User guide

60 CHAPTER 3. THE LIBRARY

res := release(taskid) CIN:n, POS:y, NAT:n

This Cintpos function wi l l clear the HOLD bit in the spe ci ﬁ ed task thus making it

potential l y runnable. It returns a non zero value if successful. If the speciﬁed task does

not exist it returns zero with 101 in result2. If the released task has highe r priority

and is runnable it gaids control leaving the current task suspended in RUN state.

ﬂag := renamefile(oldname, newname) CIN:y, POS:y, NAT:y

The call renames the ﬁle oldname as ﬁle newname, deleting newname if necessary,

returning TRUE if the renaming was successful, and FALSE otherwise. Both oldname

and newname are strings.

res := resumeco(cptr, arg) CIN:y, POS:y, NAT:y

The eﬀec t of resumeco is almost identical t o that of callco, diﬀe r i ng only in the

treatment of the parent. With resumeco the parent of the calling coroutine becomes

the parent of the called coroutine, leaving the calling coroutine suspended and without

a parent. Systematic use of resumeco reduces the number of coroutines having parents

and henc e allows greater freedom in organising the ﬂow of control betwe en coroutines.

The deﬁnition of resumeco is in blib.b and is as follows.

LET resumeco(cptr, a) = VALOF

{ LET parent = currco!co_parent

currco!co_parent := 0

IF cptr!co_parent DO abort(111)

cptr!co_parent := parent

RESULTIS changeco(a, cptr)

}

res := rewindstream(scb) CIN:y, POS:y, NAT:y

This function set the position of stream scb to its start, returning TRUE i f successful,

and FALSE oth er wi se .

ch := sardch() CIN:y, POS:y, NAT:y

This function calls sys(Sys

sardch) to read the next character from the keyboard

as soon as it is available, echoing the character to the screen.

sawrch(ch) CIN:y, POS:y, NAT:y

This function calls sys(Sys

sawrch(ch) to write the speciﬁed character to the

screen.

sawritef(format,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z)

CIN:y, POS:y, NAT:y

This function is similar to writef but performs its output using sawrch.

selectinput(scb) CIN:y, POS:y, NAT:y

This call executes cis := scb to select scb as the current input stream. It aborts

(with code 186) if scb is not an input stream.