-
Notifications
You must be signed in to change notification settings - Fork 1
/
11_language.js
179 lines (153 loc) · 5.23 KB
/
11_language.js
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
// Project: A programming language has been made as a chapter in the book
// Exercises in the chapter include changes of some features in the project
// Changes are contained in 11_language.js file
function parseExpression(program) {
program = skipSpace(program);
var match, expr;
if (match = /^"([^"]*)"/.exec(program))
expr = {type: "value", value: match[1]};
else if (match = /^\d+\b/.exec(program))
expr = {type: "value", value: Number(match[0])};
else if (match = /^[^\s(),"]+/.exec(program))
expr = {type: "word", name: match[0]};
else
throw new SyntaxError("Unexpected syntax: " + program);
return parseApply(expr, program.slice(match[0].length));
}
function skipSpace(string) {
var skip = /^(\s|#.*)*/.exec(string);
return string.slice(skip[0].length);
}
function parseApply(expr, program) {
program = skipSpace(program);
if (program[0] != "(")
return {expr: expr, rest: program};
program = skipSpace(program.slice(1));
expr = {type: "apply", operator: expr, args: []};
while (program[0] != ")") {
var arg = parseExpression(program);
expr.args.push(arg.expr);
program = skipSpace(arg.rest);
if (program[0] == ",")
program = skipSpace(program.slice(1));
else if (program[0] != ")")
throw new SyntaxError("Expected ',' or ')'");
}
return parseApply(expr, program.slice(1));
}
function parse(program) {
var result = parseExpression(program);
if (skipSpace(result.rest).length > 0)
throw new SyntaxError("Unexpected text after program");
return result.expr;
}
// operator: {type: "word", name: "+"},
// args: [{type: "word", name: "a"},
// {type: "value", value: 10}]}
function evaluate(expr, env) {
switch(expr.type) {
case "value":
return expr.value;
case "word":
if (expr.name in env)
return env[expr.name];
else
throw new ReferenceError("Undefined variable: " +
expr.name);
case "apply":
if (expr.operator.type == "word" &&
expr.operator.name in specialForms)
return specialForms[expr.operator.name](expr.args,
env);
var op = evaluate(expr.operator, env);
if (typeof op != "function")
throw new TypeError("Applying a non-function.");
return op.apply(null, expr.args.map(function(arg) {
return evaluate(arg, env);
}));
}
}
var specialForms = Object.create(null);
specialForms["if"] = function(args, env) {
if (args.length != 3)
throw new SyntaxError("Bad number of args to if");
if (evaluate(args[0], env) !== false)
return evaluate(args[1], env);
else
return evaluate(args[2], env);
};
specialForms["while"] = function(args, env) {
if (args.length != 2)
throw new SyntaxError("Bad number of args to while");
while (evaluate(args[0], env) !== false)
evaluate(args[1], env);
// Since undefined does not exist in Egg, we return false,
// for lack of a meaningful result.
return false;
};
specialForms["do"] = function(args, env) {
var value = false;
args.forEach(function(arg) {
value = evaluate(arg, env);
});
return value;
};
specialForms["define"] = function(args, env) {
if (args.length != 2 || args[0].type != "word")
throw new SyntaxError("Bad use of define");
var value = evaluate(args[1], env);
env[args[0].name] = value;
return value;
};
var topEnv = Object.create(null);
topEnv["true"] = true;
topEnv["false"] = false;
["+", "-", "*", "/", "==", "<", ">"].forEach(function(op) {
topEnv[op] = new Function("a, b", "return a " + op + " b;");
});
topEnv["print"] = function(value) {
console.log(value);
return value;
};
function run() {
var env = Object.create(topEnv);
var program = Array.prototype.slice
.call(arguments, 0).join("\n");
return evaluate(parse(program), env);
}
specialForms["fun"] = function(args, env) {
if (!args.length)
throw new SyntaxError("Functions need a body");
function name(expr) {
if (expr.type != "word")
throw new SyntaxError("Arg names must be words");
return expr.name;
}
var argNames = args.slice(0, args.length - 1).map(name);
var body = args[args.length - 1];
return function() {
if (arguments.length != argNames.length)
throw new TypeError("Wrong number of arguments");
var localEnv = Object.create(env);
for (var i = 0; i < arguments.length; i++)
localEnv[argNames[i]] = arguments[i];
return evaluate(body, localEnv);
};
};
topEnv["array"] = function () { return Array.prototype.slice.call(arguments, 0) };
topEnv["length"] = function (array) { return array.length };
topEnv["element"] = function(array, i) {return array[i] };
// specialForms["set"] made with help of the solution to the exercise
specialForms["set"] = function(args, env) {
if (args.length != 2 || args[0].type != "word")
throw new SyntaxError("Bad use of set");
var value = evaluate(args[1], env);
var varName = args[0].name;
for (var scope = env; scope; scope = Object.getPrototypeOf(scope)) {
if (Object.prototype.hasOwnProperty.call(scope, varName)) {
scope[varName] = value;
return value;
}
}
throw new ReferenceError("Variable must be defined to be changed, unknown var: " +varName);
};