|
| 1 | +# ---------------------------------------------------------------------------- |
| 2 | +# Grammar for the Calc language |
| 3 | +# ---------------------------------------------------------------------------- |
| 4 | + |
| 5 | +""" |
| 6 | +
|
| 7 | +PROGRAM ::= [ 'calc', STATEMENTS ] |
| 8 | +
|
| 9 | +STATEMENTS ::= STATEMENT |
| 10 | + | STATEMENT, STATEMENTS |
| 11 | +
|
| 12 | +STATEMENT ::= ASSIGNMENT |
| 13 | + | REPETITION |
| 14 | + | SELECTION |
| 15 | + | INPUT |
| 16 | + | OUTPUT |
| 17 | +
|
| 18 | +ASSIGNMENT ::= [ 'set', VARIABLE, EXPRESSION ] |
| 19 | +
|
| 20 | +REPETITION ::= [ 'while', CONDITION, STATEMENTS ] |
| 21 | +
|
| 22 | +SELECTION ::= [ 'if', CONDITION, STATEMENT ] |
| 23 | + | [ 'if', CONDITION, STATEMENT, STATEMENT ] |
| 24 | +
|
| 25 | +INPUT ::= [ 'read', VARIABLE ] |
| 26 | +
|
| 27 | +OUTPUT ::= [ 'print', VARIABLE ] |
| 28 | +
|
| 29 | +EXPRESSION ::= CONSTANT |
| 30 | + | VARIABLE |
| 31 | + | BINARYEXPR |
| 32 | +
|
| 33 | +BINARYEXPR ::= [ EXPRESSION, BINARYOPER, EXPRESSION ] |
| 34 | +
|
| 35 | +CONDITION ::= [ EXPRESSION, CONDOPER, EXPRESSION ] |
| 36 | +
|
| 37 | +BINARYOPER ::= '+' | '-' | '*' | '/' |
| 38 | +
|
| 39 | +CONDOPER ::= '<' | '>' | '=' |
| 40 | +
|
| 41 | +VARIABEL ::= a Python string |
| 42 | +
|
| 43 | +KONSTANT ::= a Python number |
| 44 | +
|
| 45 | +""" |
| 46 | + |
| 47 | +# ---------------------------------------------------------------------------- |
| 48 | +# Primitive functions for the Calc language constructs |
| 49 | +# ---------------------------------------------------------------------------- |
| 50 | + |
| 51 | +# ----- PROGRAM ----- |
| 52 | + |
| 53 | +def isprogram(p): |
| 54 | + return isinstance(p, list) and len(p) > 1 and p[0] == 'calc' |
| 55 | + |
| 56 | +def program_statements(p): |
| 57 | + return p[1:] |
| 58 | + |
| 59 | +# ----- STATEMENTS ----- |
| 60 | + |
| 61 | +def isstatements(p): |
| 62 | + isstmnt = lambda s: isassignment(s) or isrepetition(s) or isselection(s) \ |
| 63 | + or isoutput(s) or isinput(s) |
| 64 | + return isinstance(p, list) and p and all(map(isstmnt, p)) |
| 65 | + |
| 66 | +def first_statement(p): |
| 67 | + return p[0] |
| 68 | + |
| 69 | +def rest_statements(p): |
| 70 | + return p[1:] |
| 71 | + |
| 72 | +def empty_statements(p): |
| 73 | + return not p |
| 74 | + |
| 75 | +# ----- STATEMENT ----- |
| 76 | + |
| 77 | +# No functions for statements in general. Instead, see the differenct |
| 78 | +# types of statements: assignments, repetitions, selections, input |
| 79 | +# and output. |
| 80 | + |
| 81 | +# ----- ASSIGNMENT ----- |
| 82 | + |
| 83 | +def isassignment(p): |
| 84 | + return isinstance(p, list) and len(p) == 3 and p[0] == 'set' |
| 85 | + |
| 86 | +def assignment_variable(p): |
| 87 | + return p[1] |
| 88 | + |
| 89 | +def assignment_expression(p): |
