"""
  This module parses source code into an abstract syntax tree (AST)
"""

from .symboltable import SymbolTable
from .nodes import *
from ...core.errors import CompilerException, Error
from .builtin import *
#from . import assembler
from .lexer import tokenize

class KsParser:
   def __init__(self, source):
      """ provide the parser with the tokens iterator from the lexer. """
      self.tokens = tokenize(source) # Lexical stage
      self.NextToken()
      self.errorlist = []

   def Error(self, msg):
     raise CompilerException(msg, self.token.row, self.token.col)

   # Lexer helpers:
   def Consume(self, typ=''):
     if self.token.typ == typ or typ == '':
       v = self.token.val
       self.NextToken()
       return v
     else:
       self.Error('Excected: "{0}", got "{1}"'.format(typ, self.token.val))

   def hasConsumed(self, typ):
      if self.token.typ == typ:
         self.Consume(typ)
         return True
      return False
     
   def NextToken(self):
     self.token = self.tokens.__next__()
     # TODO: store filename in location?
     self.location = (self.token.row, self.token.col)

   # Helpers to find location of the error in the code:
   def setLocation(self, obj, location):
      obj.location = location
      return obj
   def getLocation(self):
      return self.location

   """
     Recursive descent parser functions:
        A set of mutual recursive functions.
        Starting symbol is the Module.
   """
   def parseModule(self):
       """ Top level parsing routine """
       self.imports = []
       loc = self.getLocation()
       self.Consume('module')
       modname = self.Consume('ID')
       self.Consume(';')
       mod = Module(modname)

       # Construct a symbol table for this program
       mod.symtable = SymbolTable()
       # Add built in types and functions:
       for x in [real, integer, boolean, char, chr_func]:
          mod.symtable.addSymbol(x)

       self.cst = mod.symtable
       self.parseImportList()

       self.parseDeclarationSequence()
       # Procedures only allowed in this scope
       self.parseProcedureDeclarations()

       if self.hasConsumed('begin'):
          mod.initcode = self.parseStatementSequence()
       else:
          mod.initcode = EmptyStatement()

       self.Consume('end')
       endname = self.Consume('ID')
       if endname != modname:
          self.Error('end denoter must be module name')
       self.Consume('.')

       mod.imports = self.imports
       return self.setLocation(mod, loc)

   # Import part
   def parseImportList(self):
      if self.hasConsumed('import'):
         self.parseImport()
         while self.hasConsumed(','):
            self.parseImport()
         self.Consume(';')

   def parseImport(self):
      loc = self.getLocation()
      modname = self.Consume('ID')
      #mod = loadModule(modname)
      self.setLocation(mod, loc)
      self.cst.addSymbol(mod)

   # Helper to parse an identifier defenitions
   def parseIdentDef(self):
      loc = self.getLocation()
      name = self.Consume('ID')
      ispublic = self.hasConsumed('*')
      # Make a node of this thing:
      i = Id(name)
      i.ispublic = ispublic
      return self.setLocation(i, loc)

   def parseIdentList(self):
      ids = [ self.parseIdentDef() ]
      while self.hasConsumed(','):
         ids.append( self.parseIdentDef() )
      return ids

   def parseQualIdent(self):
      """ Parse a qualified identifier """
      name = self.Consume('ID')
      if self.cst.has(Module, name):
         modname = name
         mod = self.cst.get(Module, modname)
         self.Consume('.')
         name = self.Consume('ID')
         # Try to find existing imported symbol:
         for imp in self.imports:
            if imp.modname == modname and imp.name == name:
               return imp
         # Try to find the symbol in the modules exports:
         for sym in mod.exports:
            if sym.name == name:
               impsym = ImportedSymbol(modname, name)
               impsym.typ = sym.typ
               impsym.signature = mod.signature
               self.imports.append(impsym)
               return impsym
         self.Error("Cannot find symbol {0}".format(name))
      else:
         return self.cst.getSymbol(name)

