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interpreter.js
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interpreter.js
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/*
Interpreter
Executes abstract syntax tree.
*/
;(function(exports) {
var Isla, _, multimethod;
if(typeof module !== 'undefined' && module.exports) { // node
_ = require("Underscore");
multimethod = require('multimethod');
Isla = {};
Isla.Utils = require('./utils').Utils;
Isla.Library = require('./library').Library;
Isla.Parser = require('./parser').Parser;
} else { // browser
_ = window._;
multimethod = window.multimethod;
Isla = window.Isla;
}
exports.Interpreter = {};
// takes raw Isla code, parses then interprets
exports.Interpreter.interpret = function(code, env) {
return interpretAst(Isla.Parser.parse(code), env);
};
var interpretAst = multimethod()
.dispatch(function(ast, env) {
return ast.tag;
})
.when("root", function(ast, env) {
if(env === undefined) {
env = Isla.Library.getInitialEnv();
}
return runSequence(ast.c, env);
})
.when("block", function(ast, env) {
return runSequence(ast.c, env);
})
.when("expression", function(ast, env) {
return interpretAst(ast.c[0], env);
})
.when("value_assignment", function(ast, env) {
var node = Isla.Parser.extract(ast, "value_assignment");
var assignee = node[0];
var valueNode = interpretAst(node[2], env);
var value = assignmentValue(valueNode);
var env = assign(env, assignee, value);
return rmRet(env);
})
.when("type_assignment", function(ast, env) {
var node = Isla.Parser.extract(ast, "type_assignment");
var assignee = node[0];
var typeIdentifier = interpretAst(node[2], env);
var value = instantiateType(typeIdentifier, env.ctx);
var env = assign(env, assignee, value);
return rmRet(env);
})
.when("list_assignment", function(ast, env) {
var node = Isla.Parser.extract(ast, "list_assignment");
var assignee = node[3];
var currentListEval = evaluateValue(Isla.Parser.extract(assignee,
"assignee", 0),
env);
var operation = Isla.Parser.extract(node, 0, "list_operation", 0).tag;
var itemEval = interpretAst(Isla.Parser.extract(node, 1), env);
var item = assignmentValue(itemEval);
var list = currentListEval.val;
list[operation](item);
var env = assign(env, assignee, currentListEval.val);
return rmRet(env);
})
.when("invocation", function(ast, env) {
var fn = resolve({
ref: interpretAst(Isla.Parser.extract(ast, "invocation", 0), env)
}, env).fn;
var param = resolve(interpretAst(Isla.Parser.extract(ast,
"invocation", 1),
env).val, env);
env.ret = fn(env, param);
return env;
})
.when("value", function(ast, env) {
var node = Isla.Parser.extract(ast, "value");
return evaluateValue(node[0], env);
})
.when("integer", function(ast, env) {
return Isla.Parser.extract(ast, "integer", 0);
})
.when("string", function(ast, env) {
return Isla.Parser.extract(ast, "string", 0);
})
.when("identifier", function(ast, env) {
return Isla.Parser.extract(ast, "identifier", 0);
})
.default(function(ast, env) {
throw { message:"You've forgotten a tag type." };
});
var evaluateValue = multimethod()
.dispatch(function(node, env) {
return node.tag;
})
.when("literal", function(node, env) {
return { val: interpretAst(node.c[0], env) };
})
.when("variable", function(node, env) {
return evaluateValue(node.c[0], env);
})
.when("scalar", function(node, env) {
var identifier = interpretAst(node.c[0], env);
var val = env.ctx[identifier];
if (val === undefined) {
nonExistentError([identifier]);
} else {
return { ref: identifier, val: val };
}
})
.when("object", function(node, env) {
var objNode = Isla.Parser.extract(node, "object");
checkIdentifierParts(objNode, env);
var parts = identifierParts(objNode, env);
var val = env.ctx;
