Chapter 19: Advanced Text
19.8. Replacements

Suppose V is an indexed text which varies - perhaps a property of something, or a variable defined everywhere, or a temporary "let"-named value. How do we change its contents? The easiest way is simply to assign text to it. Thus:

let V be "It is now [the time of the day in words]."

And, for instance,

let V be "[V]!"

adds an exclamation mark at the end of V.

Otherwise, it is more useful (also a little faster) to modify V by changing its characters, words and so on. Thus:

replace character number N in V with NEW

changes the Nth character to NEW (which is not required to be a single character: it simply occupies the spot previously occupied by the Nth character). Similarly:

replace word number N in V with NEW
replace punctuated word number N in V with NEW
replace unpunctuated word number N in V with NEW
replace line number N in V with NEW
replace paragraph number N in V with NEW

Last, but not least, we can replace text wherever it occurs:

replace the text FIND in V with NEW
replace the text FIND in V with NEW, case insensitively
replace the regular expression FIND in V with NEW
replace the regular expression FIND in V with NEW, case insensitively

These match as much as they can, but again, with the matches not allowed to overlap. Thus

replace the text "a" in V with "z"

changes every lower-case "a" to "z": the same thing done case insensitively would change each "a" or "A" to "z".

When replacing a regular expression, the replacement text also has a few special meanings (though, thankfully, many fewer than for the expression itself). Once again "\n" and "\t" can be used for line break and tab characters, and "\\" must be used for an actual backslash. But, very usefully, "\1" to "\9" expand as the contents of groups numbered 1 to 9, and "\0" to the exact text matched. So:

replace the regular expression "\d+" in V with "roughly \0"

adds the word "roughly" in front of any run of digits in V, because \0 becomes in turn whichever run of digits matched. And

replace the regular expression "(\w+) (.*)" in V with "\2, \1"

performs the transformation "Frank Booth" to "Booth, Frank".

Finally, prefixing the number by "l" or "u" forces the text it represents into lower or upper case, respectively. For instance:

replace the regular expression "\b(\w)(\w*)" in X with "\u1\l2";

changes the casing of X to "title casing", where each individual word is capitalised. (This is a little slow on large texts, since so many matches and replacements are made: it's more efficient to use the official phrases for changing case.)


395
* Example  Blackout
Filtering the names of rooms printed while in darkness.

RB
396
* Example  Igpay Atinlay
A pig Latin filter for the player's commands.

RB
397
* Example  Fido
A dog the player can name and un-name at will.

RB

Suppose we'd like to have a dog which the player is allowed to name himself. We'd like to deal correctly with both

>name the dog fido

and

>name the dog "fido"

so we'll also need to strip quotation marks out of the command. We can do this as follows:

"Fido"

The Back Yard is a room.

A dog is an animal in Back Yard. The dog has some indexed text called the nickname. The nickname of the dog is "nothing". Understand the nickname property as describing the dog.

Rule for printing the name of the dog when the nickname of the dog is not "nothing":
    say "[nickname of the dog]"

Naming it with is an action applying to one thing and one topic. Understand "name [something] [text]" as naming it with. Check naming it with: say "You can't name that."

Instead of naming the dog with "nothing":
    change the nickname of the dog to "nothing";
    now the dog is improper-named;
    say "You revoke your choice of dog-name."

Instead of naming the dog with something:
    let N be indexed text; let N be "[the topic understood]";
    replace the text "'" in N with "";
    change the nickname of the dog to "[N]";
    now the dog is proper-named;
    say "The dog is now known as [nickname of the dog]."

Test me with "name the dog Fido / name the dog Lawrence / look / x lawrence / name Lawrence nothing / look / x lawrence".

398
** Example  Northstar
Making Inform understand ASK JOSH TO TAKE INVENTORY as JOSH, TAKE INVENTORY. This requires us to use a regular expression on the player's command, replacing some of the content.

RB
399
** Example  Mr. Burns' Repast
Letting the player guess types for an unidentifiable fish.

RB
400
*** Example  Cave-troll
Determining that the command the player typed is invalid, editing it, and re-examining it to see whether it now reads correctly.

RB


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