   # Helper to parse a designator
   def parseDesignator(self):
      """ A designator designates an object.
           The base location in memory is denoted by the qualified identifier
           The actual address depends on the selector.
      """
      loc = self.getLocation()
      obj = self.parseQualIdent()
      typ = obj.typ
      selectors = []
      while self.token.typ in ['.', '[', '^']:
         if self.hasConsumed('.'):
            field = self.Consume('ID')
            if typ is PointerType:
               selectors.append(Deref())
               typ = typ.pointedType
            if not type(typ) is RecordType:
               self.Error("field reference, type not record but {0}".format(typ))
            typ = typ.fields[field]
            selectors.append(Field(field))
         elif self.hasConsumed('['):
            indexes = self.parseExpressionList()
            self.Consume(']')
            for idx in indexes:
               if not type(typ) is ArrayType:
                  self.Error('Cannot index non array type')
               if not isType(idx.typ, integer):
                  self.Error('Only integer expressions can be used as an index')
               selectors.append(Index(idx, typ))
               typ = typ.elementType
         elif self.hasConsumed('^'):
            selectors.append(Deref())
            typ = typ.pointedType
      return self.setLocation(Designator(obj, selectors, typ), loc)

   # Declaration sequence
   def parseDeclarationSequence(self):
      """ 1. constants, 2. types, 3. variables """
      self.parseConstantDeclarations()
      self.parseTypeDeclarations()
      self.parseVariableDeclarations()

   # Constants
   def evalExpression(self, expr):
      if type(expr) is Binop:
         a = self.evalExpression(expr.a)
         b = self.evalExpression(expr.b)
         if expr.op == '+':
            return a + b
         elif expr.op == '-':
            return a - b
         elif expr.op == '*':
            return a * b
         elif expr.op == '/':
            return float(a) / float(b)
         elif expr.op == 'mod':
            return int(a % b)
         elif expr.op == 'div':
            return int(a / b)
         elif expr.op == 'or':
            return a or b
         elif expr.op == 'and':
            return a and b
         else:
            self.Error('Cannot evaluate expression with {0}'.format(expr.op))
      elif type(expr) is Constant:
         return expr.value
      elif type(expr) is Designator:
         if type(expr.obj) is Constant:
            return self.evalExpression(expr.obj)
         else:
            self.Error('Cannot evaluate designated object {0}'.format(expr.obj))
      elif type(expr) is Unop:
         a = self.evalExpression(expr.a)
         if expr.op == 'not':
            return not a
         elif expr.op == '-':
            return -a 
         else:
            self.Error('Unimplemented unary operation {0}'.format(expr.op))
      else:
         self.Error('Cannot evaluate expression {0}'.format(expr))

   def parseConstExpression(self):
      e = self.parseExpression()
      return self.evalExpression(e), e.typ

   def parseConstantDeclarations(self):
      """ Parse const part of a module """
      if self.hasConsumed('const'):
         while self.token.typ == 'ID':
            i = self.parseIdentDef()
            self.Consume('=')
            constvalue, typ = self.parseConstExpression()
            self.Consume(';')
            c = Constant(constvalue, typ, name=i.name, public=i.ispublic)
            self.setLocation(c, i.location)
            self.cst.addSymbol(c)
     
   # Type system
   def parseTypeDeclarations(self):
      if self.hasConsumed('type'):
         while self.token.typ == 'ID':
            typename, export = self.parseIdentDef()
            self.Consume('=')
            typ = self.parseStructuredType()
            self.Consume(';')
            t = DefinedType(typename, typ)
            self.cst.addSymbol(t)

   def parseType(self):
      if self.token.typ == 'ID':
         typename = self.Consume('ID')
         if self.cst.has(Type, typename):
            typ = self.cst.get(Type, typename)
            while type(typ) is DefinedType:
               typ = typ.typ
            return typ
         else:
            self.Error('Cannot find type {0}'.format(typename))
      else:
         return self.parseStructuredType()

   def parseStructuredType(self):
      if self.hasConsumed('array'):
         dimensions = []
         dimensions.append( self.parseConstExpression() )
         while self.hasConsumed(','):
             dimensions.append( self.parseConstExpression() )
         self.Consume('of')
         arr = self.parseType()
         for dimension, consttyp in reversed(dimensions):
            if not isType(consttyp, integer):
               self.Error('array dimension must be an integer type (not {0})'.format(consttyp))
            if dimension < 2:
               self.Error('array dimension must be bigger than 1 (not {0})'.format(dimension))
            arr = ArrayType(dimension, arr)
         return arr
      elif self.hasConsumed('record'):
         fields = {}
         while self.token.typ == 'ID':
            # parse a fieldlist:
            identifiers = self.parseIdentList()
            self.Consume(':')
            typ = self.parseType()
            self.Consume(';')
            for i in identifiers:
               if i.name in fields.keys():
                  self.Error('record field "{0}" multiple defined.'.format(i.name))
               fields[i.name] = typ
            # TODO store this in another way, symbol table?
         self.Consume('end')
         return RecordType(fields)
      elif self.hasConsumed('pointer'):
         self.Consume('to')
         typ = self.parseType()
         return PointerType(typ)
      elif self.hasConsumed('procedure'):
         parameters, returntype = self.parseFormalParameters()
         return ProcedureType(parameters, returntype)
      else:
         self.Error('Unknown structured type "{0}"'.format(self.token.val))

