AdaGenerator.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
    OpenGEODE - A tiny SDL Editor for TASTE

    This module generates Ada code from SDL process models.
    The Ada code is compliant with the TASTE interfaces, and is
    using the ASN.1 "Space-Certified" compiler for data type definition.
    (See TASTE documentation for more information)

    The design is flexible and can be used as basis for other backends.

    Entry point:
    The AST of the model that is parsed is described in ogAST.py

    A Visitor Pattern using Python's "singledispatch" mechanism is used
    to go through the AST and generate code for each SDL construct.

    There is a single function called "generate", decorated with the
    singledispatch mechanism, that needs to be called to generate the code
    of any AST element.

    The generate function returns two values: "code" and "local_decl",
    containing a set of statements and a set of local variables
    (that can be later placed anywhere in the code).

    Expressions (all classes derived from ogAST.Expression) are generated
    using the "expression" visitor (singledispatch set of function).

    Expressions return three values: "code", "ada_string" and "local_decl".
    The "ada_string" value is the usable string that corresponds
    to the result of the expression evaluation.

    For example, take the SDL statement "OUTPUT hello(a+5)"

    This results (in TASTE terminology) in calling the required interface
    called "hello" and passing a parameter of an ASN.1 type (say MyInteger).
    The parameter is always passed by reference.

    It is therefore necessary to build a temporary variable to hold the result
    of the "a+5" expression.

    In this example, the "generate" function will return:
    local_decl = ["tmp01 : MyInteger;"]
    (The template backend can then place it wherever appropriate)

    and code = ["tmp01 := a + 5;", "hello(tmp01);"]
    (The template will then do a '\n'.join(code) - and add indents, etc.)

    To know about "tmp01" and generate the code "hello(tmp01);",
    the function will recursively call "generate" and
    pass a+5 as parameter. The call will return the tuple:

    local_decl = ["tmp01 : MyInteger;"]
    code = ["tmp01 := a + 5;"]
    ada_string = "tmp01"

    This design allows to have any level of complexity in the embedded
    expression in a way that is easy to handle (adding constructs with
    this pattern is straightforward, once the generate function for each AST
    entry is properly implemented).

    Copyright (c) 2012-2013 European Space Agency

    Designed and implemented by Maxime Perrotin

    Contact: maxime.perrotin@esa.int
"""


import logging
from singledispatch import singledispatch

import ogAST
import Helper

LOG = logging.getLogger(__name__)

__all__ = ['generate']

# reference to the ASN.1 Data view and to the visible variables (in scope)
TYPES = None
VARIABLES = {}
LOCAL_VAR = {}
# List of output signals and procedures
OUT_SIGNALS = []
PROCEDURES = []


@singledispatch
def generate(ast):
    ''' Generate the code for an item of the AST '''
    raise TypeError('[AdaGenerator] Unsupported AST construct')
    return [], []


# Processing of the AST
@generate.register(ogAST.Process)
def _process(process):
    ''' Generate the code for a complete process (AST Top level) '''
    process_name = process.processName
    global TYPES
    TYPES = process.dataview
    del OUT_SIGNALS[:]
    del PROCEDURES[:]
    OUT_SIGNALS.extend(process.output_signals)
    PROCEDURES.extend(process.procedures)

    LOG.info('Generating Ada code for process ' + str(process_name))

    # In case model has nested states, flatten everything
    Helper.flatten(process, sep=u'\u00dc')

    # Make an maping {input: {state: transition...}} in order to easily
    # generate the lookup tables for the state machine runtime
    mapping = Helper.map_input_state(process)

    VARIABLES.update(process.variables)

    # Generate the code to declare process-level variables
    process_level_decl = []
    for var_name, (var_type, def_value) in process.variables.viewitems():
        if def_value:
            # Expression must be a ground expression, i.e. must not
            # require temporary variable to store computed result
            dst, dstr, dlocal = expression(def_value)
            varbty = find_basic_type(var_type)
            if varbty.kind in ('SequenceOfType', 'OctetStringType'):
                dstr = array_content(def_value, dstr, varbty)
            assert not dst and not dlocal, 'DCL: Expecting a ground expression'
        process_level_decl.append(
                u'l_{n} : aliased asn1Scc{t}{default};'.format(
                        n=var_name,
                        t=var_type.ReferencedTypeName.replace('-', '_'),
                        default=u' := ' + dstr if def_value else u''))

    # Add the process states list to the process-level variables
    statelist = ', '.join(name for name in process.mapping.iterkeys()
                             if not name.endswith(u'START')) or 'No_State'
    if statelist:
        states_decl = u'type states is ({});'.format(statelist)
        process_level_decl.append(states_decl)
        process_level_decl.append('state : states;')

    for name, val in process.mapping.viewitems():
        if name.endswith(u'START') and name != u'START':
            process_level_decl.append(u'{name} : constant := {val};'
                                      .format(name=name, val=str(val)))

