HOC Keywords¶ ↑
help
invokes the help system
- Syntax:
help
help word
- Description:
Help word
sends a word to the help system. The word is looked up in thenrn/lib/helpdict
file and if found Netscape is sent the appropriate URL to display the help text. If the word is not found, the URL for the table of contents is sent. Netscape must be running for the help system to work.
return
- Syntax:
return
return expr
return objref
- Description:
The
return
command will immediately exit from a procedure without returning a value.The
return expr
command will immediately exit from a function which must return a value. This command must also be the last executable statement of a function. It is possible for a function to contain more than onereturn
command, for instance in a series ofif else
statements; however, not more than one of thereturn
commands may return a value at any given time.The
return objref
command must be used to return from an obfunc.Example:
func max(){ if ($1 > $2){ return $1 } else { return $2 } }returns the maximum of two arguments which are read into the function. Eg.
max(3,6)
, where $1 is the first argument (3) and $2 is the second argument (6). This use ofmax
would return the value 6.Warning
See restriction of the break statement.
break
- Syntax:
break
- Description:
- Immediately exit from a loop. Control transfers to the next statement after the loop statement.
Warning
This statement, as well as “return”, “continue”, and “stop” cannot occur within the scope of a statement that modifies the section stack such as
section { statement }
or the stack will not be properly popped. Also it should not be placed on a line that contains object syntax but should be placed on a line by itself. eg.
x.p() breakshould be written
x.p() breakExample:
while(1) { x = fscan() if (x < 0) { break; } print sqrt(x) }
continue
- Syntax:
continue
- Description:
- Inside a compound statement of a loop, transfers control to the next iteration of the loop statement.
Example:
for i=1,10{ if(i==6){ continue } print i }prints the numbers: 1,2,3,4,5,7,8,9,10. 6 is left out because when i==6, the control is passed beyond the print statement to the next iteration of the loop.
You can accomplish the same thing with the following syntax:
for i=1,10{ if(i<6 || i>6){ print i } }Warning
See restriction of the break statement.
stop
- Syntax:
stop
- Description:
- Return control to the command level of the interpreter. This is a useful safety device for stopping the current execution of your program. Eg. you may wish to stop the program and print out an error message that lets you know if you have entered unacceptable arguments.
Warning
See restriction of the break statement.
if
- Syntax:
if (expr) stmt1
if (expr) stmt1 else stmt2
- Description:
- Conditional statement. When the expr evaluates to a nonzero number (true) stmt1 is executed. With the
else
form, if the expression evaluates to zero (false) stm2 is executed.Example:
i = 0 //initialize i j = 0 //initialize j if(vec.x[i] <= 10 && i < vec.size()){ //if the value of the ith element in vec //is less than or equal to 10, and //if i is an index within vec vec1.x[j] = vec.x[i] //set the jth element of vec1 equal to that //ith element of vec i = i+1 //increment i by 1 j = j+1 //increment j by 1 } else{ //otherwise (This must be on the same line as the closing brace of //the previous statement in order to indicate that the compound //statement has not ended.) i = i+1 //simply go to the next element of vec }See also
else
See also
while
- Syntax:
while (expr) stmt
- Description:
- Iteration statement. Repeatedly execute the statement as long as the expr evaluates to true.
Example:
numelements = 20 i = 0 while (i < numelements){ print(cos(vec.x[i])) print(sin(vec.x[i])) i += 1 }prints the cosines and the sines of the
vec
elements up tonumelements
, which in this case = 20.
for
- Syntax:
for(stmt1; expr2; stmt3) stmt
for var=expr1, expr2 stmt
for (var) stmt
for (var, expr) stmt
for iterator (args) stmt
- Description:
Iteration statement. The
for
statement is similar towhile
in that it iterates over a statement. However, thefor
statement is more compact and contains within its parentheses the command to advance to the next iteration. Statements 1 and 3 may be empty.This command also has a short form which always increments the iterations by one.
for *var*=*expr1*, *expr2* stmtis equivalent to
for(*var*=*expr1*; *var* <= *expr2*; *var*=*var*+1) stmtHowever, expr1 and expr2 are evaluated only once at the beginning of the
for
.
for (var) stmt
Loops over all segments of the currently accessed section. var begins at 0 and ends at 1. In between var is set to the center position of each segment. Ie. stmt is executed nseg+2 times.
for (var, expr) stmt
If the expression evaluates to a non-zero value, it is exactly equivalent to
for (var) stmt
If it evaluates to 0 (withinfloat_epsilon
) then the iteration does not include the 0 or 1 points. Thusfor(x, 0) { print x }
is exactly equivalent tofor (x) if (x > 0 && x < 1) { print x }
The iterator form of the for loop executes the statement with a looping construct defined by the user.
Example:
for(i=0; i<=9; i=i+1){ print i*2 }is equivalent to
for i=0, 9 { print i*2 }create axon access axon {nseg = 5 L=1000 diam=50 insert hh } for (x) print x, L*x for (x) if (x > 0 && x < 1) { print x, gnabar_hh(x) }
- Syntax:
print expr, string, ...