   # Variable declarations:
   def parseVariableDeclarations(self):
      if self.hasConsumed('var'):
         if self.token.typ == 'ID':
            while self.token.typ == 'ID':
               ids = self.parseIdentList()
               self.Consume(':')
               typename = self.parseType()
               self.Consume(';')
               for i in ids:
                  v = Variable(i.name, typename, public=i.ispublic)
                  self.setLocation(v, i.location)
                  self.cst.addSymbol(v)
         else:
            self.Error('Expected ID, got'+str(self.token))

   # Procedures
   def parseFPsection(self):
      if self.hasConsumed('const'):
         kind = 'const'
      elif self.hasConsumed('var'):
         kind = 'var'
      else:
         kind = 'value'
      names = [ self.Consume('ID') ]
      while self.hasConsumed(','):
         names.append( self.Consume('ID') )
      self.Consume(':')
      typ = self.parseType()
      parameters = [Parameter(kind, name, typ)
            for name in names]
      return parameters

   def parseFormalParameters(self):
      parameters = []
      self.Consume('(')
      if not self.hasConsumed(')'):
         parameters += self.parseFPsection()
         while self.hasConsumed(';'):
            parameters += self.parseFPsection()
         self.Consume(')')
      if self.hasConsumed(':'):
         returntype = self.parseQualIdent()
      else:
         returntype = void
      return ProcedureType(parameters, returntype)

   def parseProcedureDeclarations(self):
     procedures = []
     while self.token.typ == 'procedure':
       p = self.parseProcedureDeclaration()
       procedures.append(p)
       self.Consume(';')
     return procedures

   def parseProcedureDeclaration(self):
     loc = self.getLocation()
     self.Consume('procedure')
     i = self.parseIdentDef()
     procname = i.name
     proctyp = self.parseFormalParameters()
     procsymtable = SymbolTable(parent = self.cst)
     self.cst = procsymtable    # Switch symbol table:
     # Add parameters as variables to symbol table:
     for parameter in proctyp.parameters:
        vname = parameter.name
        vtyp = parameter.typ
        if parameter.kind == 'var':
           vtyp = PointerType(vtyp)
        variable = Variable(vname, vtyp, False)
        if parameter.kind == 'const':
           variable.isReadOnly = True
        variable.isParameter = True
        self.cst.addSymbol(variable)
     self.Consume(';')
     self.parseDeclarationSequence()
     # Mark all variables as local:
     for variable in self.cst.getAllLocal(Variable):
        variable.isLocal = True

     if self.hasConsumed('begin'):
        block = self.parseStatementSequence()
     if self.hasConsumed('return'):
        returnexpression = self.parseExpression()
     else:
        returnexpression = None

     if proctyp.returntype.isType(void):
        if not returnexpression is None:
           self.Error('Void procedure cannot return a value')
     else:
        if returnexpression is None:
           self.Error('Procedure must return a value')
        if not isType(returnexpression.typ, proctyp.returntype):
           self.Error('Returned type {0} does not match function return type {1}'.format(returnexpression.typ, proctyp.returntype))

     self.Consume('end')
     endname = self.Consume('ID')
     if endname != procname:
        self.Error('endname should match {0}'.format(name))
     self.cst = procsymtable.parent    # Switch back to parent symbol table
     proc = Procedure(procname, proctyp, block, procsymtable, returnexpression)
     self.setLocation(proc, loc)
     self.cst.addSymbol(proc)
     proc.public = i.ispublic
     return proc