    # Add function allowing to trace current state as a string
    #process_level_decl.append('function get_state return String;')
    #process_level_decl.append('pragma export(C, get_state, "{}_state");'
    #                                                    .format(process_name))

    # Add the declaration of the runTransition procedure
    process_level_decl.append('procedure runTransition(Id: Integer);')

    # Generate the code of the start transition:
    start_transition = ['begin',
                        'runTransition(0);']

    # Generate the TASTE template
    try:
        asn1_modules = '\n'.join(['with {dv};\nuse {dv};'.format(
            dv=dv.replace('-', '_'))
            for dv in process.asn1Modules])
        asn1_modules += '\nwith adaasn1rtl;\nuse adaasn1rtl;'
    except TypeError:
        asn1_modules = '--  No ASN.1 data types are used in this model'
    taste_template = ['''\
-- This file was generated automatically: DO NOT MODIFY IT !

with System.IO;
use System.IO;

with Ada.Unchecked_Conversion;
with Ada.Numerics.Generic_Elementary_Functions;

{dataview}

with Interfaces;
use Interfaces;

package body {process_name} is'''.format(process_name=process_name,
    dataview=asn1_modules)]

    # Generate the source file (.ads) header
    ads_template = ['''\
-- This file was generated automatically: DO NOT MODIFY IT !

{dataview}

package {process_name} is'''.format(process_name=process_name,
                                    dataview=asn1_modules)]

    # Generate the the code of the procedures
    inner_procedures_code = []
    for proc in process.content.inner_procedures:
        proc_code, proc_local = generate(proc)
        process_level_decl.extend(proc_local)
        inner_procedures_code.extend(proc_code)

    # Generate the code for the process-level variable declarations
    taste_template.extend(process_level_decl)

    # Add the code of the procedures definitions
    taste_template.extend(inner_procedures_code)

    # Generate the code for each input signal (provided interface) and timers
    for signal in process.input_signals + [
                        {'name': timer.lower()} for timer in process.timers]:
        if signal.get('name', u'START') == u'START':
            continue
        pi_header = 'procedure {sig_name}'.format(sig_name=signal['name'])
        param_name = signal.get('param_name') or 'MISSING_PARAM_NAME'
        # Add (optional) PI parameter (only one is possible in TASTE PI)
        if 'type' in signal:
            typename = signal['type'].ReferencedTypeName.replace('-', '_')
            pi_header += '({pName}: access asn1Scc{pType})'.format(
                                        pName=param_name, pType=typename)

        # Add declaration of the provided interface in the .ads file
        ads_template.append('--  Provided interface "' + signal['name'] + '"')
        ads_template.append(pi_header + ';')
        ads_template.append('pragma export(C, {name}, "{proc}_{name}");'
                            .format(name=signal['name'], proc=process_name))

        pi_header += ' is'
        taste_template.append(pi_header)
        taste_template.append('begin')
        taste_template.append('case state is')
        for state in process.mapping.viewkeys():
            if state.endswith(u'START'):
                continue
            taste_template.append(u'when {state} =>'.format(state=state))
            input_def = mapping[signal['name']].get(state)
            # Check for nested states to call optional exit procedure
            sep = u'\u00dc'
            state_tree = state.split(sep)
            context = process
            exitlist = []
            current = ''
            trans = input_def and process.transitions[input_def.transition_id]
            while state_tree:
                current = current + state_tree.pop(0)
                for comp in context.composite_states:
                    if current.lower() == comp.statename.lower():
                        if comp.exit_procedure:
                            exitlist.append(current)
                        context = comp
                        current = current + sep
                        break
            for each in reversed(exitlist):
                if trans and all(each.startswith(trans_st)
                                 for trans_st in trans.possible_states):
                    taste_template.append(each + sep + u'exit;')

            if input_def:
                for inp in input_def.parameters:
                    # Assign the (optional and unique) parameter
                    # to the corresponding process variable
                    taste_template.append(u'l_{inp} := {tInp}.all;'.format(
                        inp=inp, tInp=param_name))
                # Execute the correponding transition
                if input_def.transition:
                    taste_template.append(u'runTransition({idx});'.format(
                        idx=input_def.transition_id))
                else:
                    taste_template.append('null;')
            else:
                taste_template.append('null;')
        taste_template.append('when others =>')
        taste_template.append('null;')
        taste_template.append('end case;')
        taste_template.append(u'end {sig_name};'.format(
                                                    sig_name=signal['name']))
        taste_template.append('\n')

