
tmp.push(scheme_data_to_js(scheme_data[i]));
} else if ( (i == (scheme_data.length - 1)) && predicates.is_null(scheme_data[i])) {
tmp.push('null');
} else {
if (predicates.is_quoted(scheme_data[i])) {
tmp.push(scheme_data[i]);
} else {
tmp.push(scheme_data[i].toString());
}
}
}
output += tmp.join(",");
output += "]";
return output;
// parse out the quotes unless the string is quoted. That is,
// if a string is quoted with one quote on each end, remove them because
// this string is not meant to be quoted- it is meant to be a symbol ( eg within an environment context )
};
function double_to_single_quoted(string) {
// TODO: check that the quote comes at the ends of the string and that the
// matching groups are the same
// replaces doubly quoted strings ( ie. '"\"string\""' becomes '"string"'
var quote_test = /(\'\")|(\"\')|(\"\")|(\'\')/g;
return string.replace(quote_test, '"');
}
function single_to_none(string) {
// TODO: check that the quote comes at the ends of the string and that the
// matching groups are the same
var quote_test = /(\')|(\")/g;
return string.replace(quote_test, '');
}
function expand_vars(node, env) {
// pass iterate over each node recursively and replace symbols with
// values from env
var i; // counter
var expanded_node = []; // the evaluated node
if (predicates.is_array(node)) {
if (predicates.is_comma_escaped(node)) { // is escaped s-exp or var
if (predicates.is_array(car(cdr(node)))) { // is expression?
return expand_vars(car(cdr(node)), env);
} else if (env.hasOwnProperty(car(cdr(node)))) { // symbol in env?
return env[car(cdr(node))];
} else {
expanded_node.push(car(cdr(node)));
}
} else { // not escaped, but still an array so iterate over and expand vars
for (i=0; i<node.length; i++) {
expanded_node.push(expand_vars(node[i], env));
}
return expanded_node;
}
} else if (env.hasOwnProperty(node)) { // symbol in env?
return env[node];
} else {
return node;
}
return expanded_node;
}
function schript(text) {
// given Scheme, output JavaScript
var i; // counter
var LOCAL_ENV = {}; // the local environment
var tokens = tokenize(text); // all tokens
var sexps = parser.parse(tokens); // Arrays s-exps as tokens
var JS = '';
for (i=0; i< sexps.length; i++) {
JS += ast_to_js(sexps[i], LOCAL_ENV) + '\n';
}
return JS;
}
exports.schript = schript;
exports.expand_vars = expand_vars;
exports.ast_to_js = ast_to_js;
////////////////////////////////////////////////////////////////////////////////
// var input = "(define (addall x y z) (+ x y z))(addall 1 2 3)";
// print(schript(input));