   # Statements:
   def parseAssignment(self, lval):
      loc = self.getLocation()
      self.Consume(':=')
      rval = self.parseExpression()
      if isType(lval.typ, real) and isType(rval.typ, integer):
         rval = Unop(rval, 'INTTOREAL', real)
      if type(rval.typ) is NilType:
         if not type(lval.typ) is ProcedureType and not type(lval.typ) is PointerType:
            self.Error('Can assign nil only to pointers or procedure types, not {0}'.format(lval))
      elif not isType(lval.typ, rval.typ):
         self.Error('Type mismatch {0} != {1}'.format(lval.typ, rval.typ))
      return self.setLocation(Assignment(lval, rval), loc)

   def parseExpressionList(self):
      expressions = [ self.parseExpression() ]
      while self.hasConsumed(','):
         expressions.append( self.parseExpression() )
      return expressions

   def parseProcedureCall(self, procedure):
      self.Consume('(')
      if self.token.typ != ')':
         args = self.parseExpressionList()
      else:
         args = []
      self.Consume(')')
      parameters = procedure.typ.parameters
      if len(args) != len(parameters):
         self.Error("Procedure requires {0} arguments, {1} given".format(len(parameters), len(args)))
      for arg, param in zip(args, parameters):
         if not arg.typ.isType(param.typ):
            print(arg.typ, param.typ)
            self.Error('Mismatch in parameter')
      return ProcedureCall(procedure, args)

   def parseIfStatement(self):
     loc = self.getLocation()
     self.Consume('if')
     ifs = []
     condition = self.parseExpression()
     if not isType(condition.typ, boolean):
         self.Error('condition of if statement must be boolean')
     self.Consume('then')
     truestatement = self.parseStatementSequence()
     ifs.append( (condition, truestatement) )
     while self.hasConsumed('elsif'):
        condition = self.parseExpression()
        if not isType(condition.typ, boolean):
            self.Error('condition of if statement must be boolean')
        self.Consume('then')
        truestatement = self.parseStatementSequence()
        ifs.append( (condition, truestatement) )
     if self.hasConsumed('else'):
        statement = self.parseStatementSequence()
     else:
        statement = None
     self.Consume('end')
     for condition, truestatement in reversed(ifs):
         statement = IfStatement(condition, truestatement, statement)
     return self.setLocation(statement, loc)

   def parseCase(self):
      # TODO
      pass

   def parseCaseStatement(self):
      self.Consume('case')
      expr = self.parseExpression()
      self.Consume('of')
      self.parseCase()
      while self.hasConsumed('|'):
         self.parseCase()
      self.Consume('end')

   def parseWhileStatement(self):
      loc = self.getLocation()
      self.Consume('while')
      condition = self.parseExpression()
      self.Consume('do')
      statements = self.parseStatementSequence()
      if self.hasConsumed('elsif'):
         self.Error('elsif in while not yet implemented')
      self.Consume('end')
      return self.setLocation(WhileStatement(condition, statements), loc)

   def parseRepeatStatement(self):
      self.Consume('repeat')
      stmt = self.parseStatementSequence()
      self.Consume('until')
      cond = self.parseBoolExpression()

   def parseForStatement(self):
      loc = self.getLocation()
      self.Consume('for')
      variable = self.parseDesignator()
      if not variable.typ.isType(integer):
         self.Error('loop variable of for statement must have integer type')
      assert(variable.typ.isType(integer))
      self.Consume(':=')
      begin = self.parseExpression()
      if not begin.typ.isType(integer):
         self.Error('begin expression of a for statement must have integer type')
      self.Consume('to')
      end = self.parseExpression()
      if not end.typ.isType(integer):
         self.Error('end expression of a for statement must have integer type')
      if self.hasConsumed('by'):
         increment, typ = self.parseConstExpression()
         if not typ.isType(integer):
            self.Error('Increment must be integer')
      else:
         increment = 1
      assert(type(increment) is int)
      self.Consume('do')
      statements = self.parseStatementSequence()
      self.Consume('end')
      return self.setLocation(ForStatement(variable, begin, end, increment, statements), loc)

   def parseAsmcode(self):
      # TODO: move this to seperate file
      def parseOpcode():
         return self.Consume('ID')
      def parseOperand():
         if self.hasConsumed('['):
            memref = []
            memref.append(parseOperand())
            self.Consume(']')
            return memref
         else:
            if self.token.typ == 'NUMBER':
               return self.Consume('NUMBER')
            else:
               ID = self.Consume('ID')
               if self.cst.has(Variable, ID):
                  return self.cst.get(Variable, ID)
               else:
                  return ID
               