    # for the .ads file, generate the declaration of the required interfaces
    # output signals are the asynchronous RI - only one parameter
    for signal in process.output_signals:
        ri_header = u'procedure {sig_name}'.format(sig_name=signal['name'])
        param_name = signal.get('param_name') or 'MISSING_PARAM_NAME'
        # Add (optional) RI parameter
        if 'type' in signal:
            typename = signal['type'].ReferencedTypeName.replace('-', '_')
            ri_header += u'({pName}: access asn1Scc{pType})'.format(
                pName=param_name, pType=typename)
        ads_template.append(u'--  Required interface "' + signal['name'] + '"')
        ads_template.append(ri_header + ';')
        ads_template.append(u'pragma import(C, {sig}, "{proc}_RI_{sig}");'
                .format(sig=signal['name'], proc=process_name))

    # for the .ads file, generate the declaration of the external procedures
    for proc in (proc for proc in process.procedures if proc.external):
        ri_header = u'procedure {sig_name}'.format(sig_name=proc.inputString)
        params = []
        for param in proc.fpar:
            typename = param['type'].ReferencedTypeName.replace('-', '_')
            params.append(u'{par[name]}: access asn1Scc{partype}'.format(
                par=param, partype=typename))
        if params:
            ri_header += u'(' + u';'.join(params) + ')'
        ads_template.append(
                        u'--  Sync required interface "' + proc.inputString)
        ads_template.append(ri_header + u';')
        ads_template.append(u'pragma import(C, {sig}, "{proc}_RI_{sig}");'
                .format(sig=proc.inputString, proc=process_name))

    # for the .ads file, generate the declaration of timers set/reset functions
    for timer in process.timers:
        ads_template.append(
                u'--  Timer {} SET and RESET functions'.format(timer))
        ads_template.append(u'procedure SET_{}(val: access asn1SccT_UInt32);'
                .format(timer))
        ads_template.append(
                u'pragma import(C, SET_{timer}, "{proc}_RI_set_{timer}");'
                .format(timer=timer, proc=process_name))
        ads_template.append(u'procedure RESET_{};'.format(timer))
        ads_template.append(
                u'pragma import(C, RESET_{timer}, "{proc}_RI_reset_{timer}");'
                .format(timer=timer, proc=process_name))

    taste_template.append('procedure runTransition(Id: Integer) is')
    taste_template.append('trId : Integer := Id;')

    # If the process has no input, output, procedures, or timers, then Ada
    # will not compile the body - generate a pragma to fix this
    if not process.timers and not process.procedures \
            and not process.input_signals and not process.output_signals:
        ads_template.append('pragma elaborate_body;')

    # Transform inner labels to floating labels
    Helper.inner_labels_to_floating(process)

    # Generate the code for all transitions
    code_transitions = []
    local_decl_transitions = []
    for proc_tr in process.transitions:
        code_tr, tr_local_decl = generate(proc_tr)
        code_transitions.append(code_tr)
        local_decl_transitions.extend(tr_local_decl)

    # Generate code for the floating labels
    code_labels = []
    for label in process.content.floating_labels:
        code_label, label_decl = generate(label)
        local_decl_transitions.extend(label_decl)
        code_labels.extend(code_label)

    # Declare the local variables needed by the transitions in the template
    decl = [u'{line}'.format(line=l)
            for l in set(local_decl_transitions)]
    taste_template.extend(decl)
    taste_template.append('begin')

    # Generate a loop that ends when a next state is reached
    # (there can be chained transition when entering a nested state)
    taste_template.append('while (trId /= -1) loop')

    # Generate the switch-case on the transition id
    taste_template.append('case trId is')

    for idx, val in enumerate(code_transitions):
        taste_template.append(u'when {idx} =>'.format(idx=idx))
        val = [u'{line}'.format(line=l) for l in val]
        if val:
            taste_template.extend(val)
        else:
            taste_template.append('null;')

    taste_template.append('when others =>')
    taste_template.append('null;')

    taste_template.append('end case;')
    if code_labels:
        # Due to nested states (chained transitions) jump over label code
        # (NEXTSTATEs do not return from runTransition)
        taste_template.append('goto next_transition;')

    # Add the code for the floating labels
    taste_template.extend(code_labels)

    #if code_labels:
    taste_template.append('<<next_transition>>')
    taste_template.append('null;')
    taste_template.append('end loop;')
    taste_template.append('end runTransition;')
    taste_template.append('\n')

