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#
# decaf_parser.py
#
# Rudimentary parser for decaf language, used in Stanford University CS143
# (https://web.stanford.edu/class/archive/cs/cs143/cs143.1128/handouts/030%20Decaf%20Specification.pdf)
#
# To convert this parser into one that gives more of an AST, change all the Group wrappers to add parse
# actions that will result in ASTNode classes, or statement-specific subclasses.
#
# Copyright 2018, Paul McGuire
#
"""
Program ::= Decl+
Decl ::= VariableDecl | FunctionDecl | ClassDecl | InterfaceDecl
VariableDecl ::= Variable ;
Variable ::= Type ident
Type ::= int | double | bool | string | ident | Type []
FunctionDecl ::= Type ident ( Formals ) StmtBlock | void ident ( Formals ) StmtBlock
Formals ::= Variable+, | e
ClassDecl ::= class ident <extends ident> <implements ident + ,> { Field* }
Field ::= VariableDecl | FunctionDecl
InterfaceDecl ::= interface ident { Prototype* }
Prototype ::= Type ident ( Formals ) ; | void ident ( Formals ) ;
StmtBlock ::= { VariableDecl* Stmt* }
Stmt ::= <Expr> ; | IfStmt | WhileStmt | ForStmt | BreakStmt | ReturnStmt | PrintStmt | StmtBlock
IfStmt ::= if ( Expr ) Stmt <else Stmt>
WhileStmt ::= while ( Expr ) Stmt
ForStmt ::= for ( <Expr> ; Expr ; <Expr> ) Stmt
ReturnStmt ::= return <Expr> ;
BreakStmt ::= break ;
PrintStmt ::= Print ( Expr+, ) ;
Expr ::= LValue = Expr | Constant | LValue | this | Call
| ( Expr )
| Expr + Expr | Expr - Expr | Expr * Expr | Expr / Expr | Expr % Expr | - Expr
| Expr < Expr | Expr <= Expr | Expr > Expr | Expr >= Expr | Expr == Expr | Expr != Expr
| Expr && Expr | Expr || Expr | ! Expr
| ReadInteger ( ) | ReadLine ( ) | new ident | NewArray ( Expr , Typev)
LValue ::= ident | Expr . ident | Expr [ Expr ]
Call ::= ident ( Actuals ) | Expr . ident ( Actuals )
Actuals ::= Expr+, | e
Constant ::= intConstant | doubleConstant | boolConstant | stringConstant | null
"""
import pyparsing as pp
from pyparsing import pyparsing_common as ppc
pp.ParserElement.enablePackrat()
# keywords
keywords = (
VOID,
INT,
DOUBLE,
BOOL,
STRING,
CLASS,
INTERFACE,
NULL,
THIS,
EXTENDS,
IMPLEMENTS,
FOR,
WHILE,
IF,
ELSE,
RETURN,
BREAK,
NEW,
NEWARRAY,
PRINT,
READINTEGER,
READLINE,
TRUE,
FALSE,
) = map(
pp.Keyword,
"""void int double bool string class interface null this extends implements or while
if else return break new NewArray Print ReadInteger ReadLine true false""".split(),
)
keywords = pp.MatchFirst(list(keywords))
LPAR, RPAR, LBRACE, RBRACE, LBRACK, RBRACK, DOT, EQ, COMMA, SEMI = map(
pp.Suppress, "(){}[].=,;"
)
hexConstant = pp.Regex(r"0[xX][0-9a-fA-F]+").addParseAction(lambda t: int(t[0][2:], 16))
intConstant = hexConstant | ppc.integer
doubleConstant = ppc.real
boolConstant = TRUE | FALSE
stringConstant = pp.dblQuotedString
null = NULL
constant = doubleConstant | boolConstant | intConstant | stringConstant | null
ident = ~keywords + pp.Word(pp.alphas, pp.alphanums + "_")
type_ = pp.Group((INT | DOUBLE | BOOL | STRING | ident) + pp.ZeroOrMore("[]"))
variable = type_ + ident
variable_decl = variable + SEMI
expr = pp.Forward()
expr_parens = pp.Group(LPAR + expr + RPAR)
actuals = pp.Optional(pp.delimitedList(expr))
call = pp.Group(
ident("call_ident") + LPAR + actuals("call_args") + RPAR
