Got to 3 Numbers..
C-x C-e reads and evaluates some emacs lisp.
It's somehow important that read and evaluate are separate stages.
Comments are ;
nil means (), FALSE or nil
eq for reference equals,
equal for testing equality of values, and
equal-including-properties, which also accounts for text properties.
Variables and Standard Types
'thing is a variable
Variables are (mostly) untyped, but values are typed. This is dynamic type.
There are type predicates for checking types, like
listp and so on.
- Integer (signed, width depends on machine)
- floating-point (signed double)
- character - prepend with ? in source code, e.g. '?Q'.
- may need escaping with '\'
- ?\UNNNN for a unicode character
- ?\C-g or ?\g represents ctrl + g
- ?\M-g represents alt + g (actually meta, but whatever)
- ?§-g represents shift + g
- You can combine the modifiers ?\C-M-S-g
- string is an array of characters
- it can hold ASCII control characters, but not other control characters (C-char)
- symbol is a type of interned string used to name things
- distinct upper and lower case
- keyword is a symbol starting with :
- empty string symbol prints as ##
- linked lists made of cons cells
- empty list () is always equal to nil
- an atom is anything other than a cons cell
- car means first and cdr means rest (really pointer to rest)
- you can represent cons as
(a . b), which can be useful if b is not itself list
- association lists or alist is a list of lists with keys and values
- ((key1 value1) (key2 value2))
- arrays (fixed-length, one-dimensional)
- char tables are indexed by character
- A vector can contain mixed types
- a bool vector contains true or nil
- hash tables are faster than alists
Arrays and lists both fit into the sequence abstraction.
Elisp doesn't expose pointers.
frexpbreaks down a floating point number into significand and exponent. X = S * 2**E.
wholenumpis the natural number predicate
- use = to compare numbers, since sometimes floating point and integer should be equal
Write NaN as 0.0e+NaN and infinity as 1.0e+INF or -1.0e+INF.
There aren't any builtin bigints.
There are separate rounding functions for returning an integer or a floating point number.
A function is a list.
If it isn't compiled, the first item in the list is the symbol lambda
You can call functions with funcall and apply.
These are C functions.
Don't redefine them, it'll end badly.
(symbol-function 'builtin-function) to get a handle to them.
(subrp (symbol-functuin 'builtin-function)) to test if a function is primitive.
Compiling a function makes a byte-code function.
They look like #[some stuff] in the output.
A list which starts with autoload will go and get the function from a file on demand.
Use autoload to make these.
Don't evaluate their arguments.
They are a list with the symbol macro at the front.
They return a function.
Make them with defmacro.
These are special types for Emacs, which aren't in normal LISPs.
Buffers are string-like with nice editing properties and some extra bits:
- syntax table
- local variables
- overlays apply a property list to a range of the buffer
- text properties
Indirect buffers are a view onto some other buffer.
Windows, one of which is the selected window. Windows are grouped into frames, which are grouped into terminals.
A frame also has a window configuration to describe the layout of windows inside it.
There is one frame configuration, which is a list beginning with the word frame-configuration. It describes all the window configurations for everything.
Processes are objects which describe actual subprocesses made by Emacs.
Streams are a source or sink of characters. Nil used as a stream means either standard-input or standard-output. t used as a stream means the minibuffer.
Fonts. There are also font specs and font entities.
Reading Types with Cycles
#1= assigns the thing after = to be 1.
#1# uses 12
This is also useful is you want to reuse exactly the same object in two places, instead of two different-but-equal objects.
You can write text properties inside strings to tag them with display information.
This can happen automatically.
Has lexical scope per-file.
lexical-binding variable controls this.