    # Code of the function allowing to trace current state
    #taste_template.append('function get_state return String is')
    #taste_template.append('begin')
    #taste_template.append("return states'Image(state);")
    #taste_template.append('end get_state;')
    #taste_template.append('\n')

    taste_template.extend(start_transition)
    taste_template.append('end {process_name};'
            .format(process_name=process_name))

    ads_template.append('end {process_name};'
            .format(process_name=process_name))

    with open(process_name + '.adb', 'w') as ada_file:
        ada_file.write(
                u'\n'.join(format_ada_code(taste_template)).encode('latin1'))

    with open(process_name + '.ads', 'w') as ada_file:
        ada_file.write(
                u'\n'.join(format_ada_code(ads_template)).encode('latin1'))


def write_statement(param, newline):
    ''' Generate the code for the special "write" operator '''
    code = []
    string = ''
    local = []
    basic_type = find_basic_type(param.exprType) or {}
    type_kind = basic_type.kind
    if isinstance(param, ogAST.ExprAppend):
        # Append: call Put_Line separately for each side of the expression
        st1, _, lcl1= write_statement(param.left, newline = False)
        st2, _, lcl2 = write_statement(param.right, newline = False)
        code.extend(st1)
        code.extend(st2)
        local.extend(lcl1)
        local.extend(lcl2)
    elif type_kind.endswith('StringType'):
        if isinstance(param, ogAST.PrimStringLiteral):
            # Raw string
            code.append(u'Put("{}");'
                        .format(param.value[1:-1].replace('"', "'")))
        else:
            code, string, local = expression(param)
            if type_kind == 'OctetStringType':
                # Octet string -> convert to Ada string
                sep = u'\u00dc'
                last_it = u""
                if isinstance(param, ogAST.PrimSubstring):
                    range_str = u"{}'Range".format(string)
                    iterator = u"i - {}'First + 1".format(string)
                elif basic_type.Min == basic_type.Max:
                    range_str = u"{}.Data'Range".format(string)
                    string += u".Data"
                    iterator = u"i"
                else:
                    range_str = u"1 .. {}.Length".format(string)
                    string += u".Data"
                    iterator = u"i"
                    last_it = u"({})".format(range_str)
                code.extend([u"for i in {} loop".format(range_str),
                             u"Put(Character'Val({st}(i)));"
                             .format(st=string, sep=sep, it=iterator),
                             u"end loop;"])
            else:
                code.append("Put({});".format(string))
    elif type_kind in ('IntegerType', 'RealType',
                       'BooleanType', 'Integer32Type'):
        code, string, local = expression(param)
        if type_kind in ('IntegerType', 'Integer32Type'):
            cast = "Asn1Int"
        elif type_kind == 'RealType':
            cast = 'Long_Float'
        elif type_kind == 'BooleanType':
            cast = 'Boolean'
        code.append(u"Put({cast}'Image({s}));".format(cast=cast, s=string))
    else:
        error = (u'Unsupported parameter in write call ' +
                param.inputString)
        LOG.error(error)
        raise TypeError(error)
    if newline:
        code.append(u"New_Line;")
    return code, string, local


@generate.register(ogAST.Output)
@generate.register(ogAST.ProcedureCall)
def _call_external_function(output):
    ''' Generate the code of a set of output or procedure call statement '''
    code = []
    local_decl = []

    # Add the traceability information
    code.extend(traceability(output))

    for out in output.output:
        signal_name = out['outputName']

        if signal_name.lower() in ('write', 'writeln'):
            # special built-in SDL procedure for printing strings
            # supports printing of native types (int, real, bool)
            # but not yet complex ASN.1 structures (sequence/seqof/choice)
            for param in out['params'][:-1]:
                stmts, _, local = write_statement(param, newline=False)
                code.extend(stmts)
                local_decl.extend(local)
            for param in out['params'][-1:]:
                # Last parameter - add newline if necessary
                stmts, _, local = write_statement(param, newline=True if
                        signal_name.lower() == 'writeln' else False)
                code.extend(stmts)
                local_decl.extend(local)
            continue
        elif signal_name.lower() == 'reset_timer':
            # built-in operator for resetting timers. param = timer name
            param, = out['params']
            p_code, p_id, p_local = expression(param)
            code.extend(p_code)
            local_decl.extend(p_local)
            code.append('RESET_{};'.format(p_id))
            continue
        elif signal_name.lower() == 'set_timer':
            # built-in operator for setting a timer: SET(1000, timer_name)
            timer_value, timer_id = out['params']
            t_code, t_val, t_local = expression(timer_value)
            p_code, p_id, p_local = expression(timer_id)
            code.extend(t_code)
            code.extend(p_code)
            local_decl.extend(t_local)
            local_decl.extend(p_local)
            # Use a temporary variable to store the timer value
            tmp_id = 'tmp' + str(out['tmpVars'][0])
            local_decl.append('{} : aliased asn1SccT_UInt32;'
                              .format(tmp_id))
            code.append('{tmp} := {val};'.format(tmp=tmp_id, val=t_val))
            code.append("SET_{timer}({value}'access);"
                                             .format(timer=p_id, value=tmp_id))
            continue
        proc, out_sig = None, None
        try:
            out_sig, = [sig for sig in OUT_SIGNALS
                        if sig['name'].lower() == signal_name.lower()]
        except ValueError:
            # Not an output, try if it is an external or inner procedure
            try:
                proc, = [sig for sig in PROCEDURES
                            if sig.inputString.lower() == signal_name.lower()]
                if proc.external:
                    out_sig = proc
            except ValueError:
                # Not there? Impossible, the parser would have barked
                raise ValueError('Probably a bug - please report')
        if out_sig:
            list_of_params = []
            for idx, param in enumerate(out.get('params') or []):
                param_direction = 'in'
                try:
                    # If it is an output, there is a single parameter
                    param_type = out_sig['type']
                except TypeError:
                    # Else if it is a procedure, get the type
                    param_type = out_sig.fpar[idx]['type']
                    param_direction = out_sig.fpar[idx]['direction']

