Chapter 2-2 A Simple One-Pass Compiler

Syntax-directed translation Syntax-directed definition  translation of a construct in terms of attributes associated with its syntactic components Syntactic structure :: context-free grammar Grammar symbol :: a set of attributes and with each production, a set of semantic rules for computing values of the attributes associated with the symbols appearing in the production Translation  input-output mapping Annotated parse tree  a parse tree showing the attribute values at each node

Synthesized Attributes An attribute is said to be synthesized if its value at a parse-tree node is determined from attribute values at the children of node 예제 설명

Syntax-directed definition for infix to postfix translation. PRODUCTION SEMANTIC RULE expr  expr1 + term expr  expr1 - term expr  term term  0 term  1 . . . term  9 expr.t := expr1.t || term.t || ‘+’ expr.t := expr1.t || term.t || ‘-’ expr.t := term.t term.t := ‘0’ term.t := ‘1’ term.t := ‘9’ Syntax-directed definition for infix to postfix translation.

Attribute values at nodes in a parse tree.

Depth first traversals Robot positioning :: seq  seq instr | begin instr  east | north | west | south Depth-first traversals Translation Schemes Context-free grammar in which program fragments called semantic actions are embedded Emitting a Translation

Annotated parse tree for begin west south.

Syntax-directed definition of the robot’s position. PRODUCTION SEMANTIC RULES seq  begin seq.x := 0 seq.y := 0 seq  seq1 instr seq.x := seq.x1 + instr.dx seq.y := seq.y1 + instr.dy instr  east instr.dx := 1 instr.dy := 0 instr  north instr.dx := 0 instr.dy := 1 instr  west instr.dx := -1 instr  south instr.dy := -1 Syntax-directed definition of the robot’s position.

Actions translating expressions into postfix notation. expr  expr1 + term expr  expr1 - term expr  term term  0 term  1 . . . term  9 { print (‘+’) } { print (‘-’) } { print (‘0’) } { print (‘1’) } { print (‘9’) } Actions translating expressions into postfix notation.

Actions translating 9-5+2 into 95-2+

Top-down parsing Lookahead … the current token being scanned Array[ num dotdot num ] of integer 과정 설명

type  simple |  id | array [ simple ] of type Simple  integer | char | num dotdot num (2.8)

Steps in the top-down construction of a parse tree (a) type type Array [ simple ] of type (c) Array [ simple ] of type num dotdot num (d) Array [ simple ] of type num dotdot num simple (e) Array [ simple ] of type num dotdot num simple integer Steps in the top-down construction of a parse tree

Predictive parsing First Designing a Predictive Parser Left Recursion 예제로 설명 ∈-production Designing a Predictive Parser Left Recursion expr  expr + term 일반화

expr  term rest rest  + term { print(‘+’) } rest | - term { print(‘-’) } rest | term  0 { print (‘0’) } term  1 { print (‘1’) } . . . term  9 { print (‘9’) } (2.14)

Translation of 9 – 5 + 2 into 95 – 2 +. expr term rest 9 {print(‘9’)} - term {print(‘-’)} rest 5 {print(‘5’)} + term {print(‘+’)} rest 2 {print(‘2’)} Translation of 9 – 5 + 2 into 95 – 2 +.

Fig. 2. 22. Functions for the nonterminals expr, rest, and term. { term(); rest(); } rest() if(lookahead == ‘+’) { match(‘+’); term(); putchar(‘+’); rest(); else if (lookahead == ‘-’) { match(‘-’); term(); putchar(‘-’); rest(); else; term() if (isdigit(lookahead)) { putchar(lookahead); match(lookahead); else error; Fig. 2. 22. Functions for the nonterminals expr, rest, and term.

Replacement for functions expr and rest of Fig. 2.22. { term(); while(1) if(lookahead == ‘+’) { match(‘+’); term(); putchar(‘+’); } else if (lookahead == ‘-’) { match(‘-’); term(); putchar(‘-’); else break; Replacement for functions expr and rest of Fig. 2.22.

Implementing the interactions in Fig. 2. 25. uses getchar() return token to read character to caller pushes back c using ungetc(c, stdin) sets global variable to attribute value lexan() lexical analyzer tokenval Implementing the interactions in Fig. 2. 25.

Symbol table and array for storing strings.

Code layout for conditional and while statements. stmt  if expr then stmt1 { out := newlable; stmt.t := expr.t || ‘gofalse’ out || stmt1.t || ‘label’ out (2.18) IF WHILE label test code for expr gofalse out code for stmt1 goto test label out code for expr gofalse out code for stmt1 label out Code layout for conditional and while statements.

Fig. 4.15. Parsing table M for grammar (4.11) NONTER-MINAL INPUT SYMBOL id + * ( ) $ E E' T T' F E  TE' T  FT' F  id E'  +TE' T'   T'  *FT' F  (E) E'   Fig. 4.15. Parsing table M for grammar (4.11)