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update quoting

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Pekka Laiho 2020-12-05 17:54:46 +07:00
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@ -117,13 +117,40 @@ Symbols are words which do not match any other type and are separated by whitesp
## Quoting ## Quoting
The special single quote character can be used to quote an expression (skip evaluation). Use the `quote` special form to skip evaluation:
``` ```
> (quote (1 2 3))
(1 2 3)
> '(1 2 3) > '(1 2 3)
(1 2 3) (1 2 3)
``` ```
Use the `quasiquote` special form when you need to turn evaluation back on inside the quoted element. The special forms `unquote` and `unquote-splice` are available for that purpose:
```
> (def lst (quote (2 3)))
(2 3)
> (quasiquote (1 lst 4))
(1 lst 4)
> (quasiquote (1 (unquote lst) 4))
(1 (2 3) 4)
> (quasiquote (1 (unquote-splice lst) 4))
(1 2 3 4)
```
### Shortcuts
You can use the single-quote (`'`), backtick and tilde (`~`) characters as shortcuts for `quote`, `quasiquote` and `unquote` respectively:
```
> (def lst '(2 3))
(2 3)
> `(1 ~lst 4)
(1 (2 3) 4)
```
## Environments ## Environments
Environments are hash-maps which store key-value pairs and use symbols as keys. Symbols are evaluated by looking up the corresponding value from the current environment. If the key is not defined in current environment the lookup proceeds to the parent environment and so forth. The initial environment is called `root` and contains all the built-in functions listed here. Then another environment called `user` is created for anything the user wants to define. The `let` and `fn` special forms create new local environments. Note that `def` always uses the current environment, so anything defined with `def` is not visible in the parent environment. Environments are hash-maps which store key-value pairs and use symbols as keys. Symbols are evaluated by looking up the corresponding value from the current environment. If the key is not defined in current environment the lookup proceeds to the parent environment and so forth. The initial environment is called `root` and contains all the built-in functions listed here. Then another environment called `user` is created for anything the user wants to define. The `let` and `fn` special forms create new local environments. Note that `def` always uses the current environment, so anything defined with `def` is not visible in the parent environment.
@ -158,7 +185,8 @@ if | yes | `(if (< 1 2) "yes" "no")` | `"yes"` | If the first argument evalua
let | yes | `(let (a (+ 1 2)) a)` | `3` | Create a new local environment using the first argument (list) to define values. Odd arguments are treated as keys and even arguments are treated as values. The last argument is the body of the let-expression which is evaluated using this new environment. let | yes | `(let (a (+ 1 2)) a)` | `3` | Create a new local environment using the first argument (list) to define values. Odd arguments are treated as keys and even arguments are treated as values. The last argument is the body of the let-expression which is evaluated using this new environment.
load | no | `(load "file.mad")` | | Read and evaluate a file. The contents are implicitly wrapped in a `do` expression. load | no | `(load "file.mad")` | | Read and evaluate a file. The contents are implicitly wrapped in a `do` expression.
or | yes | `(or false 0 1)` | `1` | Return the first value that evaluates to true, or the last value. or | yes | `(or false 0 1)` | `1` | Return the first value that evaluates to true, or the last value.
quote | yes | `(quote (1 2 3))` | `(1 2 3)` | Return the argument without evaluation. This is same as the `'` shortcut described above. quote | yes | | | See the section Quoting.
quasiquote | yes | | | See the section Quoting.
## Functions ## Functions