                typename = param_type.ReferencedTypeName.replace('-', '_')
                p_code, p_id, p_local = expression(param)
                code.extend(p_code)
                local_decl.extend(p_local)
                # Create a temporary variable for input parameters only
                # (If needed, i.e. if argument is not a local variable)
                if param_direction == 'in' \
                        and (not (isinstance(param, ogAST.PrimVariable)
                        and p_id.startswith('l_'))
                        or isinstance(param, ogAST.PrimFPAR)):
                    tmp_id = out['tmpVars'][idx]
                    local_decl.append('tmp{idx} : aliased asn1Scc{oType};'
                                      .format(idx=tmp_id, oType=typename))
                    if isinstance(param,
                              (ogAST.PrimSequenceOf, ogAST.PrimStringLiteral)):
                        p_id = array_content(param, p_id,
                                             find_basic_type(param_type))
                    code.append('tmp{idx} := {p_id};'
                                .format(idx=tmp_id, p_id=p_id))
                    list_of_params.append("tmp{idx}'access"
                                          .format(idx=out['tmpVars'][idx]))
                else:
                    # Output parameters - no need for a temp variable
                    list_of_params.append(u"{var}'access".format(var=p_id))
            if list_of_params:
                code.append(u'{RI}({params});'.format(
                    RI=out['outputName'], params=', '.join(list_of_params)))
            else:
                code.append(u'{RI};'.format(RI=out['outputName']))
        else:
            # inner procedure call
            list_of_params = []
            for param in out.get('params', []):
                p_code, p_id, p_local = expression(param)
                code.extend(p_code)
                local_decl.extend(p_local)
                # no need to use temporary variables, we are in pure Ada
                list_of_params.append(p_id)
            if list_of_params:
                code.append(u'{proc}({params});'.format(
                    proc=proc.inputString,
                    params=', '.join(list_of_params)))
            else:
                code.append(u'{};'.format(proc.inputString))
    return code, local_decl


@generate.register(ogAST.TaskAssign)
def _task_assign(task):
    ''' A list of assignments in a task symbol '''
    code, local_decl = [], []
    if task.comment:
        code.extend(traceability(task.comment))
    for expr in task.elems:
        code.extend(traceability(expr))
        # ExprAssign only returns code statements, no string
        code_assign, _, decl_assign = expression(expr)
        code.extend(code_assign)
        local_decl.extend(decl_assign)
    return code, local_decl


@generate.register(ogAST.TaskInformalText)
def _task_informal_text(task):
    ''' Generate Ada comments for informal text '''
    code = []
    if task.comment:
        code.extend(traceability(task.comment))
    code.extend(['-- ' + text.replace('\n', '\n-- ') for text in task.elems])
    return code, []