- Description:
- Any number of expressions and/or strings may be printed. A newline is printed at the end.
Example:
x=2 y=3 print x, "hello", "good-bye", y, 7prints
x hello good-bye 3 7and then moves to the next line.
delete
- Syntax:
delete varname
- Description:
- Deletes the variable name from the global namespace. Allows the varname to be declared as another type. It is up to the user to make sure it is safe to execute this statement since the variable may be used in an existing function.
read
- Syntax:
read(var)
- Description:
- var is assigned the number input by the user, or the next number in the standard input, or the file opened with ropen.
read(var)
returns 0 on end of file and 1 otherwise.Example:
for i=1, 5 { read(x) print x*x }will await input from the user or from a file, and will print the square of each value typed in by the user, or read from the file, for the first five values.
See also
debug
A toggle for parser debugging purposes. Prints the stack machine commands resulting from parsing a statement. Not useful to the user.
double
- Syntax:
double var1[expr]
double var2[expr1][expr2]
double varn[expr1][expr2]...[exprn]
- Description:
Declares a one-dimensional, a two-dimensional or an n-dimensional array of doubles. This is reminiscent of the command which creates an array in C, however, HOC does not demand that you specify whether or not numbers are integers. All numbers in all arrays will be doubles.
The index for each dimension ranges from 0 to expr-1. Arrays may be redeclared at any time, including within procedures. Thus arrays may have different lengths in different objects.
The
Vector
class for the ivoc interpreter provides convenient and powerful methods for manipulating arrays.Example:
double vec[40]declares an array with 40 elements, whereas
objref vec vec = new Vector(40)creates a vector (which is an array by a different name) with 40 elements which you can manipulate using the commands of the Vector class.
em
- Syntax:
em
- Description:
microemacs editor
This is a reasonably complete editor with many commands. These commands are listed in emacs. A tutorial is also available at emacstut.
When called from the interpreter, the command
^C
immediately returns to the interpreter and the current buffer is interpreted. Other commands follow:
^X^F
- reads a file into a new buffer.
^X^B
- changes buffers.
^X^W
filename- saves (writes) a file under a specific name.
^X^S
- saves a file under the last specified name.
depvar
- Syntax:
depvar
- Description:
- Declare a variable to be a dependent variable for the purpose of solving simultaneous equations.
Example:
depvar x, y, z proc equations() { eqn x:: x + 2*y + z = 6 eqn y:: x - y + z = 2 eqn z:: 2*x + y -z = -3 } equations() solve() print x,y,zprints the values of x, y and z.
eqn
- Syntax:
eqn var:: expr = expr
eqn var: expr =
eqn var: = expr
- Description:
- Introduce a simultaneous equation. The single colon forms add the expressions to the indicated sides. This is convenient for breaking long equations down into more manageable parts which can be added together.
Example:
eqinit() depvar x, y, z proc equations() { eqn x:: x + 2*y + z = 6 eqn y:: x - y + z = 2 eqn z:: 2*x + y -z = -3 eqn z: = 5 + 4y } equations() solve() print x,y,zmakes the right hand side of the z equation “2 + 4y” and solves for the values x, y, and z.
local
- Syntax:
local var
- Description:
- Declare a list of local variables within a procedure or function Must be the first statement on the same line as the function declaration.
Example:
func count() {local i, x x = 0 for i=0,40 { if (vec.x[i] == 7) { x = x+1 } } return x }returns the number of elements which have the value of 7 in the first 40 elements of
vec
.i
andx
are local variables, and their usage here will not affect variables of the same name in other functions and procedures of the same program.
localobj
- Syntax:
localobj var
- Description:
- Declare a list, comma separated, of local objrefs within a proc, func, iterator, or obfunc. Must be after the local statement (if that exists) on the same line as the function declaration
Example:
func sum() { local i, j localobj tobj // sum from $1 to $2 i = $1 j = $2 tobj = new Vector() tobj.indgen(i, j ,1) return tobj.sum } sum(5, 10) == 45
strdef
- Syntax:
strdef stringname
- Description:
Declare a comma separated list of string variables. String variables cannot be arrays.
Strings can be passed as arguments to functions.
Example:
strdef a, b, c a = "Hello, " b = "how are you?" c = "What is your name?" print a, b print cwill print to the screen:
Hello, how are you? What is your name?
setpointer
- Syntax:
setpointer pvar, var
- Description:
Connects pointer variables in membrane mechanisms to the address of var. eg. If
$NEURONHOME/examples/nmodl/synpre.mod
is linked into NEURON, then:soma1 syn1=new synp(.5) setpointer syn1.vpre, axon2.v(1)would enable the synapse in soma1 to observe the axon2 membrane potential.
insert
- Syntax:
insert mechanism
- Description:
- Insert the density mechanism in the currently accessed section. Not used for point processes–they are inserted with a different syntax.
See also
hh, pas, fastpas,
psection()
, Point Processes and Artificial Cells
uninsert
- Syntax:
uninsert mechanism
- Description:
- Delete the indicated mechanism from the currently accessed section. Not for point processes.