Шрифт:
.ix [hoc] arguments
.IT $3
refers to the third (1-indexed) argument.
They are passed by value and within functions
are semantically equivalent to variables.
It is an error to refer to an argument numbered greater than the
number of arguments passed to the routine. The error checking
is done dynamically, however, so a routine may have variable numbers
of arguments if initial arguments affect the number of arguments
to be referenced (as in C's @printf@).
.PP
Functions and procedures may recurse, but the stack has limited depth
(about a hundred calls). The following shows a
.I
hoc
definition of Ackermann's function:
.ix Ackermann's~function
.DS
.ft CW
.ix [ack]~function
.S $ "hoc
.S "func ack {
.S " if ($1 == 0) return $2+1
.S " if ($2 == 0) return ack($1-1, 1)
.S " return ack($1-1, ack($1, $2-1))
.S "}
.S "ack(3, 2)
29
.S "ack(3, 3)
61
.S "ack(3, 4)
hoc: stack too deep near line 8
\&...
.ft
.DE
.bp
.NH
Examples
.PP
Stirling's~formula:
.ix Stirling's~formula
.EQ
n! ~\(ap~ sqrt {2n pi} (n/e) sup n (1+ 1 over 12n )
.EN
.DS
.ft CW
.S $ hoc
.S "func stirl {
.S " return sqrt(2*$1*PI) * ($1/E)"$1*(1 + 1/(12*$1)) .S "}
.S "stirl(10)
3628684.7
.S stirl(20)
2.4328818e+18
.ft R
.DE
.PP
Factorial function, @n!@:
.ix [fac]~function
.DS
. S "func fac if ($1 <= 0) return 1 else return $1 * fac($1-1)
.ft R
.DE
.PP
Ratio of factorial to Stirling approximation:
.DS
.S "i = 9
.S "while ((i = i+1) <= 20) {
.S \ \ \ \ \ \ \ \ print\ i,\ "\ \ ",\ fac(i)/stirl(i),\ "\en"
.S "} .ft CW
10 1.0000318
11 1.0000265
12 1.0000224
13 1.0000192
14 1.0000166
15 1.0000146
16 1.0000128
17 1.0000114
18 1.0000102
19 1.0000092
20 1.0000083
.ft
.DE
3.7.14
hoc.y
%{
#include "hoc.h"
#define code2(c1,c2) code(c1); code(c2)
#define code3(c1,c2,c3) code(c1); code(c2); code(c3)
%}
%union {
Symbol *sym; /* symbol table pointer */
Inst *inst; /* machine instruction */
int narg; /* number of arguments */
}
%token <sym> NUMBER STRING PRINT VAR BLTIN UNDEF WHILE IF ELSE
%token <sym> FUNCTION PROCEDURE RETURN FUNC PROC READ