.. image:: /images/picF.png
:align: left
-.. raw:: latex
-
- \dropcap{f}
-
-inally our three example games are written; we've shown you as much of
-the Inform language as we've needed to, and made a lot of observations
-about how and why something should be done. Despite all that, there's
-much that we've left unsaid, or touched on only lightly. In this chapter
-we'll revisit key topics and review some of the more significant
-omissions, to give you a better feel for what's important, and what can
-be ignored for the time being; when you become an accomplished designer,
-you will decide what matters and what can be left on the shelf.
+|F|\inally our three example games are written; we've shown you as much of
+the Inform language as we've needed to, and made a lot of observations
+about how and why something should be done. Despite all that, there's much
+that we've left unsaid, or touched on only lightly. In this chapter we'll
+revisit key topics and review some of the more significant omissions, to
+give you a better feel for what's important, and what can be ignored for
+the time being; when you become an accomplished designer, you will decide
+what matters and what can be left on the shelf.
We'll also talk, in :ref:`reading-other-code`, about a few ways of doing
things that we've chosen not to tell you about, but which you're quite
Statements
==========
-.. todo::
-
- We might need some custom syntax highlighting here.
-
A :term:`statement` is an instruction intended for the interpreter, telling
it what to do at run-time. It *must* be given in lower-case, and always
ends with a semicolon.
Some statements, like ``if``, control one or more other statements. We
use the placeholder `{statement_block}` to represent either a single
-`{statement}`, or any number of `{statements}` enclosed in braces::
+`{statement}`, or any number of `{statements}` enclosed in braces:
- statement;
-
- { statement; statement; ... statement; }
+ | `{statement};`
+ |
+ | `{statement}; {statement}; ... {statement};`
Statements that we've met
-------------------------
Our games have used these statements, about half of the Inform
-possibilities::
-
- give obj_id attribute;
- give obj_id attribute attribute ... attribute;
-
- if (expression) statement_block
- if (expression) statement_block else statement_block
-
- move obj_id to parent_obj_id;
-
- objectloop (var_id) statement_block
-
- print value;
- print value, value, ... value;
-
- print_ret value;
- print_ret value, value, ... value;
-
- remove obj_id;
-
- return false;
- return true;
-
- style underline; print...; style roman;
-
- switch (expression) {
- value: statement; statement; ... statement;
- ...
- default: statement; statement; ... statement;
- }
-
- "string";
- "string", value, ... value;
-
- <action>;
- <action noun>;
- <action noun second>;
-
- <<action>>;
- <<action noun>>;
- <<action noun second>>;
+possibilities:
+
+ | `give {obj_id} {attribute};`
+ | `give {obj_id} {attribute} {attribute} ... {attribute};`
+ |
+ | `if ({expression}) {statement_block}`
+ | `if ({expression}) {statement_block} else {statement_block}`
+ |
+ | `move {obj_id} to {parent_obj_id};`
+ |
+ | `objectloop ({var_id}) {statement_block}`
+ |
+ | `print {value};`
+ | `print {value}, {value}, ... {value};`
+ |
+ | `print_ret {value};`
+ | `print_ret {value}, {value}, ... {value};`
+ |
+ | `remove {obj_id};`
+ |
+ | `return false;`
+ | `return true;`
+ |
+ | `style underline; print...; style roman;`
+ |
+ | `switch ({expression}) {`
+ | `{value}: {statement}; {statement}; ... {statement};`
+ | `...`
+ | `default: {statement}; {statement}; ... {statement};`
+ | `}`
+ |
+ | `"{string}";`
+ | `"{string}", {value}, ... {value};`
+ |
+ | `<{action}>;`
+ | `<{action} {noun}>;`
+ | `<{action} {noun} {second}>;`
+ |
+ | `<<{action}>>;`
+ | `<<{action} {noun}>>;`
+ | `<<{action} {noun} {second}>>;`
Statements that we've not met
-----------------------------
Although our example games haven't needed to use them, these looping
-statements are sometimes useful::
-
- break;
- continue;
+statements are sometimes useful:
- do statement_block until (expression)
-
- for (set_var : loop_while_expression : update_var) statement_block
-
- while (expression) statement_block
+ | `break;`
+ | `continue;`
+ |
+ | `do {statement_block} until ({expression})`
+ |
+ | `for ({set_var} : {loop_while_expression} : {update_var}) {statement_block}`
+ |
+ | `while ({expression}) {statement_block}`
On the other hand, we suggest that you put the following statements on
hold for now; they're not immediately relevant to everyday code and have
-mostly to do with printing and formatting::
+mostly to do with printing and formatting:
- box
- font
- jump
- new_line
- spaces
- string
+ | `box`
+ | `font`
+ | `jump`
+ | `new_line`
+ | `spaces`
+ | `string`
In particular, avoid using the deprecated jump statement if you possibly can.
Properties
----------
+.. Generated by autoindex
+.. index::
+ pair: before; library property
+ pair: name; library property
+
The library defines around forty-eight standard property variables (such
-as ``before`` or ``name``), but you can readily create further ones just
+as :prop:`before` or :prop:`name`), but you can readily create further ones just
by using them within an object definition.
You can create and initialise a property in an object's ``with`` segment:
obj_id.property() ! everywhere
+.. index::
+ single: arguments (of a routine)
+
Arguments and local variables
-----------------------------
[ routine_id; statement; statement; ... statement; ];
-returns ``true`` and ::
+.. Generated by autoindex
+.. index::
+ pair: true; library constant
+
+returns :const:`true` and ::
property [; statement; statement; ... statement; ]
-return ``false``.
+return :const:`false`.
This difference is *important*. Remember it by the letter pairs STEF:
left to themselves, Standalone routines return True, Embedded routines
if (MyVar) ...
Note that the following statement specifically tests whether ``MyVar``
- contains ``true`` (1), *not* whether its value is anything other than
+ contains :const:`true` (1), *not* whether its value is anything other than
zero. ::
if (MyVar == true) ...
"number" property and "general" attribute
-----------------------------------------
-The library defines a standard ``number`` property and a standard
-``general`` attribute, whose roles are undefined: they are
+.. Generated by autoindex
+.. index::
+ pair: general; library attribute
+ pair: number; library property
+
+The library defines a standard :prop:`number` property and a standard
+:attr:`general` attribute, whose roles are undefined: they are
general-purpose variables available within every object to designers as
and when they desire.
Setting up the object tree
--------------------------
+.. Generated by autoindex
+.. index::
+ pair: found_in; library property
+
Throughout this guide, we've defined the initial position of each object
within the overall object tree either by explicitly mentioning its
parent's ``obj_id`` (if any) in the first line of the object definition
-- what we've been calling the header information -- or, for a few
objects which crop up in more than one place, by using their
-``found_in`` properties. For example, in "William Tell" we defined
-twenty-seven objects; omitting those which used ``found_in`` to define
+:prop:`found_in` properties. For example, in "William Tell" we defined
+twenty-seven objects; omitting those which used :prop:`found_in` to define
their placement at the start of the game, we're left with object
definitions starting like this::
projects / ibg.git / blobdiff