User guide

Appendix A

BCPL Syntax Diagrams

The syntax of standard B CPL is speciﬁed using the transition diagrams given in ﬁg-

ures A.1, A.2, A.3 and A.4. In extended BCPL the ﬂoating point operators have

the same precedence as the corresponding integer ones, and the op:= operators are

syntactically identical to the := operator. The syntax of the more binding sequenc-

ing operator (<>) requi r e s some new diagr ams to be drawn. This wi l l be done i n

due c our se . It is suﬃcient to know that <> is more binding than DO, THEN, ELSE,

REPEAT, REPEATWHILE, REPEATUNTIL, and colon. Within the diagrams the syntactic

categories program, secti o n , declaration, command and expression

are represented

by the rounded boxes:

program

section

and

, respec-

tively.

The rectangular boxes are called test boxes and can only be traversed if the c on-

dition labelling the box matches the current input. When the label is a token, as in

WHILE

and

, it must match the next input token for the test t o succeed. The

test box

eof

is only satisﬁed if the end of ﬁle has been reached. Sometimes the

test box contains a side condition, as in

REM n<6

, in which case the side condition

must also be satisﬁed. The only other test boxes are

is call

and

is name

which

are only satisﬁed i f the most recently read expressi on is syntactically a function call

or a name, respectively. By setting n successively from 0 to 8 in the deﬁnition of the