66.7.2 CCL Statements

The SXEmacs Code Conversion Language provides the following statement types: set, if, branch, loop, repeat, break, read, write, call, and end.

Set statement:

The set statement has three variants with the syntaxes ‘(reg = expression)’, ‘(reg assignment_operator expression)’, and ‘integer’. The assignment operator variation of the set statement works the same way as the corresponding C expression statement does. The assignment operators are +=, -=, *=, /=, %=, &=, |=, ^=, <<=, and >>=, and they have the same meanings as in C. A "naked integer" integer is equivalent to a set statement of the form (r0 = integer).

I/O statements:

The read statement takes one or more registers as arguments. It reads one byte (a C char) from the input into each register in turn.

The write takes several forms. In the form ‘(write reg ...)’ it takes one or more registers as arguments and writes each in turn to the output. The integer in a register (interpreted as an Emchar) is encoded to multibyte form (ie, Bufbytes) and written to the current output buffer. If it is less than 256, it is written as is. The forms ‘(write expression)’ and ‘(write integer)’ are treated analogously. The form ‘(write string)’ writes the constant string to the output. A "naked string" ‘string’ is equivalent to the statement ‘(write string)’. The form ‘(write reg array)’ writes the regth element of the array to the output.

Conditional statements:

The if statement takes an expression, a CCL block, and an optional second CCL block as arguments. If the expression evaluates to non-zero, the first CCL block is executed. Otherwise, if there is a second CCL block, it is executed.

The read-if variant of the if statement takes an expression, a CCL block, and an optional second CCL block as arguments. The expression must have the form (reg operator operand) (where operand is a register or an integer). The read-if statement first reads from the input into the first register operand in the expression, then conditionally executes a CCL block just as the if statement does.

The branch statement takes an expression and one or more CCL blocks as arguments. The CCL blocks are treated as a zero-indexed array, and the branch statement uses the expression as the index of the CCL block to execute. Null CCL blocks may be used as no-ops, continuing execution with the statement following the branch statement in the containing CCL block. Out-of-range values for the expression are also treated as no-ops.

The read-branch variant of the branch statement takes an register, a CCL block, and an optional second CCL block as arguments. The read-branch statement first reads from the input into the register, then conditionally executes a CCL block just as the branch statement does.

Loop control statements:

The loop statement creates a block with an implied jump from the end of the block back to its head. The loop is exited on a break statement, and continued without executing the tail by a repeat statement.

The break statement, written ‘(break)’, terminates the current loop and continues with the next statement in the current block.

The repeat statement has three variants, repeat, write-repeat, and write-read-repeat. Each continues the current loop from its head, possibly after performing I/O. repeat takes no arguments and does no I/O before jumping. write-repeat takes a single argument (a register, an integer, or a string), writes it to the output, then jumps. write-read-repeat takes one or two arguments. The first must be a register. The second may be an integer or an array; if absent, it is implicitly set to the first (register) argument. write-read-repeat writes its second argument to the output, then reads from the input into the register, and finally jumps. See the write and read statements for the semantics of the I/O operations for each type of argument.

Other control statements:

The call statement, written ‘(call ccl-program-name)’, executes a CCL program as a subroutine. It does not return a value to the caller, but can modify the register status.

The end statement, written ‘(end)’, terminates the CCL program successfully, and returns to caller (which may be a CCL program). It does not alter the status of the registers.