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move meta to special forms from core functions

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This commit is contained in:
Pekka Laiho 2020-12-08 08:25:53 +07:00
parent 1151ebe336
commit 87cff43e93
3 changed files with 44 additions and 31 deletions
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7
README.md
View File

@ -214,17 +214,20 @@ The `quasiquote` form described above is essential for declaring macros. Interna
## Reflection
You can use the `meta` function to retrieve the arguments, body or full code of user-defined functions:
You can use the `meta` special form to retrieve the arguments, body, code or full definition of user-defined functions:
```text
> (defn add (a b) (+ a b))
<function>
> (meta add "args")
(a b)
> (meta add "body")
(+ a b)
> (meta add "code")
(fn (a b) (+ a b))
> (meta add "def")
(defn add (a b) (+ a b))
```
This allows for some fun tricks. For example, we can retrieve the body of a function and evaluate it as part of another function:
@ -257,6 +260,7 @@ let | yes | `(let (a (+ 1 2)) a)` | `3` | Create a new local environment using
load | no | `(load "file.mad")` | | Read and evaluate a file. The contents are implicitly wrapped in a `do` expression.
macro | yes | | | See the section Macros.
macroexpand | yes | | | See the section Macros.
meta | no | | | See the sections Environments and Reflection.
or | yes | `(or false 0 1)` | `1` | Return the first value that evaluates to true, or the last value.
quote | yes | | | See the section Quoting.
quasiquote | yes | | | See the section Quoting.
@ -274,7 +278,6 @@ doc | yes | `(doc +)` | `"Return the sum of all arguments."` | Show the docume
error | yes | `(error "invalid value")` | `error: invalid value` | Throw an exception with message as argument.
exit | no | `(exit 1)` | | Terminate the script with given exit code using [exit](https://www.php.net/manual/en/function.exit.php).
loop | yes | `(loop (fn (a) (do (print a) (coinflip))) "hello ")` | `hello hello hello false` | Call the given function repeatedly in a loop until it returns false.
meta | no | `(meta (env) "name")` | `"root/user"` | Read meta information of an entity.
print | no | `(print "hello world")` | `"hello world"null` | Print expression on the screen. Print returns null (which is shown due to the extra print in repl). Give optional second argument as `true` to show strings in readable format.
read | no | `(read "(+ 1 2 3)")` | `(+ 1 2 3)` | Read a string as code and return the expression.
sleep | no | `(sleep 2000)` | `null` | Sleep for the given period given in milliseconds using [usleep](https://www.php.net/manual/en/function.usleep).

39
src/Evaller.php
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@ -295,6 +295,45 @@ class Evaller
}
return $this->macroexpand($astData[1], $env);
} elseif (!$this->safemode && $symbolName == 'meta') {
if ($astLength != 3) {
throw new MadLispException("meta requires exactly 2 arguments");
} elseif (!is_string($astData[2])) {
throw new MadLispException("third argument to meta is not string");
}
$obj = $this->eval($astData[1], $env, $depth + 1);
$attribute = $astData[2];
if ($obj instanceof Env) {
if ($attribute == 'name') {
return $obj->getFullName();
} elseif ($attribute == 'parent') {
return $obj->getParent();
} else {
throw new MadLispException('unknown attribute for meta');
}
} elseif ($obj instanceof UserFunc) {
if ($attribute == 'args') {
return $obj->getBindings();
} elseif ($attribute == 'body') {
return $obj->getAst();
} elseif ($attribute == 'code') {
$name = $obj->isMacro() ? 'macro' : 'fn';
return new MList([new Symbol($name), $obj->getBindings(), $obj->getAst()]);
} elseif ($attribute == 'def') {
if ($astData[1] instanceof Symbol) {
$def = $obj->isMacro() ? 'defmacro' : 'defn';
return new MList([new Symbol($def), $astData[1], $obj->getBindings(), $obj->getAst()]);
} else {
throw new MadLispException('no name for def in meta');
}
} else {
throw new MadLispException('unknown attribute for meta');
}
} else {
throw new MadLispException('unknown entity for meta');
}
} elseif ($symbolName == 'or') {
if ($astLength == 1) {
return false;

29
src/Lib/Core.php
View File

@ -85,35 +85,6 @@ class Core implements ILib
}
));
if (!$this->safemode) {
$env->set('meta', new CoreFunc('meta', 'Read meta information of an entity.', 2, 2,
function ($obj, $attribute) {
if ($obj instanceof Env) {
if ($attribute == 'name') {
return $obj->getFullName();
} elseif ($attribute == 'parent') {
return $obj->getParent();
} else {
throw new MadLispException('unknown attribute for meta');
}
} elseif ($obj instanceof UserFunc) {
if ($attribute == 'args') {
return $obj->getBindings();
} elseif ($attribute == 'body') {
return $obj->getAst();
} elseif ($attribute == 'code') {
$name = $obj->isMacro() ? 'macro' : 'fn';
return new MList([new Symbol($name), $obj->getBindings(), $obj->getAst()]);
} else {
throw new MadLispException('unknown attribute for meta');
}
} else {
throw new MadLispException('unknown entity for meta');
}
}
));
}
if (!$this->safemode) {
$env->set('print', new CoreFunc('print', 'Print argument. Give second argument as true to show strings in readable format.', 1, 2,
function ($a, bool $readable = false) {