@generate.register(ogAST.TaskForLoop)
def _task_forloop(task):
    '''
        Return the code corresponding to a for loop. Two forms are possible:
        for x in range ([start], stop [, step])
        for x in iterable (a SEQUENCE OF)
    '''
    stmt, local_decl = [], []
    if task.comment:
        stmt.extend(traceability(task.comment))
    stmt.extend(traceability(task))
    for loop in task.elems:
        if loop['range']:
            start_str, stop_str = '0', ''
            if loop['range']['start']:
                start_stmt, start_str, start_local = expression(
                                                    loop['range']['start'])
                local_decl.extend(start_local)
                stmt.extend(start_stmt)
            if loop['range']['step'] == 1:
                start_str += '..'
            stop_stmt, stop_str, stop_local = expression(loop['range']['stop'])
            local_decl.extend(stop_local)
            stmt.extend(stop_stmt)
            if loop['range']['step'] == 1:
                if unicode.isnumeric(stop_str):
                    stop_str = unicode(int(stop_str) - 1)
                else:
                    stop_str = u'{} - 1'.format(stop_str)
                stmt.append(
                        u'for {it} in {start}{stop} loop'
                        .format(it=loop['var'], start=start_str, stop=stop_str))
            else:
                # Step is not directly supported in Ada, we need to use 'while'
                stmt.extend(['declare',
                             u'{it} : Integer := {start};'
                             .format(it=loop['var'],
                             start=start_str),
                             '',
                             'begin',
                             u'while {it} < {stop} loop'.format(it=loop['var'],
                                                               stop=stop_str)])
        else:
            # case of form: FOR x in SEQUENCE OF
            list_stmt, list_str, list_local = expression(loop['list'])
            basic_type = find_basic_type(loop['list'].exprType)
            list_payload = list_str + string_payload(loop['list'], list_str)
            if isinstance(loop['list'], ogAST.PrimSubstring) or \
                    basic_type.Min == basic_type.Max:
                range_str = u"{}'Range".format(list_payload)
            else:
                range_str = u"1 .. {}.Length".format(list_str)
            stmt.extend(list_stmt)
            local_decl.extend(list_local)
            stmt.extend(['declare',
                         '{} : {};'.format(loop['var'],
                                           type_name(loop['type'])),
                         '',
                         'begin',
                         'for {it}_idx in {rc} loop'.format(it=loop['var'],
                                                            rc=range_str),
                         '{it} := {var}({it}_idx);'.format(it=loop['var'],
                                                          var=list_payload)])
        try:
            code_trans, local_trans = generate(loop['transition'])
            if local_trans:
                stmt.append('declare')
                stmt.extend(local_trans)
                stmt.append('')
                stmt.append('begin')
            stmt.extend(code_trans)
            if local_trans:
                stmt.append('end;')
        except AttributeError:
            stmt.append('null;')
        if loop['range'] and loop['range']['step'] != 1:
            stmt.append('{it} := {it} + {step};'.format(it=loop['var'],
                                                   step=loop['range']['step']))
        stmt.append('end loop;')
        if (loop['range'] and loop['range']['step'] != 1) or loop['list']:
            stmt.append('end;')
    return stmt, local_decl


@singledispatch
def expression(expr):
    ''' Generate the code for Expression-classes, returning 3 things:
        - list of statements
        - useable string corresponding to the evaluation of the expression,
        - list of local declarations
    '''
    raise TypeError('Unsupported expression: ' + str(expr))
    return [], '', []


@expression.register(ogAST.PrimVariable)
def _primary_variable(prim):
    ''' Single variable reference '''
    sep = u'l_' if find_var(prim.value[0]) else u''

    ada_string = u'{sep}{name}'.format(sep=sep, name=prim.value[0])

    if prim.exprType.__name__ == 'for_range':
        # Ada iterator in FOR loops is an Integer - we must cast to 64 bits
        ada_string = u'Asn1Int({})'.format(ada_string)
    return [], unicode(ada_string), []


@expression.register(ogAST.PrimCall)
def _prim_call(prim):
    stmts, ada_string, local_decl = [], '', []

    ident = prim.value[0].lower()
    params = prim.value[1]['procParams']

