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|
# ----------------------------------------------------------------------------
# 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)
|
