CS360: Mini Language. Michael Conway Original slides by Mark Boady. March 11, 2015

Transcription

1 CS360: Mini Language Michael Conway Original slides by Mark Boady March 11, 2015

2 Mini language A simple programming language Implemented in PLY You will modify it for PA4

3 Grammar At the top level, we dene a program program -> stmt_list stmt_list -> stmt SEMICOLON stmt_list stmt stmt -> assign_stmt while_stmt if_stmt define_stmt

4 Grammar What kind of statements can be used to write a program? assign_stmt -> INDENT ASSIGNOP expr while_stmt -> WHILE expr DO stmt_list OD if_stmt -> IF expr THEN stmt_list ELSE stmt_list FI define_stmt -> DEFINE IDENT PROC LPAREN param_list RPAREN stmt_list END

5 Grammar Expressions are commands that can actually be evaluated expr -> expr PLUS term term expr -> expr MINUS term term term -> term TIMES fact fact fact -> NUMBER ( expr ) IDENT func_call Basic Elements are numbers or Variable Names Number -> [0-9]+ Ident -> [a-z]+ except reserved words

6 Grammar Function calls and denitions need inputs func_call -> IDENT LPAREN expr_list RPAREN expr_list -> expr COMMA expr_list expr param_list -> IDENT COMMA param_list IDENT

7 Parsing Instead of evaluating as we parse Step 1: Build a Parse Tree Step 2: Evaluate the Parse Tree def p_add( p ) : 'expr : expr PLUS term' p[0] = Plus( p[1], p[3] ) def p_assn( p ) : 'assign_stmt : IDENT ASSIGNOP expr' p[0] = AssignStmt( p[1], p[3] )

8 Parse Tree Parse Tree Objects Constructor Creates a Tree eval walks the tree and evaluates the expression Display is for debugging class Plus( Expr ) : def init ( self, lhs, rhs ) : self.lhs = lhs self.rhs = rhs def eval( self, nt, ft ) : return (self.lhs.eval( nt, ft ) + self.rhs.eval( nt, ft )) def display( self, nt, ft, depth=0 ) :...

9 Evaluating Evaluating the Parse Tree def eval( self, nt, ft ) : return (self.lhs.eval( nt, ft ) + self.rhs.eval( nt, ft )) nt - The name table, stores the names of variables and values ft - function table, stores the dened functions

10 Parse Tree Parse Tree for a := 4 * 7; b := a+5

11 Parse Tree Parse Tree for a := 4 * 7; b := a+5

12 Parse Tree Parse Tree for a := 4 * 7; b := a+5

13 Parse Tree Parse Tree for a := 4 * 7; b := a+5

14 Decorating the Tree Parse Tree for a := 4 * 7; b := a+5

15 Decorating the Tree Parse Tree for a := 4 * 7; b := a+5

16 Decorating the Tree Parse Tree for a := 4 * 7; b := a+5

17 Decorating the Tree Parse Tree for a := 4 * 7; b := a+5

18 Decorating the Tree Decorating the parse tree evaluates an expression In the Mini Language, we use the eval(nt,ft) function for this The Mini Language is interpreted, it parses straight to a result We can also use the parse tree to compile Now we see how the code could be decorated with assembly code

19 Decorating the Tree (ver. 2) Parse Tree for a := 4 * 7; b := a+5

20 Decorating the Tree (ver. 2) Parse Tree for a := 4 * 7; b := a+5

21 Decorating the Tree (ver. 2) Parse Tree for a := 4 * 7; b := a+5

22 Assembly Code Note: If you used g++ it would make 4*7 a constant 28. Ltmp4:.cfi_def_cfa_register %rbp movl $0, %eax movl $4, -4(%rbp) movl $7, -8(%rbp) movl -4(%rbp), %ecx imull -8(%rbp), %ecx movl %ecx, -12(%rbp) movl $5, -16(%rbp) movl -12(%rbp), %ecx addl -16(%rbp), %ecx movl %ecx, -20(%rbp) popq %rbp ret.cfi_endproc

23 An Example Program A program to nd the factorial of n n := 0-5; if n then i := n else i := 0 - n fi; fact := 1; while i do fact := fact * i; i := i - 1 od For while and if, false means <=0 and true means >0

24 Running a Program $ python interpreterext.py < TestInput/fact.p [42] Running Program Dump of Symbol Table Name Table i -> 0 fact -> 120 n -> -5 Function Table The program has no print command We can see the nal symbol table and look for answers

25 PA4 Mini Language Question of PA4 Add the comparison operators: < > <= >= ==!= Currently: true means > 0 false means <= 0 You can make the operators return 0 or 1 (4 < 5) returns 1 for true (5 == 7) return 0 for false

26 PA4 Add Lists expr : list_stuff list_stuff : LBRACKET expr_list RBRACKET list_stuff : LBRACKET RBRACKET list_stuff : CAR expr list_stuff : CDR expr list_stuff : CONS expr COMMA expr list_stuff : NULL expr

27 PA4 Problem 2 Base it on your code from PA3 Problem 3 Redo Problem 3 of PA2 in SICP Query Language Read the SICP Book You can base on the address database we saw in lab 4

28 Lab 6 Part 1: Add Exponent to Recursive Descent Parser Part 2: Complete Recursive Descent Parse for Reg Expr Part 3: Test the Mini Language

29 Lab 6 def expr(self): result=self.term() while self.token == '+': self.match('+',"+ expected") result +=self.term() return result def term(self): result = self.factor() while self.token == '*': self.match('*',"* Expected") result *= self.factor() return result

30 Lab 6 def factor(self): if self.token=="(": self.match("(","( Expected") result = self.expr() self.match(")",") Expected") else: result = self.number() return result def number(self): mystr="" while self.token.isdigit(): mystr+=self.token self.gettoken() return int(mystr)

31 Concat No Character to match on! def concat(self): #concat -> closure { closure} result = self.closure() while What do I match on: Do I need to match anything? result = RegConcat(result,self.closure()) return result What can be after the concat? letters a-z or a left parenthesis What can't be after concat? *,,), newline