Grammar Rules for @code{rpcalc}
-* Rpcalc Input::
-* Rpcalc Line::
-* Rpcalc Expr::
+* Rpcalc Input:: Explanation of the @code{input} nonterminal
+* Rpcalc Line:: Explanation of the @code{line} nonterminal
+* Rpcalc Expr:: Explanation of the @code{expr} nonterminal
Location Tracking Calculator: @code{ltcalc}
* Mfcalc Declarations:: Bison declarations for multi-function calculator.
* Mfcalc Rules:: Grammar rules for the calculator.
* Mfcalc Symbol Table:: Symbol table management subroutines.
+* Mfcalc Lexer:: The lexical analyzer.
+* Mfcalc Main:: The controlling function.
Bison Grammar Files
Here are the C and Bison declarations for the reverse polish notation
calculator. As in C, comments are placed between @samp{/*@dots{}*/}.
+@comment file: rpcalc.y
@example
/* Reverse polish notation calculator. */
%@{
#define YYSTYPE double
+ #include <stdio.h>
#include <math.h>
int yylex (void);
void yyerror (char const *);
Here are the grammar rules for the reverse polish notation calculator.
+@comment file: rpcalc.y
@example
input: /* empty */
| input line
;
line: '\n'
- | exp '\n' @{ printf ("\t%.10g\n", $1); @}
+ | exp '\n' @{ printf ("%.10g\n", $1); @}
;
exp: NUM @{ $$ = $1; @}
rule are referred to as @code{$1}, @code{$2}, and so on.
@menu
-* Rpcalc Input::
-* Rpcalc Line::
-* Rpcalc Expr::
+* Rpcalc Input:: Explanation of the @code{input} nonterminal
+* Rpcalc Line:: Explanation of the @code{line} nonterminal
+* Rpcalc Expr:: Explanation of the @code{expr} nonterminal
@end menu
@node Rpcalc Input
@example
line: '\n'
- | exp '\n' @{ printf ("\t%.10g\n", $1); @}
+ | exp '\n' @{ printf ("%.10g\n", $1); @}
;
@end example
Here is the code for the lexical analyzer:
+@comment file: rpcalc.y
@example
@group
/* The lexical analyzer returns a double floating point
kept to the bare minimum. The only requirement is that it call
@code{yyparse} to start the process of parsing.
+@comment file: rpcalc.y
@example
@group
int
@code{yyerror} (@pxref{Interface, ,Parser C-Language Interface}), so
here is the definition we will use:
+@comment file: rpcalc.y
@example
@group
#include <stdio.h>
@example
$ @kbd{rpcalc}
@kbd{4 9 +}
-13
+@result{} 13
@kbd{3 7 + 3 4 5 *+-}
--13
+@result{} -13
@kbd{3 7 + 3 4 5 * + - n} @r{Note the unary minus, @samp{n}}
-13
+@result{} 13
@kbd{5 6 / 4 n +}
--3.166666667
+@result{} -3.166666667
@kbd{3 4 ^} @r{Exponentiation}
-81
+@result{} 81
@kbd{^D} @r{End-of-file indicator}
$
@end example
@example
$ @kbd{mfcalc}
@kbd{pi = 3.141592653589}
-3.1415926536
+@result{} 3.1415926536
@kbd{sin(pi)}
-0.0000000000
+@result{} 0.0000000000
@kbd{alpha = beta1 = 2.3}
-2.3000000000
+@result{} 2.3000000000
@kbd{alpha}
-2.3000000000
+@result{} 2.3000000000
@kbd{ln(alpha)}
-0.8329091229
+@result{} 0.8329091229
@kbd{exp(ln(beta1))}
-2.3000000000
+@result{} 2.3000000000
$
@end example
* Mfcalc Declarations:: Bison declarations for multi-function calculator.
* Mfcalc Rules:: Grammar rules for the calculator.
* Mfcalc Symbol Table:: Symbol table management subroutines.
+* Mfcalc Lexer:: The lexical analyzer.
+* Mfcalc Main:: The controlling function.
@end menu
@node Mfcalc Declarations
Here are the C and Bison declarations for the multi-function calculator.
+@comment file: mfcalc.y
@smallexample
@group
%@{
- #include <math.h> /* For math functions, cos(), sin(), etc. */
- #include "calc.h" /* Contains definition of `symrec'. */
+ #include <stdio.h> /* For printf, etc. */
+ #include <math.h> /* For pow, used in the grammar. */
+ #include "calc.h" /* Contains definition of `symrec'. */
int yylex (void);
void yyerror (char const *);
%@}
Most of them are copied directly from @code{calc}; three rules,
those which mention @code{VAR} or @code{FNCT}, are new.