    if ident in ('abs', 'fix', 'float'):
        # Return absolute value of a number
        param_stmts, param_str, local_var = expression(params[0])
        stmts.extend(param_stmts)
        local_decl.extend(local_var)
        ada_string += '{op}({param})'.format(
                param=param_str,
                op='abs' if ident == 'abs' else
                'Asn1Int' if ident == 'fix' else 'Asn1Real'
                if ident == 'float' else 'ERROR')
    elif ident == 'power':
        operands = [None, None]
        for idx, param in enumerate(params):
            stmt, operands[idx], local = expression(param)
            stmts.extend(stmt)
            local_decl.extend(local)
        ada_string += '{op[0]} ** Natural({op[1]})'.format(op=operands)
    elif ident == 'length':
        # Length of sequence of: take only the first parameter
        exp = params[0]
        exp_type = find_basic_type(exp.exprType)
        min_length = getattr(exp_type, 'Min', None)
        max_length = getattr(exp_type, 'Max', None)
        if min_length is None or max_length is None:
            error = '{} is not a SEQUENCE OF'.format(
                    exp.inputString)
            LOG.error(error)
            raise TypeError(error)
        param_stmts, param_str, local_var = expression(exp)
        stmts.extend(param_stmts)
        local_decl.extend(local_var)
        if min_length == max_length \
                and not isinstance(exp, ogAST.PrimSubstring):
            ada_string += min_length
        else:
            if isinstance(exp, ogAST.PrimSubstring):
                range_str = u"{}'Length".format(param_str)
            else:
                range_str = u"{}.Length".format(param_str)
            ada_string += ('Asn1Int({})'.format(range_str))
    elif ident == 'present':
        # User wants to know what CHOICE element is present
        exp = params[0]
        # Get the basic type to make sure it is a choice
        exp_type = find_basic_type(exp.exprType)
        # Also get the ASN.1 type name as it is
        # needed to build the Ada expression
        exp_typename = \
                (getattr(exp.exprType, 'ReferencedTypeName',
                     None) or exp.exprType.kind).replace('-', '_')
        if exp_type.kind != 'ChoiceType':
            error = '{} is not a CHOICE'.format(exp.inputString)
            LOG.error(error)
            raise TypeError(error)
        param_stmts, param_str, local_var = expression(exp)
        stmts.extend(param_stmts)
        local_decl.extend(local_var)
        ada_string += ('asn1Scc{t}_Kind({e})'.format(
            t=exp_typename, e=param_str))
    elif ident == 'num':
        # User wants to get an enumerated corresponding integer value
        exp = params[0]
        # Get the ASN.1 type name as it is needed to build the Ada expression
        exp_typename = \
                (getattr(exp.exprType, 'ReferencedTypeName', None)
                        or exp.exprType.kind).replace('-', '_')
        param_stmts, param_str, local_var = expression(exp)
        local_decl.append('function num_{t} is new Ada.Unchecked_Conversion'
                          '(asn1scc{t}, Asn1Int);'.format(t=exp_typename))
        stmts.extend(param_stmts)
        local_decl.extend(local_var)
        ada_string += ('num_{t}({p})'.format(t=exp_typename, p=param_str))
    elif ident == 'floor':
        # Get the ASN.1 type name as it is needed to build the Ada expression
        exp = params[0]
        exp_typename = (getattr(exp.exprType, 'ReferencedTypeName', None)
                        or 'Long_Float').replace('-', '_')
        param_stmts, param_str, local_var = expression(exp)
        stmts.extend(param_stmts)
        local_decl.extend(local_var)
        ada_string += "{t}'Floor({p})".format(t=exp_typename, p=param_str)
    elif ident == 'ceil':
        # Get the ASN.1 type name as it is needed to build the Ada expression
        exp = params[0]
        exp_typename = (getattr(exp.exprType, 'ReferencedTypeName', None)
                        or 'Long_Float').replace('-', '_')
        param_stmts, param_str, local_var = expression(exp)
        stmts.extend(param_stmts)
        local_decl.extend(local_var)
        ada_string += "{t}'Ceiling({p})".format(t=exp_typename, p=param_str)
    elif ident == 'cos':
        exp = params[0]
        param_stmts, param_str, local_var = expression(exp)
        stmts.extend(param_stmts)
        local_decl.extend(local_var)
        local_decl.append('package Math is new '
                          'Ada.Numerics.Generic_Elementary_Functions'
                          '(Long_Float);')
        ada_string += "Math.Cos({})".format(param_str)
    elif ident == 'round':
        exp = params[0]
        # Get the ASN.1 type name as it is needed to build the Ada expression
        exp_typename = (getattr(exp.exprType, 'ReferencedTypeName', None)
                        or 'Long_Float').replace('-', '_')
        param_stmts, param_str, local_var = expression(exp)
        stmts.extend(param_stmts)
        local_decl.extend(local_var)
        ada_string += "{t}'Rounding({p})".format(t=exp_typename, p=param_str)
    elif ident == 'sin':
        exp = params[0]
        param_stmts, param_str, local_var = expression(exp)
        stmts.extend(param_stmts)
        local_decl.extend(local_var)
        local_decl.append('package Math is new '
                          'Ada.Numerics.Generic_Elementary_Functions'
                          '(Long_Float);')
        ada_string += "Math.Sin({})".format(param_str)
    elif ident == 'sqrt':
        exp = params[0]
        param_stmts, param_str, local_var = expression(exp)
        stmts.extend(param_stmts)
        local_decl.extend(local_var)
        local_decl.append('package Math is new '
                          'Ada.Numerics.Generic_Elementary_Functions'
                          '(Long_Float);')
        ada_string += "Math.Sqrt({})".format(param_str)
    elif ident == 'trunc':
        exp = params[0]
        # Get the ASN.1 type name as it is needed to build the Ada expression
        exp_typename = (getattr(exp.exprType, 'ReferencedTypeName', None)
                        or 'Long_Float').replace('-', '_')
        param_stmts, param_str, local_var = expression(exp)
        stmts.extend(param_stmts)
        local_decl.extend(local_var)
        ada_string += "{t}'Truncation({p})".format(t=exp_typename, p=param_str)
    else:
        ada_string += '('
        # Take all params and join them with commas
        list_of_params = []
        for param in params:
            param_stmt, param_str, local_var = (expression(param))
            list_of_params.append(param_str)
            stmts.extend(param_stmt)
            local_decl.extend(local_var)
        ada_string += ', '.join(list_of_params)
        ada_string += ')'

