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 }

 print($1)

}

double(1024)

3.7.5 fac

func fac() {

 if ($1 <= 0) return 1 else return $1 * fac($1-1)

}

3.7.6 fac1

func fac() if ($1 <= 0) return 1 else return $1 * fac($1-1)

fac(0)

fac(7)

fac(10)

3.7.7 fac2

func fac() {

 if ($1 <= 0) {

  return 1

 }

 return $1 * fac($1-1)

}

i=0

while(i<=20){

 print "factorial of ", i, "is ", fac(i), "n"

 i=i+1

}

3.7.8 fib

proc fib() {

 a = 0

 b = 1

 while (b < $1) {

  print b

  c = b

  b = a+b

  a = c

 }

 print "n"

}

3.7.9 fib2

{

 n=0

 a=0

 b=1

 while(b<10000000){

  n=n+1

  c=b

  b=a+b

  a=c

  print(b)

 }

 print(n)

}

3.7.10 fibsum

proc fib(){

 a=1

 b=1

 c=2

 d=3

 sum = a+b+c+d

 while(d<$1){

  e=d+c

  print(e)

  a=b

  b=c

  c=d

  d=e

  sum=sum+e

 }

 print(sum)

}

fib(1000)

3.7.11 fibtest

proc fib() {

 a = 0

 b = 1

 while (b < $1) {

  c = b

  b = a+b

  a = c

 }

}

i = 1

while (i < 1000) {

 fib(1000)

 i = i + 1

}

3.7.12 hoc.h

typedef struct Symbol { /* symbol table entry */

 char *name;

 short type;

 union {

  double val; /* VAR */

  double (*ptr)(); /* BLTIN */

  int (*defn)(); /* FUNCTION, PROCEDURE */

  char *str; /* STRING */

 } u;

 struct Symbol *next; /* to link to another */

} Symbol;

Symbol *install(), *lookup();

typedef union Datum { /* interpreter stack type */

 double val;

 Symbol *sym;

} Datum;

extern Datum pop();

extern eval(), add(), sub(), mul(), div(), negate(), power();

typedef int (*Inst)();

#define STOP (Inst)0

extern Inst *progp, *progbase, prog[], *code();

extern assign(), bltin(), varpush(), constpush(), print(), varread();

extern prexpr(), prstr();

extern gt(), lt(), eq(), ge(), le(), ne(), and(), or(), not();

extern ifcode(), whilecode(), call(), arg(), argassign();

extern funcret(), procret();

3.7.13 hoc.ms

.EQ

delim @@

.EN

.TL

Hoc - An Interactive Language For Floating Point Arithmetic

.AU

Brian Kernighan

Rob Pike

.AB

.I Hoc

is a simple programmable interpreter

for floating point expressions.

It has C-style control flow,

function definition and the usual

numerical built-in functions such as cosine and logarithm.

.AE

.NH

Expressions

.PP

.I Hoc

is an expression language,

much like C:

although there are several control-flow statements,

most statements such as assignments

are expressions whose value is disregarded.

For example, the assignment operator

= assigns the value of its right operand

to its left operand, and yields the value,

so multiple assignments work.

The expression grammar is:

.DS

.I

expr: number

 | variable

 | ( expr )

 | expr binop expr

 | unop expr

 | function ( arguments )

.R

.DE

Numbers are floating point.

The input format is

that recognized by @[email protected](3):

.ix [scanf]

digits, decimal point, digits,

.ix [hoc] manual

.ix assignment expression

.ix multiple assignment

@[email protected] or @[email protected], signed exponent.

At least one digit or a decimal point

must be present;

the other components are optional.

.PP

Variable names are formed from a letter

followed by a string of letters and numbers,

@[email protected] refers to binary operators such

as addition or logical comparison;

@[email protected] refers to the two negation operators,

'!' (logical negation, 'not')

and '-' (arithmetic negation, sign change).

Table 1 lists the operators.