| 90 | + return p[2] |
| 91 | + |
| 92 | +# ----- REPETITION ----- |
| 93 | + |
| 94 | +def isrepetition(p): |
| 95 | + return isinstance(p, list) and len(p) > 2 and p[0] == 'while' |
| 96 | + |
| 97 | +def repetition_condition(p): |
| 98 | + return p[1] |
| 99 | + |
| 100 | +def repetition_statements(p): |
| 101 | + return p[2:] |
| 102 | + |
| 103 | +# ----- SELECTION ----- |
| 104 | + |
| 105 | +def isselection(p): |
| 106 | + return isinstance(p, list) and (3 <= len(p) <= 4) and p[0] == 'if' |
| 107 | + |
| 108 | +def selection_condition(p): |
| 109 | + return p[1] |
| 110 | + |
| 111 | +def selection_true(p): |
| 112 | + return p[2] |
| 113 | + |
| 114 | +def hasfalse(p): |
| 115 | + return len(p) == 4 |
| 116 | + |
| 117 | +def selection_false(p): |
| 118 | + return p[3] |
| 119 | + |
| 120 | +# ----- INPUT ----- |
| 121 | + |
| 122 | +def isinput(p): |
| 123 | + return isinstance(p, list) and len(p) == 2 and p[0] == 'read' |
| 124 | + |
| 125 | +def input_variable(p): |
| 126 | + return p[1] |
| 127 | + |
| 128 | +# ----- OUTPUT ----- |
| 129 | + |
| 130 | +def isoutput(p): |
| 131 | + return isinstance(p, list) and len(p) == 2 and p[0] == 'print' |
| 132 | + |
| 133 | +def output_variable(p): |
| 134 | + return p[1] |
| 135 | + |
| 136 | +# ----- EXPRESSION ----- |
| 137 | + |
| 138 | +# No functions for expressions in general. Instead, see the differenct |
| 139 | +# types of expressions: constants, variables and binary expressions. |
| 140 | + |
| 141 | +# ----- BINARYEXPR ----- |
| 142 | + |
| 143 | +def isbinary(p): |
| 144 | + return isinstance(p, list) and len(p) == 3 and isbinaryoper(p[1]) |
| 145 | + |
| 146 | +def binary_operator(p): |
| 147 | + return p[1] |
| 148 | + |
| 149 | +def binary_left(p): |
| 150 | + return p[0] |
| 151 | + |
| 152 | +def binary_right(p): |
| 153 | + return p[2] |
| 154 | + |
| 155 | +# ----- CONDITION ----- |
| 156 | + |
| 157 | +def iscondition(p): |
| 158 | + return isinstance(p, list) and len(p) == 3 and iscondoper(p[1]) |
| 159 | + |
| 160 | +def condition_operator(p): |
| 161 | + return p[1] |
| 162 | + |
| 163 | +def condition_left(p): |
| 164 | + return p[0] |
| 165 | + |
| 166 | +def condition_right(p): |
| 167 | + return p[2] |
| 168 | + |
| 169 | +# ----- BINARYOPER ----- |
| 170 | + |
| 171 | +def isbinaryoper(p): |
| 172 | + return p in ['+', '-', '*', '/'] |
| 173 | + |
| 174 | +# ----- CONDOPER ----- |
| 175 | + |
| 176 | +def iscondoper(p): |
| 177 | + return p in ['<', '>', '='] |
| 178 | + |
| 179 | +# ----- VARIABLE ----- |
| 180 | + |
| 181 | +def isvariable(p): |
| 182 | + return isinstance(p, str) and p != "" |
| 183 | + |
| 184 | +# ----- CONSTANT ----- |
| 185 | + |
| 186 | +def isconstant(p): |
| 187 | + return isinstance(p, int) or isinstance(p, float) |
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