| (expr_parens + pp.ZeroOrMore(DOT + ident))("call_ident_expr")
+ LPAR
+ actuals("call_args")
+ RPAR
)
lvalue = (
(ident | expr_parens)
+ pp.ZeroOrMore(DOT + (ident | expr_parens))
+ pp.ZeroOrMore(LBRACK + expr + RBRACK)
)
assignment = pp.Group(lvalue("lhs") + EQ + expr("rhs"))
read_integer = pp.Group(READINTEGER + LPAR + RPAR)
read_line = pp.Group(READLINE + LPAR + RPAR)
new_statement = pp.Group(NEW + ident)
new_array = pp.Group(NEWARRAY + LPAR + expr + COMMA + type_ + RPAR)
rvalue = constant | call | read_integer | read_line | new_statement | new_array | ident
arith_expr = pp.infixNotation(
rvalue,
[
(
"-",
1,
pp.opAssoc.RIGHT,
),
(
pp.oneOf("* / %"),
2,
pp.opAssoc.LEFT,
),
(
pp.oneOf("+ -"),
2,
pp.opAssoc.LEFT,
),
],
)
comparison_expr = pp.infixNotation(
arith_expr,
[
(
"!",
1,
pp.opAssoc.RIGHT,
),
(
pp.oneOf("< > <= >="),
2,
pp.opAssoc.LEFT,
),
(
pp.oneOf("== !="),
2,
pp.opAssoc.LEFT,
),
(
pp.oneOf("&&"),
2,
pp.opAssoc.LEFT,
),
(
pp.oneOf("||"),
2,
pp.opAssoc.LEFT,
),
],
)
expr <<= (
assignment
| call
| THIS
| comparison_expr
| arith_expr
| lvalue
| constant
| read_integer
| read_line
| new_statement
| new_array
)
stmt = pp.Forward()
print_stmt = pp.Group(
PRINT("statement")
+ LPAR
+ pp.Group(pp.Optional(pp.delimitedList(expr)))("args")
+ RPAR
+ SEMI
)
break_stmt = pp.Group(BREAK("statement") + SEMI)
return_stmt = pp.Group(RETURN("statement") + expr + SEMI)
for_stmt = pp.Group(
FOR("statement")
+ LPAR
+ pp.Optional(expr)
+ SEMI
+ expr
+ SEMI
+ pp.Optional(expr)
+ RPAR
+ stmt
)
while_stmt = pp.Group(WHILE("statement") + LPAR + expr + RPAR + stmt)
if_stmt = pp.Group(
IF("statement")
+ LPAR
+ pp.Group(expr)("condition")
+ RPAR
+ pp.Group(stmt)("then_statement")
+ pp.Group(pp.Optional(ELSE + stmt))("else_statement")
)
stmt_block = pp.Group(
LBRACE + pp.ZeroOrMore(variable_decl) + pp.ZeroOrMore(stmt) + RBRACE
)
stmt <<= (
if_stmt
| while_stmt
| for_stmt
| break_stmt
| return_stmt
| print_stmt
| stmt_block
| pp.Group(expr + SEMI)
)
formals = pp.Optional(pp.delimitedList(variable))
prototype = pp.Group(
(type_ | VOID)("return_type")
+ ident("function_name")
+ LPAR
+ formals("args")
+ RPAR
+ SEMI
)("prototype")
function_decl = pp.Group(
(type_ | VOID)("return_type")
+ ident("function_name")
+ LPAR
+ formals("args")
+ RPAR
+ stmt_block("body")
)("function_decl")
interface_decl = pp.Group(
INTERFACE
+ ident("interface_name")
+ LBRACE
+ pp.ZeroOrMore(prototype)("prototypes")
+ RBRACE
)("interface")
field = variable_decl | function_decl
class_decl = pp.Group(
CLASS
+ ident("class_name")
+ pp.Optional(EXTENDS + ident)("extends")
+ pp.Optional(IMPLEMENTS + pp.delimitedList(ident))("implements")
+ LBRACE
+ pp.ZeroOrMore(field)("fields")
+ RBRACE
)("class_decl")
decl = variable_decl | function_decl | class_decl | interface_decl | prototype
program = pp.OneOrMore(pp.Group(decl))
decaf_parser = program
stmt.runTests(
"""\
sin(30);
a = 1;
b = 1 + 1;
b = 1 != 2 && false;
print("A");
a.b = 100;
a.b = 100.0;
a[100] = b;
a[0][0] = 2;
a = 0x1234;
"""
)
test_program = """
void getenv(string var);
int main(string[] args) {
if (a > 100) {
Print(a, " is too big");
} else if (a < 100) {
Print(a, " is too small");
} else {
Print(a, "just right!");
}
}
"""
print(decaf_parser.parseString(test_program).dump())