PlsExplain: A small dynamic programming language the keep every price is explained
A small dynamically typed programming language with first-class feedback, the keep every price is explained by a commentary.
Working the Interpreter
Dependencies
The interpreter is reckoning on python3 and lark. Lark might maybe furthermore be installed with pip set up lark.
REPL
Invoke the interpreter with out inform line arguments to initiate the interactive mode
To exit press Ctrl-D.
Working a Scripts
To attain a script written in PlsExplain, pass it as the critical inform line argument.
$ ./pls_explain.py examples/hello_world.pe
Hi there World /*the string "Hi there World"*/
First-Class Comments
Comments are first-class values in PlsExplain. Which capacity they’re expressions, might maybe furthermore be saved in variables, passed as feature arguments and be returned by suggestions.
>>> print(x)
42 /the number fourtytwo */
“>
>>> let x = 40 + 2 /the number fourtytwo */;
>>> print(x)
42 /the number fourtytwo */
Explaining feedback fabricate no longer must be commentary-literals:
Backtrace (most up-to-date call final):
line 1:
42 “this is no longer a commentary”
^~~~~~~~~~~~~~~~~~~~~~~~~~
form error: form JlString can no longer be stale to conceal values
>>> let s = “no longer a commentary either”
“>
>>> 42 "this is no longer a commentary"
Backtrace (most up-to-date call final):
line 1:
42 "this is no longer a commentary"
^~~~~~~~~~~~~~~~~~~~~~~~~~
form error: form JlString can no longer be stale to conceal values
>>> let s = "no longer a commentary either"
Whilst you to find this error, it in most cases capacity that you occupy forgotten to separate two expressions with an semicolon.
Auto-generated Comments
If a price is no longer explained by an train commentary, the interpreter automagically generates a beneficial commentary.
The commentary explaining a price might maybe furthermore be retrieved with the ?operator.
The auto-generated commentary can infrequently be a little bit bit verbose:
let truth = fn(n) {
if (n == 0) {
1
} else {
truth(n - 1) n;
}
};
print(truth(4));
This program prints:
24.0 /*the fabricated from the fabricated from the fabricated from the product
of the number 1.0 and the adaptation of the adaptation of
the adaptation of the number 4.0 and the number 1.0 and the
number 1.0 and the number 1.0 and the adaptation of the
distinction of the number 4.0 and the number 1.0 and the number
1.0 and the adaptation of the number 4.0 and the number 1.0
and the number 4.0*/
Since feedback are first-class values we can manipulate them on the hobble. This permits us to generate some distance more beneficial feedback.
let truth = fn(n) {
if (n == 0) {
1
} else {
/lets generate a beneficial commentary for the return price */;
/(Comments might maybe furthermore be concatenated with +) */
let commentary = /the factorial of */ + n?;
/conceal the return price with the generated commentary */
(truth(n - 1) n) commentary;
}
};
let h = 4 /*the assortment of hours i've slept*/;
print(truth(h));
The output of this program is more concise:
24.0 /the factorial of the assortment of hours i've slept*/
Meta-Comments and Meta-Meta-Comments and …
Since feedback are first-class values, feedback are furthermore explained by feedback. Obviously feedback explaining a commentary are furthermore explained by feedback which in turn are explained by feedback and so on.
| Form | Description |
|---|---|
Disclose |
a really noteworthy form |
String |
unicode strings |
Amount |
floating level numbers |
Bool |
Trustyor Spurious |
Unit |
easiest the price () |
Listing |
Lists of values |
Lists
Within the intervening time there will not be this kind of thing as a special syntax for lists, as a replace the builtin suggestions list,append,keep and uncovermust be stale to make and manipulate Lists.
Syntax
The Syntax is Expression based totally mostly.
Literals
| Form | Examples |
|---|---|
Disclose |
/this is a commentary */ |
String |
"hello" "withn slump " chars" |
Amount |
1, -1.0, 42.5 |
Bool |
Trusty, Spurious |
Unit |
() |
Grouping
(a + b) c
Blocks
{ print("hello"); print("world") }
More than one expressions might maybe furthermore be grouped with curly braces. Expressions are separated with semicolons. The semicolon after the final Expression is non-mandatory. Blocks exhaust into consideration to the price of their final expression.
Capabilities
Definition
let f = fn (arg) {
print(arg);
};
Capabilities might maybe furthermore be outlined with the keyword fnfollowed by a parenthesized list of parameters and the feature body. The braces are non-mandatory, when the body is a single expression. All suggestions are nameless and first-class.
Calling a feature
print("hello")
Nothing special right here.
Variables
Declaration
let x = 42
Variables are declared with the keyword let and desires to be initialized. Variables are lexicaly scoped. Declarations exhaust into consideration to the assigned price.
Assignment
x = 100
Assignments exhaust into consideration to the assigned price.
Unary Expressions
-a !b
Nothing queer.
Binary Expressions
a + b
Operators ordered by reducing precedence:
| Operators | Examples |
|---|---|
? |
x? |
*, -, % |
x y, x % 5 |
+, - |
x + y |
==, <, > |
x < y |
& |
x & y |
| ` | ` |
Among the finest queer operator is the conceal operator (?). Ogle First Class Comments for more facts.
The good judgment operators &and |are no longer quick circuiting.
Alter Circulation Expressions
If
if (situation) { "honest" } else { "fraudulent" }
Parenthesis spherical the situation are wanted. Braces spherical single expressions and the else branch are non-mandatory. If expressions exhaust into consideration to the price of the taken branch.
Whereas
whereas (situation) { do_something() }
Parenthesis spherical the situation are wanted. The Braces cant be unnoticed, if the body is a single expression. Whereas loops exhaust into consideration to the price of the loop body for the length of the final iteration.
Builtin Capabilities
| Just | Description |
|---|---|
print(args...) |
Print any assortment of values. When known as with a single argument, the arguments commentary is printed as successfully |
input() |
Be taught single line and return it as a string. |
str(price) |
Convert price to string. |
cmnt(price) |
Convert price to commentary. |
num(price) |
Convert string to number. Returns ()if the conversion fails. |
list(args...) |
Rating list containing the arguments. |
append(list, price) |
Append price to list |
keep(list, index, price) |
Place price into list |
uncover(list, index) |
Rating price out of list |