js/step8_macros.js

   1 if (typeof module !== 'undefined') {
   2     var types = require('./types');
   3     var readline = require('./node_readline');
   4     var reader = require('./reader');
   5     var printer = require('./printer');
   6     var Env = require('./env').Env;
   7     var core = require('./core');
   8 }
   9
  10 // read
  11 function READ(str) {
  12     return reader.read_str(str);
  13 }
  14
  15 // eval
  16 function is_pair(x) {
  17     return types._sequential_Q(x) && x.length > 0;
  18 }
  19
  20 function quasiquote(ast) {
  21     if (!is_pair(ast)) {
  22         return [types._symbol("quote"), ast];
  23     } else if (types._symbol_Q(ast[0]) && ast[0].value === 'unquote') {
  24         return ast[1];
  25     } else if (is_pair(ast[0]) && ast[0][0].value === 'splice-unquote') {
  26         return [types._symbol("concat"),
  27                 ast[0][1],
  28                 quasiquote(ast.slice(1))];
  29     } else {
  30         return [types._symbol("cons"),
  31                 quasiquote(ast[0]),
  32                 quasiquote(ast.slice(1))];
  33     }
  34 }
  35
  36 function is_macro_call(ast, env) {
  37     return types._list_Q(ast) &&
  38            types._symbol_Q(ast[0]) &&
  39            env.find(ast[0]) &&
  40            env.get(ast[0])._ismacro_;
  41 }
  42
  43 function macroexpand(ast, env) {
  44     while (is_macro_call(ast, env)) {
  45         var mac = env.get(ast[0]);
  46         ast = mac.apply(mac, ast.slice(1));
  47     }
  48     return ast;
  49 }
  50
  51 function eval_ast(ast, env) {
  52     if (types._symbol_Q(ast)) {
  53         return env.get(ast);
  54     } else if (types._list_Q(ast)) {
  55         return ast.map(function(a) { return EVAL(a, env); });
  56     } else if (types._vector_Q(ast)) {
  57         var v = ast.map(function(a) { return EVAL(a, env); });
  58         v.__isvector__ = true;
  59         return v;
  60     } else if (types._hash_map_Q(ast)) {
  61         var new_hm = {};
  62         for (k in ast) {
  63             new_hm[EVAL(k, env)] = EVAL(ast[k], env);
  64         }
  65         return new_hm;
  66     } else {
  67         return ast;
  68     }
  69 }
  70
  71 function _EVAL(ast, env) {
  72     while (true) {
  73
  74     //printer.println("EVAL:", printer._pr_str(ast, true));
  75     if (!types._list_Q(ast)) {
  76         return eval_ast(ast, env);
  77     }
  78
  79     // apply list
  80     ast = macroexpand(ast, env);
  81     if (!types._list_Q(ast)) {
  82         return eval_ast(ast, env);
  83     }
  84     if (ast.length === 0) {
  85         return ast;
  86     }
  87
  88     var a0 = ast[0], a1 = ast[1], a2 = ast[2], a3 = ast[3];
  89     switch (a0.value) {
  90     case "def!":
  91         var res = EVAL(a2, env);
  92         return env.set(a1, res);
  93     case "let*":
  94         var let_env = new Env(env);
  95         for (var i=0; i < a1.length; i+=2) {
  96             let_env.set(a1[i], EVAL(a1[i+1], let_env));
  97         }
  98         ast = a2;
  99         env = let_env;
 100         break;
 101     case "quote":
 102         return a1;
 103     case "quasiquote":
 104         ast = quasiquote(a1);
 105         break;
 106     case 'defmacro!':
 107         var func = types._clone(EVAL(a2, env));
 108         func._ismacro_ = true;
 109         return env.set(a1, func);
 110     case 'macroexpand':
 111         return macroexpand(a1, env);
 112     case "do":
 113         eval_ast(ast.slice(1, -1), env);
 114         ast = ast[ast.length-1];
 115         break;
 116     case "if":
 117         var cond = EVAL(a1, env);
 118         if (cond === null || cond === false) {
 119             ast = (typeof a3 !== "undefined") ? a3 : null;
 120         } else {
 121             ast = a2;
 122         }
 123         break;
 124     case "fn*":
 125         return types._function(EVAL, Env, a2, env, a1);
 126     default:
 127         var el = eval_ast(ast, env), f = el[0];
 128         if (f.__ast__) {
 129             ast = f.__ast__;
 130             env = f.__gen_env__(el.slice(1));
 131         } else {
 132             return f.apply(f, el.slice(1));
 133         }
 134     }
 135
 136     }
 137 }
 138
 139 function EVAL(ast, env) {
 140     var result = _EVAL(ast, env);
 141     return (typeof result !== "undefined") ? result : null;
 142 }
 143
 144 // print
 145 function PRINT(exp) {
 146     return printer._pr_str(exp, true);
 147 }
 148
 149 // repl
 150 var repl_env = new Env();
 151 var rep = function(str) { return PRINT(EVAL(READ(str), repl_env)); };
 152
 153 // core.js: defined using javascript
 154 for (var n in core.ns) { repl_env.set(types._symbol(n), core.ns[n]); }
 155 repl_env.set(types._symbol('eval'), function(ast) {
 156     return EVAL(ast, repl_env); });
 157 repl_env.set(types._symbol('*ARGV*'), []);
 158
 159 // core.mal: defined using the language itself
 160 rep("(def! not (fn* (a) (if a false true)))");
 161 rep("(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \"\nnil)\")))))");
 162 rep("(defmacro! cond (fn* (& xs) (if (> (count xs) 0) (list 'if (first xs) (if (> (count xs) 1) (nth xs 1) (throw \"odd number of forms to cond\")) (cons 'cond (rest (rest xs)))))))");
 163
 164 if (typeof process !== 'undefined' && process.argv.length > 2) {
 165     repl_env.set(types._symbol('*ARGV*'), process.argv.slice(3));
 166     rep('(load-file "' + process.argv[2] + '")');
 167     process.exit(0);
 168 }
 169
 170 // repl loop
 171 if (typeof require !== 'undefined' && require.main === module) {
 172     // Synchronous node.js commandline mode
 173     while (true) {
 174         var line = readline.readline("user> ");
 175         if (line === null) { break; }
 176         try {
 177             if (line) { printer.println(rep(line)); }
 178         } catch (exc) {
 179             if (exc instanceof reader.BlankException) { continue }
 180             if (exc instanceof Error) { console.warn(exc.stack) }
 181             else { console.warn("Error: " + printer._pr_str(exc, true)) }
 182         }
 183     }
 184 }