for (var i = 0; i < objNode.length; i++) {
var id = Isla.Parser.extract(objNode, i, "identifier", 0);
val = val[canonical(id, env)];
}
return { ref: parts, val: val };
});
var nonExistentError = function(identifier) {
throw { message:"I have not heard of " + identifier.join(" ") + "." };
};
var checkIdentifierParts = function(objNode, env) {
var parts = identifierParts(objNode, env);
var val = env.ctx;
for (var i = 0; i < parts.length; i++) {
if (val === undefined) {
nonExistentError(parts.slice(0, i));
} else {
val = val[canonical(Isla.Parser.extract(objNode, i, "identifier", 0), env)];
}
}
};
var identifierParts = function(objNode, env) {
var parts = [];
for (var i = 0; i < objNode.length; i++) {
parts.push(Isla.Parser.extract(objNode, i, "identifier", 0));
}
return parts;
};
var assign = multimethod()
.dispatch(function(__, assigneeNode) {
return assigneeNode.c[0].tag;
})
.when("scalar", function(env, assigneeNode, value) {
var identifier = Isla.Parser.extract(assigneeNode, "assignee", 0,
"scalar", 0, "identifier", 0);
env.ctx[identifier] = value;
return env;
})
.when("object", function(env, assigneeNode, value) {
var objNode = Isla.Parser.extract(assigneeNode, "assignee", 0, "object");
checkIdentifierParts(objNode, env);
var slot = env.ctx;
for (var i = 0; i < objNode.length - 1; i++) {
var id = canonical(Isla.Parser.extract(objNode, i, "identifier", 0), env);
slot = slot[id];
}
slot[Isla.Parser.extract(objNode, i, "identifier", 0)] = value;
return env;
});
// returns appropriate value for valueNode being assigned
// actual value for primitives, refs
var assignmentValue = multimethod()
.dispatch(function(valueNode) {
return typeof(valueNode.val);
})
.when("string", function(valueNode) {
return valueNode.val;
})
.when("number", function(valueNode) {
return valueNode.val;
})
.default(function(valueNode) {
return valueNode.ref === undefined ? valueNode.val :
{ ref: valueNode.ref };
});
var resolve = multimethod()
.dispatch(function(thing) {
if (thing == null) {
return thing;
} else if(thing._meta && thing._meta.type === "list") {
return "list";
} else if(Isla.Utils.type(thing) === "Object") {
return thing.ref === undefined ? "object" : "ref";
}
})
.when("ref", function(thing, env) {
return resolve(env.ctx[thing.ref], env);
})
.when("object", function(thing, env) {
for(var i in thing) {
if(i !== "_meta") {
thing[i] = resolve(thing[i], env);
}
}
return thing;
})
.when("list", function(thing, env) {
var items = thing.items();
var resolvedList = new Isla.Library.List();
for(var i = 0; i < items.length; i++) {
resolvedList.add(resolve(items[i], env));
}
return resolvedList;
})
.default(function(thing) {
return thing;
});
var canonical = function(identifier, env) {
var next = env.ctx[identifier];
if (next === undefined) { // got scalar - just return id
return identifier;
} else if (next.ref !== undefined) { // keep going to find canon
return canonical(next.ref, env);
} else { // got value - return id
return identifier;
}
};
var runSequence = function(nodes, env) {
if(nodes.length === 0) {
return env;
}
else {
return runSequence(_.rest(nodes), interpretAst(_.first(nodes),
rmRet(env)));
}
}
var rmRet = function(env) {
env.ret = null;
return env;
}
// makes a new Isla object of the passed type
var instantiateType = function(type, ctx) {
var typeFn = ctx._types[type];
if(typeFn === undefined) {
typeFn = ctx._types.generic;
}
var obj = typeFn();
obj._meta = { type:type };
return obj;
};
exports.Interpreter.instantiateType = instantiateType;
exports.Interpreter.resolve = resolve;
exports.Interpreter.evaluateValue = evaluateValue;
exports.Interpreter.interpretAst = interpretAst;
})(typeof exports === 'undefined' ? this.Isla : exports);