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1 line
9.5 KiB
C
1 line
9.5 KiB
C
#
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/*
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Copyright (C) 1976
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by the
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Board of Trustees
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of the
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University of Illinois
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All rights reserved
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FILE NAME:
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parse.c
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PURPOSE:
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Contains the routines which keep track of the parse stack.
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GLOBALS:
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p_stack = The parse stack, set by both routines
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il = Stack of indentation levels, set by parse
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cstk = Stack of case statement indentation levels, set by parse
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tos = Pointer to top of stack, set by both routines.
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FUNCTIONS:
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parse
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reduce
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*/
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/*
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Copyright (C) 1976
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by the
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Board of Trustees
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of the
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University of Illinois
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All rights reserved
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NAME:
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parse
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FUNCTION:
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Parse is given one input which is a "maxi token" just scanned from
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input. Maxi tokens are signifigant constructs such as else, {, do,
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if (...), etc. Parse works with reduce to maintain a parse stack
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of these constructs. Parse is responsible for the "shift" portion
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of the parse algorithm, and reduce handles the "reduce" portion.
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ALGORITHM:
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1) If there is "ifstmt" on the stack and input is anything other than
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an else, then change the top of stack (TOS) to <stmt>. Do a reduce.
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2) Use a switch statement to implement the following shift operations:
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TOS___ Input_____ Stack_____ Note____
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decl decl nothing
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anything else decl decl
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"dostmt" while (..) Change TOS to <stmt>
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anything else while (..) while
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"ifstmt" else Change TOS to "ifelse"
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{ <stmtl> } Change { <stmtl>
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to <stmtl>
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switch (..) switch
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do do
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for(..) for
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; <stmt>
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{ { <stmt>
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PARAMETERS:
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tk An integer code for the maxi token scanned
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RETURNS:
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Nothing
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GLOBALS:
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break_comma = Set to true when in a declaration but not initialization
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btype_2
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case_ind =
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cstk =
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i_l_follow =
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il = Stack of indentation levels
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ind_level =
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p_stack = Stack of token codes
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search_brace = Set to true if we must look for possibility of moving a
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brace
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tos = Pointer to top of p_stack, il, and cstk
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CALLS:
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printf (lib)
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reduce
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CALLED BY:
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main
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HISTORY:
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initial coding November 1976 D A Willcox of CAC
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*/
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#include "indntglo.h";
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#include "indntcod.h";
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int p_stack[50] = stmt;
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/* this is the parser's stack */
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int il[50]; /* this stack stores indentation levels */
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int cstk[50]; /* used to store case stmt indentation levels */
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int tos = 0; /* pointer to top of stack */
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parse (tk)
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int tk; /* the code for the construct scanned */
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{
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int i;
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#ifdef debug
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printf ("%2d - %s\n", tk, token);
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#endif
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while (p_stack[tos] == ifhead && tk != elselit) {
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/* true if we have an if without an else */
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p_stack[tos] = stmt; /* apply the if(..) stmt ::= stmt reduction */
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reduce (); /* see if this allows any reduction */
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}
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switch (tk) { /* go on and figure out what to do with the
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input */
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case decl: /* scanned a declaration word */
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search_brace = btype_2;
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/* indicate that following brace should be on same line */
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if (p_stack[tos] != decl) {
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/* only put one declaration onto stack */
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break_comma = true;
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/* while in declaration, newline should be forced after comma */
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p_stack[++tos] = decl;
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il[tos] = i_l_follow;
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if (ljust_decl) {
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/* only do if we want left justified declarations */
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ind_level = 0;
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for (i = tos - 1; i > 0; --i)
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if (p_stack[i] == decl)
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++ind_level;
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/* indentation is number of declaration levels deep we are */
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i_l_follow = ind_level;
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}
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}
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break;
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case ifstmt: /* scanned if (...) */
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case dolit: /* 'do' */
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case forstmt: /* for (...) */
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p_stack[++tos] = tk;
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il[tos] = ind_level = i_l_follow;
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++i_l_follow; /* subsequent statements should be indented 1 */
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search_brace = btype_2;
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break;
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case lbrace: /* scanned { */
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break_comma = false;
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/* don't break comma in an initial list */
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if (p_stack[tos] == stmt || p_stack[tos] == decl
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|| p_stack[tos] == stmtl)
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++i_l_follow; /* it is a random, isolated stmt group or a
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declaration */
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else {
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if (s_code == e_code) {
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/* only do this if there is nothing on the line */
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--ind_level;
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/* it is a group as part of a while, for, etc. */
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if (p_stack[tos] == swstmt)
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--ind_level;
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/* for a switch, brace should be two levels out from the code
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*/
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}
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}
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p_stack[++tos] = lbrace;
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il[tos] = ind_level;
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p_stack[++tos] = stmt;
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/* allow null stmt between braces */
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il[tos] = i_l_follow;
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break;
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case whilestmt: /* scanned while (...) */
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if (p_stack[tos] == dohead) {
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/* it is matched with do stmt */
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ind_level = i_l_follow = il[tos];
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p_stack[++tos] = whilestmt;
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il[tos] = ind_level = i_l_follow;
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}
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else { /* it is a while loop */
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p_stack[++tos] = whilestmt;