      def parseOperands(n):
         operands = []
         if n > 0:
            operands.append( parseOperand() )
            n = n - 1
            while n > 0:
               self.Consume(',')
               operands.append(parseOperand())
               n = n - 1
         return operands
      self.Consume('asm')
      asmcode = []
      while self.token.typ != 'end':
         opcode = parseOpcode()
         func, numargs = assembler.opcodes[opcode]
         operands = parseOperands(numargs)
         asmcode.append( (opcode, operands) )
         #print('opcode', opcode, operands)
      self.Consume('end')
      return AsmCode(asmcode)

   def parseStatement(self):
     try:
        # Determine statement type based on the pending token:
        if self.token.typ == 'if':
           return self.parseIfStatement()
        elif self.token.typ == 'case':
           return self.parseCaseStatement()
        elif self.token.typ == 'while':
          return self.parseWhileStatement()
        elif self.token.typ == 'repeat':
           return self.parseRepeatStatement()
        elif self.token.typ == 'for':
           return self.parseForStatement()
        elif self.token.typ == 'asm':
           return self.parseAsmcode()
        elif self.token.typ == 'ID':
           # Assignment or procedure call
           designator = self.parseDesignator()
           if self.token.typ == '(' and type(designator.typ) is ProcedureType:
              return self.parseProcedureCall(designator)
           elif self.token.typ == ':=':
              return self.parseAssignment(designator)
           else:
              self.Error('Unknown statement following designator: {0}'.format(self.token))
        else:
           # TODO: return empty statement??:
           return EmptyStatement()
           self.Error('Unknown statement {0}'.format(self.token))
     except CompilerException as e:
         print(e)
         self.errorlist.append( (e.row, e.col, e.msg))
         # Do error recovery by skipping all tokens until next ; or end
         while not (self.token.typ == ';' or self.token.typ == 'end'):
            self.Consume(self.token.typ)
         return EmptyStatement()

   def parseStatementSequence(self):
       """ Sequence of statements seperated by ';' """
       statements = [ self.parseStatement() ]
       while self.hasConsumed(';'):
         statements.append( self.parseStatement() )
       return StatementSequence( statements )

   # Parsing expressions:
   """
     grammar of expressions:
     expression       = SimpleExpression [ reloperator SimpleExpression ]
     reloperator      = '=' | '<=' | '>=' | '<>'
     Simpleexpression = [ '+' | '-' ] term { addoperator term }
     addoperator      = '+' | '-' | 'or'
     term             = factor { muloperator factor }
     muloperator      = '*' | '/' | 'div' | 'mod' | 'and'
     factor           = number | nil | true | false | "(" expression ")" | 
                        designator [ actualparameters ] | 'not' factor
   """
   def parseExpression(self):
      """ The connector between the boolean and expression domain """
      expr = self.parseSimpleExpression()
      if self.token.typ in ['>=','<=','<','>','<>','=']:
         relop = self.Consume()
         expr2 = self.parseSimpleExpression()
         # Automatic type convert to reals:
         if isType(expr.typ, real) and isType(expr2.typ, integer):
            expr2 = Unop(expr2, 'INTTOREAL', real)
         if isType(expr2.typ, real) and isType(expr.typ, integer):
            expr = Unop(expr, 'INTTOREAL', real)
         # Type check:
         if not isType(expr.typ, expr2.typ):
            self.Error('Type mismatch in relop')
         if isType(expr.typ, real) and relop in ['<>', '=']:
            self.Error('Cannot check real values for equality')

