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1. Copy help.keyman.com/developer/17.0/* into /developer/docs/help 2. Update references to 18.0 where appropriate 3. Copy all referenced images from /cdn/dev into /developer/docs/help/images and update links in documentation Next commit: add deployment to help-keyman-com.sh. Note: simplest way to test links at this point is to use the help.keyman.com auto deploy and wait for the PR on help.keyman.com to be validated; we could look at an internal link validation tool that verifies markdown links? Relates-to: #12347
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title: Step 5: Rules with Context
Rules with Context
Very often we want a keyboard to produce different output based on more than just the last keystroke. For example, in the Quick French keyboard, we want the key e to produce one of è, é, ë, ê, or just e, depending on what was typed immediately before it. To do this we must make our rules look at the context.
The context is the output from previous rules; that is, the characters that are displayed on the screen. We can make a rule work with only certain context by putting this before the plus sign in the rule:
"^" + "e" > "ê"
With this rule, whenever an e is typed, if it was preceded by a caret (^), the output will be ê. It is important to remember that the context consists of output from previous rules, not the previous keystrokes. To emphasize this point, consider the four rules below:
+ "a" > "b"
+ "b" > "c"
"b" + "c" > "d"
"c" + "d" > "e"
With these rules, typing b c would produce the
output cc, and not d, as you might initially expect. This is because
the key b is converted by the second rule into
the output c, while the third rule expects a context of b, and not
c; we would have to type a c to get d.
However, if a key has no matching rule, the output will be the same as
the key: so the output e will be produced for either of the inputs c d (because c by itself has no rule), and b d.
Continuing the Quick French keyboard
Now we know how to create context-dependent rules, we can continue making the Quick French keyboard. Let's start with the rules for acute-accented characters, using the ANSI codes from the table we prepared earlier:
c lowercase characters with acute accent
"'" + "a" > U+00E1
"'" + "e" > U+00E9
"'" + "i" > U+00ED
"'" + "o" > U+00F3
"'" + "u" > U+00FA
"'" + "y" > U+00FD
c uppercase characters with acute accent
"'" + "A" > U+00C1
"'" + "E" > U+00C9
"'" + "I" > U+00CD
"'" + "O" > U+00D3
"'" + "U" > U+00DA
"'" + "Y" > U+00DD
We can also create similar rules for the other thirty-odd accented characters.
As you can see, even for a simple keyboard like this we quickly end up
with a large number of rules, which makes for clumsiness. We can make
things simpler using stores, and the any() and index() statements.