.TS

center, box;

с s

lfCW l.

fBTable 1:fP Operators, in decreasing order of precedence

.sp .5

^       exponentiation (s-1FORTRANs0 **), right associative

! -    (unary) logical and arithmetic negation

* /     multiplication, division

+ -    addition, subtraction

> >=    relational operators: greater, greater or equal,

< <=    less, less or equal,

&== != equal, not equal (all same precedence)

&&      logical AND (both operands always evaluated)

||      logical OR (both operands always evaluated)

&=     assignment, right associative

.ТЕ

.ix table~of [hoc] operators

.PP

Functions, as described later, may be defined by the user.

Function arguments are expressions separated by commas.

There are also a number of built-in functions,

all of which take a single argument,

described in Table 2.

.TS

center, box;

с s

lfCW l.

fBTable 2:fP Built-in Functions

.sp .5

abs(x)   @| x |@, absolute value of @[email protected]

atan(x)  arc tangent of @[email protected]

cos(x)   @cos (x)@, cosine of @[email protected]

exp(x)   @e sup [email protected], exponential of @[email protected]

int(x)   integer part of @[email protected], truncated towards zero

log(x)   @log (x)@, logarithm base @[email protected] of @[email protected]

log10(x) @log sub 10 (x)@, logarithm base 10 of @[email protected]

sin(x)   @sin (x)@, sine of @[email protected]

sqrt(x)  @sqrt [email protected], @x sup [email protected]

.ТЕ

.ix table~of [hoc] functions

.PP

Logical expressions have value 1.0 (true) and 0.0 (false).

As in C,

any non-zero value is taken to be true.

As is always the case with floating point numbers,

equality comparisons are inherently suspect. .PP

.I Hoc

also has a few built-in constants, shown in Table 3.

.TS

center, box;

c s s

lfCW n l.

fBTable 3:fP Built-in Constants

.sp .5

DEG   57.29577951308232087680 @180/ [email protected], degrees per radian

E     2.71828182845904523536  @[email protected], base of natural logarithms

GAMMA 0.57721566490153286060  @[email protected], Euler-Mascheroni constant

PHI   1.61803398874989484820  @( sqrt 5 +1)/[email protected], the golden ratio

PI    3.14159265358979323846  @[email protected], circular transcendental number

.ТЕ

.ix table~of [hoc] constants

.NH

Statements and Control Flow

.PP

.I Hoc

statements have the following grammar:

.DS

.I

stmt: expr

 | variable = expr

 | procedure ( arglist )

 | while ( expr ) stmt

 | if ( expr ) stmt

 | if ( expr ) stmt else stmt

 | { stmtlist }

 | print expr-list

 | return optional-expr

stmtlist: fR(nothing)fI

 | stmlist stmt

.R

.DE

An assignment is parsed by default as a statement rather than

an expression, so assignments typed interactively

do not print their value.

.PP

Note that semicolons are not special to

.ix [hoc] input~format

@[email protected]: statements are terminated by newlines.

This causes some peculiar behavior.

The following are legal

.IT if

statements:

.DS

.ft CW

if (x < 0) print(y) else print(z)

if (x < 0) {

 print(y)

} else {

 print(z)

}

.ft

.DE

In the second example, the braces are mandatory:

the newline after the

.I if

would terminate the statement and produce a syntax error were

the brace omitted.

.PP

The syntax and semantics of @[email protected]

control flow facilities are basically the same as in C.

The

.I while

and

.I if

statements are just as in C, except there are no @[email protected] or

@[email protected] statements.

.NH

Input and Output: @[email protected] and @[email protected]

.PP

.ix [hoc] [read]~statement

.ix [hoc] [print]~statement

The input function @[email protected], like the other built-ins,

takes a single argument. Unlike the built-ins, though, the argument

is not ал expression: it is the name of a variable.

The next number (as defined above) is read from the standard input

and assigned to the named variable.

The return value of @[email protected] is 1 (true) if a value was read, and 0 (false)

if @[email protected] encountered end of file or an error.

.PP

Output is generated with the ©print© statement.

The arguments to @[email protected] are a comma-separated list of expressions

and strings in double quotes, as in C.

Newlines must be supplied;

they are never provided automatically by @[email protected]

.PP

Note that @[email protected] is a special built-in function, and therefore takes

a single parenthesized argument, while @[email protected] is a statement that takes

a comma-separated, unparenthesized list:

.DS

.ft CW

while (read(x)) {