# ----------------------------------------------------------------------------
#  Grammar for the Calc language
# ----------------------------------------------------------------------------

"""

PROGRAM    ::= '[' 'calc' ',' STATEMENTS ']'

STATEMENTS ::= STATEMENT
               | STATEMENT ',' STATEMENTS

STATEMENT  ::= ASSIGNMENT
               | REPETITION
               | SELECTION
               | INPUT
               | OUTPUT

ASSIGNMENT ::= '[' 'set' ',' VARIABLE ',' EXPRESSION ']'

REPETITION ::= '[' 'while' ',' CONDITION ',' STATEMENTS ']'

SELECTION  ::= '[' 'if' ',' CONDITION ',' STATEMENT ']'
               | '[' 'if' ',' CONDITION ',' STATEMENT ',' STATEMENT ']'

INPUT      ::= '[' 'read' ',' VARIABLE ']'

OUTPUT     ::= '[' 'print' ',' VARIABLE ']'

EXPRESSION ::= CONSTANT
               | VARIABLE
               | BINARYEXPR

BINARYEXPR ::= '[' EXPRESSION ',' BINARYOPER ',' EXPRESSION ']'

CONDITION  ::= '[' EXPRESSION ',' CONDOPER ',' EXPRESSION ']'

BINARYOPER ::= '+' | '-' | '*' | '/'

CONDOPER   ::= '<' | '>' | '='

VARIABEL   ::= a Python string

KONSTANT   ::= a Python number

"""

# ----------------------------------------------------------------------------
#  Primitive functions for the Calc language constructs
# ----------------------------------------------------------------------------

# ----- PROGRAM -----

def isprogram(p):
    return isinstance(p, list) and len(p) > 1 and p[0] == 'calc'

def program_statements(p):
    return p[1:]

# ----- STATEMENTS -----

def isstatements(p):
    isstmnt = lambda s: isassignment(s) or isrepetition(s) or isselection(s) \
                        or isoutput(s) or isinput(s)
    return isinstance(p, list) and p and all(map(isstmnt, p))

def first_statement(p):
    return p[0]

def rest_statements(p):
    return p[1:]

def empty_statements(p):
    return not p

# ----- STATEMENT -----

# No functions for statements in general. Instead, see the differenct
# types of statements: assignments, repetitions, selections, input
# and output.

# ----- ASSIGNMENT -----

def isassignment(p):
    return isinstance(p, list) and len(p) == 3 and p[0] == 'set'

def assignment_variable(p):
    return p[1]

def assignment_expression(p):
    return p[2]

# ----- REPETITION -----

def isrepetition(p):
    return isinstance(p, list) and len(p) > 2 and p[0] == 'while'

def repetition_condition(p):
    return p[1]

def repetition_statements(p):
    return p[2:]

# ----- SELECTION -----

def isselection(p):
    return isinstance(p, list) and (3 <= len(p) <= 4) and p[0] == 'if'

def selection_condition(p):
    return p[1]

def selection_true(p):
    return p[2]

def hasfalse(p):
    return len(p) == 4

def selection_false(p):
    return p[3]

# ----- INPUT -----

def isinput(p):
    return isinstance(p, list) and len(p) == 2 and p[0] == 'read'

def input_variable(p):
    return p[1]

# ----- OUTPUT -----

def isoutput(p):
    return isinstance(p, list) and len(p) == 2 and p[0] == 'print'

def output_variable(p):
    return p[1]

# ----- EXPRESSION -----

# No functions for expressions in general. Instead, see the differenct
# types of expressions: constants, variables and binary expressions.

# ----- BINARYEXPR -----

def isbinary(p):
    return isinstance(p, list) and len(p) == 3 and isbinaryoper(p[1])

def binary_operator(p):
    return p[1]

def binary_left(p):
    return p[0]

def binary_right(p):
    return p[2]

# ----- CONDITION -----

def iscondition(p):
    return isinstance(p, list) and len(p) == 3 and iscondoper(p[1])

def condition_operator(p):
    return p[1]

def condition_left(p):
    return p[0]

def condition_right(p):
    return p[2]

# ----- BINARYOPER -----

def isbinaryoper(p):
    return p in ['+', '-', '*', '/']

# ----- CONDOPER -----

def iscondoper(p):
    return p in ['<', '>', '=']

# ----- VARIABLE -----

def isvariable(p):
    return isinstance(p, str) and p != ""

# ----- CONSTANT -----

def isconstant(p):
    return isinstance(p, int) or isinstance(p, float)