+@comment file: mfcalc.y
@smallexample
@group
input: /* empty */
@group
line:
'\n'
- | exp '\n' @{ printf ("\t%.10g\n", $1); @}
- | error '\n' @{ yyerrok; @}
+ | exp '\n' @{ printf ("%.10g\n", $1); @}
+ | error '\n' @{ yyerrok; @}
;
@end group
definition, which is kept in the header @file{calc.h}, is as follows. It
provides for either functions or variables to be placed in the table.
+@comment file: calc.h
@smallexample
@group
/* Function type. */
@end group
@end smallexample
-The new version of @code{main} includes a call to @code{init_table}, a
-function that initializes the symbol table. Here it is, and
-@code{init_table} as well:
+The new version of @code{main} will call @code{init_table} to initialize
+the symbol table:
+@comment file: mfcalc.y
@smallexample
-#include <stdio.h>
-
-@group
-/* Called by yyparse on error. */
-void
-yyerror (char const *s)
-@{
- printf ("%s\n", s);
-@}
-@end group
-
@group
struct init
@{
@group
struct init const arith_fncts[] =
@{
- "sin", sin,
- "cos", cos,
- "atan", atan,
- "ln", log,
- "exp", exp,
- "sqrt", sqrt,
- 0, 0
+ @{ "atan", atan @},
+ @{ "cos", cos @},
+ @{ "exp", exp @},
+ @{ "ln", log @},
+ @{ "sin", sin @},
+ @{ "sqrt", sqrt @},
+ @{ 0, 0 @},
@};
@end group
@group
/* Put arithmetic functions in table. */
+static
void
init_table (void)
@{
@}
@}
@end group
-
-@group
-int
-main (void)
-@{
- init_table ();
- return yyparse ();
-@}
-@end group
@end smallexample
By simply editing the initialization list and adding the necessary include
The function @code{getsym} is passed the name of the symbol to look up. If
found, a pointer to that symbol is returned; otherwise zero is returned.
+@comment file: mfcalc.y
@smallexample
+#include <stdlib.h> /* malloc. */
+#include <string.h> /* strlen. */
+
symrec *
putsym (char const *sym_name, int sym_type)
@{
@}
@end smallexample
+@node Mfcalc Lexer
+@subsection The @code{mfcalc} Lexer
+
The function @code{yylex} must now recognize variables, numeric values, and
the single-character arithmetic operators. Strings of alphanumeric
characters with a leading letter are recognized as either variables or
No change is needed in the handling of numeric values and arithmetic
operators in @code{yylex}.
+@comment file: mfcalc.y
@smallexample
@group
#include <ctype.h>
/* Initially make the buffer long enough
for a 40-character symbol name. */
if (length == 0)
- length = 40, symbuf = (char *)malloc (length + 1);
+ @{
+ length = 40;
+ symbuf = (char *) malloc (length + 1);
+ @}
i = 0;
do
@end group
@end smallexample
+@node Mfcalc Main
+@subsection The @code{mfcalc} Main
+
+The error reporting function is unchanged, and the new version of
+@code{main} includes a call to @code{init_table}:
+
+@comment file: mfcalc.y
+@smallexample
+
+@group
+@group
+/* Called by yyparse on error. */
+void
+yyerror (char const *s)
+@{
+ fprintf (stderr, "%s\n", s);
+@}
+@end group
+
+int
+main (int argc, char const* argv[])
+@{
+ init_table ();
+ return yyparse ();
+@}
+@end group
+@end smallexample
+
This program is both powerful and flexible. You may easily add new
functions, and it is a simple job to modify this code to install
predefined variables such as @code{pi} or @code{e} as well.
bracketed syntax @code{$[name]} and @code{@@[name]} must be used:
@example
@group
-if-stmt: IF '(' expr ')' THEN then.stmt ';'
+if-stmt: "if" '(' expr ')' "then" then.stmt ';'
@{ $[if-stmt] = new_if_stmt ($expr, $[then.stmt]); @}
@end group
@end example
else if (!(yyin = fopen (file.c_str (), "r")))
@{
error (std::string ("cannot open ") + file + ": " + strerror(errno));
- exit (1);
+ exit (EXIT_FAILURE);
@}
@}
{
yyin = fopen (file, "r");
if (!yyin)
- exit (2);
+ {
+ perror ("fopen");
+ exit (EXIT_FAILURE);
+ }
/* One token only. */
yylex ();
if (fclose (yyin) != 0)
- exit (3);
+ {
+ perror ("fclose");
+ exit (EXIT_FAILURE);
+ }
return 0;
}
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