lfCW n l.
\fBTable 3:\fP Built-in Constants
.sp .5
DEG 57.29577951308232087680 @180/ pi@, degrees per radian
E 2.71828182845904523536 @e@, base of natural logarithms
GAMMA 0.57721566490153286060 @gamma@, Euler-Mascheroni constant
PHI 1.61803398874989484820 @( sqrt 5 +1)/2@, the golden ratio
PI 3.14159265358979323846 @pi@, 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
@hoc@: 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 @hoc@
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 @break@ or
@continue@ statements.
.NH
Input and Output: @read@ and @print@
.PP
.ix [hoc] [read]~statement
.ix [hoc] [print]~statement
The input function @read@, 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 @read@ is 1 (true) if a value was read, and 0 (false)
if @read@ encountered end of file or an error.
.PP
Output is generated with the ©print© statement.
The arguments to @print@ 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 @print@.
.PP
Note that @read@ is a special built-in function, and therefore takes
a single parenthesized argument, while @print@ is a statement that takes
a comma-separated, unparenthesized list:
.DS
.ft CW
while (read(x)) {
print "value is ", x, "\n"
}
.ft
.DE
.NH
Functions and Procedures
.PP
Functions and procedures are distinct in @hoc@,
although they are defined by the same mechanism.
This distinction is simply for run-time error checking:
it is an error for a procedure to return a value,
and for a function @not@ to return one.
.PP
The definition syntax is:
.ix [hoc] function~definition
.ix [hoc] procedure~definition
.DS