    return stmts, unicode(ada_string), local_decl


@expression.register(ogAST.PrimIndex)
def _prim_index(prim):
    stmts, ada_string, local_decl = [], '', []

    receiver = prim.value[0]

    receiver_stms, reciver_string, receiver_decl = expression(receiver)
    ada_string = reciver_string
    stmts.extend(receiver_stms)
    local_decl.extend(receiver_decl)

    idx_stmts, idx_string, idx_var = expression(prim.value[1]['index'][0])
    if unicode.isnumeric(idx_string):
        idx_string = int(idx_string) + 1
    else:
        idx_string = '1+Integer({idx})'.format(idx=idx_string)
    if not isinstance(receiver, ogAST.PrimSubstring):
        ada_string += '.Data'
    ada_string += '({idx})'.format(idx=idx_string)
    stmts.extend(idx_stmts)
    local_decl.extend(idx_var)

    return stmts, unicode(ada_string), local_decl


@expression.register(ogAST.PrimSubstring)
def _prim_substring(prim):
    ''' Generate expression for SEQOF/OCT.STRING substrings, e.g. foo(1,2) '''
    stmts, ada_string, local_decl = [], '', []

    receiver = prim.value[0]

    receiver_stms, reciver_string, receiver_decl = expression(receiver)
    ada_string = reciver_string
    stmts.extend(receiver_stms)
    local_decl.extend(receiver_decl)

    r1_stmts, r1_string, r1_local = expression(prim.value[1]['substring'][0])
    r2_stmts, r2_string, r2_local = expression(prim.value[1]['substring'][1])

    # Adding 1 because SDL starts indexes at 0, ASN1 Ada types at 1
    if unicode.isnumeric(r1_string):
        r1_string = unicode(int(r1_string) + 1)
    else:
        r1_string += ' + 1'
    if unicode.isnumeric(r2_string):
        r2_string = unicode(int(r2_string) + 1)
    else:
        r2_string += ' + 1'

    if not isinstance(receiver, ogAST.PrimSubstring):
        ada_string += '.Data'
    ada_string += '({r1}..{r2})'.format(r1=r1_string, r2=r2_string)
    stmts.extend(r1_stmts)
    stmts.extend(r2_stmts)
    local_decl.extend(r1_local)
    local_decl.extend(r2_local)

    return stmts, unicode(ada_string), local_decl


@expression.register(ogAST.PrimSelector)
def _prim_selector(prim):
    stmts, ada_string, local_decl = [], '', []

    receiver = prim.value[0]
    field_name = prim.value[1]

    receiver_stms, reciver_string, receiver_decl = expression(receiver)
    ada_string = reciver_string
    stmts.extend(receiver_stms)
    local_decl.extend(receiver_decl)

    receiver_bty = find_basic_type(receiver.exprType)
    receiver_ty_name = receiver.exprType.ReferencedTypeName.replace('-', '_')

    if receiver_bty.kind == 'ChoiceType':
        ada_string = ('asn1Scc{typename}_{field_name}_get({ada_string})'
                    .format(typename=receiver_ty_name,
                            field_name=field_name,
                            ada_string=ada_string))
    else:
        ada_string += '.' + field_name

    return stmts, unicode(ada_string), local_decl


@expression.register(ogAST.ExprPlus)
@expression.register(ogAST.ExprMul)
@expression.register(ogAST.ExprMinus)
@expression.register(ogAST.ExprGt)
@expression.register(ogAST.ExprGe)
@expression.register(ogAST.ExprLt)
@expression.register(ogAST.ExprLe)
@expression.register(ogAST.ExprDiv)
@expression.register(ogAST.ExprMod)
@expression.register(ogAST.ExprRem)
def _basic_operators(expr):
    ''' Expressions with two sides '''
    code, local_decl = [], []
    left_stmts, left_str, left_local = expression(expr.left)
    right_stmts, right_str, right_local = expression(expr.right)
    ada_string = u'({left} {op} {right})'.format(
            left=left_str, op=expr.operand, right=right_str)
    code.extend(left_stmts)
    code.extend(right_stmts)