file: job.t package: muf status: alpha
This construct is a multiway branch corresponding to the
Pascal case and C switch statements, except
that the constants may be any values, including strings.
(I've frequently wished that C allowed string keys in
switch!) The MUF version also has the advantage
of being able to return a value, unlike either the C or
Pascal versions. (Ansi Forth has a multiway branch also,
but its semantics seem twisted enough to cause continual
problems for novice programmers; After some thought, I
decided to break new ground.)
Stack:
: xlt { $ -> $ } case{ on: 1 "one" on: 2 "two" else: "many" } ;
Stack:
1 xlt
Stack: "one"
pop 2 xlt
Stack: "two"
pop 3 xlt
Stack: "many"
The case{ operator pops one value off the stack
and compares it with all provided on: constants until
it finds a match. If it finds a match, it executes the
associated code clause; otherwise, it executes the
else: code clause, if present.
The current MUF compilers produce code which simply
scans all on: clauses in order until a match is
found: It may be wise to put the most frequently used cases
first if speed is an issue.
Note that, unlike C, the MUF case{ statement
does not require that clauses be separated by break
operators. This feature of C tends to cause obscure bugs,
to puzzle newcomers (particularly those trained on Pascal),
and to add unneeded verbosity: Try translating the above
one-liner into C.
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