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il[tos] = i_l_follow;
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++i_l_follow;
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search_brace = btype_2;
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}
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break;
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case elselit: /* scanned an else */
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if (p_stack[tos] != ifhead) {
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printf ("%d: Unmatched else\n", line_no);
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}
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else {
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ind_level = il[tos];
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/* indentation for else should be same as for if */
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i_l_follow = ind_level + 1;
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/* everything following should be in 1 level */
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p_stack[tos] = elsehead;
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/* remember if with else */
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search_brace = btype_2;
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}
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break;
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case rbrace: /* scanned a } */
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/* stack should have <lbrace> <stmt> or <lbrace> <stmtl> */
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if (p_stack[tos - 1] == lbrace) {
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ind_level = i_l_follow = il[--tos];
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p_stack[tos] = stmt;
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}
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else {
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printf ("%d: Stmt nesting error\n", line_no);
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}
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break;
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case swstmt: /* had switch (...) */
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p_stack[++tos] = swstmt;
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cstk[tos] = case_ind;
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/* save current case indent level */
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il[tos] = i_l_follow;
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case_ind = i_l_follow + 1;
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/* cases should be one level down from switch */
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i_l_follow += 2; /* statements should be two levels in */
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search_brace = btype_2;
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break;
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case semicolon: /* this indicates a simple stmt */
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break_comma = false;
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/* turn off flag to break after commas in a declaration */
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p_stack[++tos] = stmt;
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il[tos] = ind_level;
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break;
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default: /* this is an error */
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printf ("%d: Unknown code to parser - %d\n", line_no, tk);
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return;
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} /* end of switch */
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reduce (); /* see if any reduction can be done */
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#ifdef debug
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for (i = 1; i <= tos; ++i)
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printf ("(%d %d)", p_stack[i], il[i]);
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printf ("\n");
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#endif
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return;
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}
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/*
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Copyright (C) 1976
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by the
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Board of Trustees
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of the
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University of Illinois
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All rights reserved
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NAME:
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reduce
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FUNCTION:
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Implements the reduce part of the parsing algorithm
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ALGORITHM:
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The following reductions are done. Reductions are repeated until no
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more are possible.
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Old___ TOS___ New___ TOS___
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<stmt> <stmt> <stmtl>
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<stmtl> <stmt> <stmtl>
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do <stmt> "dostmt"
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if <stmt> "ifstmt"
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switch <stmt> <stmt>
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decl <stmt> <stmt>
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"ifelse" <stmt> <stmt>
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for <stmt> <stmt>
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while <stmt> <stmt>
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"dostmt" while <stmt>
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On each reduction, i_l_follow (the indentation for the following line)
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is set to the indentation level associated with the old TOS.
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PARAMETERS:
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None
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RETURNS:
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Nothing
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GLOBALS:
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cstk
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i_l_follow =
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il
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p_stack =
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tos =
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CALLS:
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None
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CALLED BY:
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parse
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HISTORY:
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initial coding November 1976 D A Willcox of CAC
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*/
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/*----------------------------------------------*\
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| REDUCTION PHASE
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\*----------------------------------------------*/
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reduce () {
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register int i;
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/* local looping variable */
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for (;;) { /* keep looping until there is nothing left to
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reduce */
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switch (p_stack[tos]) {
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case stmt:
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switch (p_stack[tos - 1]) {
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case stmt:
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case stmtl:
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/* stmtl stmt or stmt stmt */
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p_stack[--tos] = stmtl;
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break;
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case dolit:
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/* <do> <stmt> */
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p_stack[--tos] = dohead;
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i_l_follow = il[tos];
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break;
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case ifstmt:
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/* <if> <stmt> */
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p_stack[--tos] = ifhead;
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for (i = tos - 1;
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(
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p_stack[i] != stmt
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&&
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p_stack[i] != stmtl
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&&
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p_stack[i] != lbrace
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);
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--i);
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i_l_follow = il[i];
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/* for the time being, we will assume that there is no else
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on this if, and set the indentation level accordingly.
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If an else is scanned, it will be fixed up later */
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break;
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case swstmt:
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/* <switch> <stmt> */
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case_ind = cstk[tos - 1];
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case decl: /* finish of a declaration */
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case elsehead:
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/* <<if> <stmt> else> <stmt> */
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case forstmt:
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/* <for> <stmt> */
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case whilestmt:
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/* <while> <stmt> */
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p_stack[--tos] = stmt;
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i_l_follow = il[tos];
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break;
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default: /* <anything else> <stmt> */
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return;
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} /* end of section for <stmt> on top of stack */
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break;
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case whilestmt: /* while (...) on top */
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if (p_stack[tos - 1] == dohead) {
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/* it is termination of a do while */
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p_stack[--tos] = stmt;
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break;
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}
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else
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return;
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default: /* anything else on top */
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return;
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} /* end of big switch */
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} /* end of reduction phase for (;;) */
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}
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