Liblouis User's and Programmer's Manual

2.11 Swap Opcodes ¶

The swap opcodes are needed to tell the context opcode (see context), the correct opcode (see correct) and multipass opcodes which dot patterns to swap for which characters. There are three, swapcd, swapdd and swapcc. The first swaps dot patterns for characters. The second swaps dot patterns for dot patterns and the third swaps characters for characters. The first is used in the context opcode and the second is used in the multipass opcodes.

All the swap opcodes have a name so they can be referred to from the context, correct and multipass opcodes. The name operand must contain only letters (a-z and A-Z). The letters may be upper or lower-case but the case matters.

Dot patterns are separated by commas and may contain more than one cell.

swapcd name characters dots, dots, dots, ...

See above paragraph for explanation. For example:

swapcd dropped 0123456789 356,2,23,...

swapdd name dots, dots, dots ... dotpattern1, dotpattern2, dotpattern3, ...

The swapdd opcode defines substitutions for the multipass opcodes. In the second operand the dot patterns must be single cells, but in the third operand multi-cell dot patterns are allowed. This is because multi-cell patterns in the second operand would lead to ambiguities.

swapcc name characters characters

The swapcc opcode swaps characters in its second operand for characters in the corresponding places in its third operand. It is intended for use with correct opcodes and can solve problems such as formatting phone numbers.