         expr = Relop(expr, relop, expr2, boolean)
      return expr

   # Parsing arithmatic expressions:
   def parseTerm(self):
       a = self.parseFactor()
       while self.token.typ in ['*', '/', 'mod', 'div', 'and']:
           loc = self.getLocation()
           op = self.Consume()
           b = self.parseTerm()
           # Type determination and checking:
           if op in ['mod', 'div']:
              if not isType(a.typ, integer):
                 self.Error('First operand should be integer, not {0}'.format(a.typ))
              if not isType(b.typ, integer):
                 self.Error('Second operand should be integer, not {0}'.format(b.typ))
              typ = integer
           elif op == '*':
              if isType(a.typ, integer) and isType(b.typ, integer):
                 typ = integer
              elif isType(a.typ, real) or isType(b.typ, real):
                 if isType(a.typ, integer):
                    # Automatic type cast
                    a = Unop(a, 'INTTOREAL', real)
                 if isType(b.typ, integer):
                    b = Unop(b, 'INTTOREAL', real)
                 if not isType(a.typ, real):
                    self.Error('first operand must be a real!')
                 if not isType(b.typ, real):
                    self.Error('second operand must be a real!')
                 typ = real
              else:
                 self.Error('Unknown operands for multiply: {0}, {1}'.format(a, b))
           elif op == '/':
              # Division always yields a real result, for integer division use div
              if isType(a.typ, integer):
                 # Automatic type cast
                 a = Unop(a, 'INTTOREAL', real)
              if isType(b.typ, integer):
                 b = Unop(b, 'INTTOREAL', real)
              if not isType(a.typ, real):
                 self.Error('first operand must be a real!')
              if not isType(b.typ, real):
                 self.Error('second operand must be a real!')
              typ = real
           elif op == 'and':
              if not isType(a.typ, boolean):
                 self.Error('First operand of and must be boolean')
              if not isType(b.typ, boolean):
                 self.Error('Second operand of and must be boolean')
              typ = boolean
           else:
              self.Error('Unknown operand {0}'.format(op))

           a = self.setLocation(Binop(a, op, b, typ), loc)
       return a

   def parseFactor(self):
      if self.hasConsumed('('):
         e = self.parseExpression()
         self.Consume(')')
         return e
      elif self.token.typ == 'NUMBER':
         loc = self.getLocation() 
         val = self.Consume('NUMBER')
         return self.setLocation(Constant(val, integer), loc)
      elif self.token.typ == 'REAL':
         loc = self.getLocation()
         val = self.Consume('REAL')
         return self.setLocation(Constant(val, real), loc)
      elif self.token.typ == 'CHAR':
          val = self.Consume('CHAR')
          return Constant(val, char)
      elif self.token.typ == 'STRING':
         txt = self.Consume('STRING')
         return StringConstant(txt)
      elif self.token.typ in ['true', 'false']:
         val = self.Consume()
         val = True if val == 'true' else False
         return Constant(val, boolean)
      elif self.hasConsumed('nil'):
         return Constant(0, NilType())
      elif self.hasConsumed('not'):
         f = self.parseFactor()
         if not isType(f.typ, boolean):
            self.Error('argument of boolean negation must be boolean type')
         return Unop(f, 'not', boolean)
      elif self.token.typ == 'ID':
          designator = self.parseDesignator()
          # TODO: handle functions different here?
          if self.token.typ == '(' and type(designator.typ) is ProcedureType:
             return self.parseProcedureCall(designator)
          else:
             return designator
      else:
         self.Error('Expected NUMBER, ID or ( expr ), got'+str(self.token))

   def parseSimpleExpression(self):
      """ Arithmatic expression """
      if self.token.typ in ['+', '-']:
         # Handle the unary minus
         op = self.Consume()
         a = self.parseTerm()
         typ = a.typ
         if not isType(typ,real) and not isType(typ, integer):
            self.Error('Unary minus or plus can be only applied to real or integers')
         if op == '-':
            a = Unop(a, op, typ)
      else:
         a = self.parseTerm()
      while self.token.typ in ['+', '-', 'or']:
           loc = self.getLocation()
           op = self.Consume()
           b = self.parseTerm()
           if op in ['+', '-']:
              if isType(a.typ, real) or isType(b.typ, real):
                 typ = real
                 if isType(a.typ, integer):
                    # Automatic type cast
                    a = Unop(a, 'INTTOREAL', real)
                 if not isType(a.typ, real):
                    self.Error('first operand must be a real!')
                 if isType(b.typ, integer):
                    b = Unop(b, 'INTTOREAL', real)
                 if not isType(b.typ, real):
                    self.Error('second operand must be a real!')
              elif isType(a.typ, integer) and isType(b.typ, integer):
                 typ = integer
              else:
                 self.Error('Invalid types {0} and {1}'.format(a.typ, b.typ))
           elif op == 'or':
              if not isType(a.typ, boolean):
                 self.Error('first operand must be boolean for or operation')
              if not isType(b.typ, boolean):
                 self.Error('second operand must be boolean for or operation')
              typ = boolean
           else:
              self.Error('Unknown operand {0}'.format(op))
           a = self.setLocation(Binop(a, op, b, typ), loc)
      return a