--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/python/libs/compiler/parser.py	Sun Oct 07 17:04:10 2012 +0200
@@ -0,0 +1,787 @@
+"""
+  This module parses source code into an abstract syntax tree (AST)
+"""
+
+from .symboltable import SymbolTable
+from .nodes import *
+from .errors import CompilerException, Error
+from .modules import loadModule
+from .display import printNode
+from .builtin import *
+from . import assembler
+
+class Parser:
+   def __init__(self, tokens):
+      """ provide the parser with the tokens iterator from the lexer. """
+      self.tokens = tokens
+      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):
+       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
+