JLambda/representation.js

var errors = require("./errors.js");
var _ = require("underscore");

var Expression = {
  display :
    function() {
      return this.exprType + " " + this.val;
    },
  type :
    function () {
      return this.exprType;
    },
  linenum : 0,
  charnum : 0
};

var TypeExpression = {
  unify :
    function (t) {
      if (this.expr === t.expr) {
        return t.expr;
      }
      else {
        console.log("Could not unify " + this.expr + " with " + t.expr);
      }
    },
  isTypeExpr : true,
  linenum : 0,
  charnum : 0
};

function isTypeExpr(x) {
  return x.isTypeExpr !== undefined;
}

function isIrregularTypeOp(x) {
  return (x === "->");
}

function flattenTypeDecl(stx) {
  if (isTypeExpr(stx)) {
    return true;
  }
  if (stx.exprType === "Application") {
    /* it might be a type application so recursively check it */
    if (stx.p !== undefined) {
      return  _.flatten([flattenTypeDecl(stx.p), flattenTypeDecl(stx.func)]);
    }
    else {
      return _.flatten([flattenTypeDecl(stx.func)]);
    }
  }
  if (stx.exprType === "Name") {
    /*
     * Either it is a type operator
     * or we assume it is a type variable
     * since it was not capitalized
     */
    return true;
  }
  return {
    failed : true,
    stx : stx
  };
}


function isTypeExprRec(stx) {
  var flattened = flattenTypeDecl(stx);
  for(var i = 0; i < flattened.length; i++) {
    if (flattened[i].failed !== undefined &&
        flattened[i].failed) {
          return flattened[i];
        }
  }
  return true;
}

function App(func, p) {
  this.func = func;
  this.exprType = "Application";
  if (p)
    this.p = p;
  return this;
}

function Closure(bound_vars, free_vars, body, env) {
  this.bound_vars = bound_vars;
  this.free_vars = free_vars;
  this.body = body;
  this.env = env;
  this.exprType = "Closure";
  return this;
}

function LetExp(pairs, body) {
  if (!pairs.every(function(x) {
    return (x.exprType === "Definition" ||
            x.exprType === "FunctionDefinition");
  })) {
    throw errors.JInternalError(
      "let can only be used to bind things to names or functions"
      );
  }
  this.exprType = "Let";
  this.val = [pairs, body];
  this.pairs = pairs;
  this.body = body;
  return this;
}
LetExp.prototype = Expression;

function UnaryOp(op, v) {
  this.exprType = "Unary";
  this.val = v;
  this.op = op;
  return this;
}
UnaryOp.prototype = Expression;

function IntT(v) {
  this.exprType = "Integer";
  this.val = parseInt(v, 10);
  return this;
}
IntT.prototype = Expression;

function FloatT(v) {
  this.exprType = "Float";
  this.val = parseFloat(v, 10);
  return this;
}

FloatT.prototype = Expression;

function StrT(v) {
  this.exprType = "String";
  this.val = v;
  return this;
}

StrT.prototype = Expression;

function BoolT(b) {
  if (b === "true") {
    this.val = true;
  }
  else {
    this.val = false;
  }
  this.exprType = "Bool";
  return this;
}

BoolT.prototype = Expression;

function ListT(xs) {
  this.xs = xs;
  this.val = xs;
  this.exprType = "List";
  return this;
}

ListT.prototype = Expression;

function Nil() {
  this.exprType = "Nil";
  return this;
}

Nil.prototype = Expression;


function FuncT(p, body) {
  this.p = p;
  this.body = body;
  this.val = [p, body];
  this.exprType = "Function";
  return this;
}

FuncT.prototype = Expression;

//Wrapper for function objects
function OpT(operator) {
  this.op = operator;
  this.val = this.op;
  this.exprType = "Function";
  return this;
}

OpT.prototype = Expression;

// Applications separate from other types
function App(func, p) {
  this.func = func;
  this.exprType = "Application";
  if (p)
    this.p = p;
  return this;
}

App.prototype = Expression;

// Names are not types
function Name(identifier) {
  this.ident = identifier;
  this.val = this.ident;
  this.exprType = "Name";
  return this;
}

Name.prototype = Expression;

function Def(ident, exp) {
  this.ident = ident;
  this.val = exp;
  this.exprType = "Definition";
  return this;
}

Def.prototype = Expression;

function DefFunc(ident, params, body) {
  this.ident = ident;
  this.val = this.ident;
  this.params = params;
  this.body = body;
  this.exprType = "FunctionDefinition";
  return this;
}

DefFunc.prototype = Expression;

function If(condition, thenexp, elseexp) {
  this.condition = condition;
  this.thenexp = thenexp;
  this.elseexp = elseexp;
  this.exprType = "If";
  return this;
}

If.prototype = Expression;

function TypeVar(name) {
  this.exprtype = "TypeVar";
  this.name = name;
  this.exprType = "TypeVar";
  return this;
}

TypeVar.prototype = TypeExpression;

function TypeOp(name) {
  this.name = name;
  this.val = name;
  this.exprType = "TypeOperator";
  return this;
}

TypeOp.prototype = TypeExpression;

function isTypeExpr(expr) {
  if (!expr.exprType) {
    throw errors.JInternalError(expr);
  }
  return ((expr.exprType === "TypeOperator") ||
          (expr.exprType === "TypeVar") ||
          (expr.exprType === "TypeDeclaration"));
}

function TypeDecl(expression, type) {
  if (isTypeExprRec(expression) &&
      expression.exprType !== "Name") {
    throw errors.JSyntaxError(
      expression.linenum,
      expression.charnum,
      "Left-hand-side of type declaration must not be in the type language"
      );
  }
  if (isTypeExprRec(type).failed) {
    throw errors.JInternalError(
      "Right-hand-side of type declaration must be a type expression"
      );
  }
  this.expression = expression;
  this.type = type;
  this.exprType = "TypeDeclaration";
  return this;
}

TypeDecl.prototype = TypeExpression;

function DefType(lhs, rhs) {
  /* Both rhs and lhs are expected
   * to be fully desugared already
   */
  if (isTypeExprRec(rhs).failed ||
      !isTypeExpr(lhs)) {
        throw errors.JSyntaxError(
          rhs.linenum,
          rhs.charnum,
          "Illegal type definition, both sides must be valid type expressions");
      }
  this.rhs = rhs;
  this.lhs = lhs;
  this.exprType = "TypeDefinition";
  return this;
}

DefType.prototype = Expression;

function checkName(exp) {
  if (exp.exprType !== "Name") {
    throw errors.JSyntaxError(
      exp.linenum,
      exp.charnum,
      "Expected a type variable (an identifier starting with a lowercase character), got " + exp.val);
  }
}

function DataType(name, params, type) {
  /* Params is a list of type variables
   * type is a type expression
   */
  if (name.exprType !== "TypeOperator") {
    throw errors.JSyntaxError(
      name.linenum,
      name.charnum,
      "First element in a data type definition must be its name " +
      "which is a type operator");
  }
  _.each(params, checkName);
  if (isTypeExprRec(type).failed) {
    throw errors.JSyntaxError(
      type.linenum,
      type.charnum,
      "Body of a type definition must be a valid type expression");
  }
  this.name = name;
  this.params = params;
  this.type = type;
  this.exprType = "TypeFuncDefinition";
  return this;
}


//Applies the function ``name'' to the list of parameters
function makeApp(name, parameters) {
  if (parameters) {
    return parameters.slice(1).reduce(function(f, ident) {
      return new App(f, ident);
    }, new App(name, parameters[0]));
  }
  else {
    return new App(name);
  }
}

function makeGensym() {
  var n = 0;
  return function() {
    var x = "G"+n;
    n = n + 1;
    return x;
  };
}

var gensym = makeGensym();

OPInfo = {
          "::" : [2, "Left"],
          "," : [1, "Left"],
          "->" : [1, "Right"]
         };

module.exports =
   {
     IntT   : IntT,
     FloatT : FloatT,
     StrT   : StrT,
     BoolT  : BoolT,
     ListT  : ListT,
     FuncT  : FuncT,
     App    : App,
     Name   : Name,
     Def    : Def,
     OpT   : OpT,
     OPInfo : OPInfo,
     makeApp : makeApp,
     If : If,
     DefFunc : DefFunc,
     UnaryOp : UnaryOp,
     Nil : Nil,
     LetExp : LetExp,
     gensym : gensym,
     TypeVar : TypeVar,
     TypeOp : TypeOp,
     TypeDecl : TypeDecl,
     Closure : Closure,
     isTypeExpr : isTypeExprRec,
     DefType : DefType,
     DataType : DataType
   };