github.com/skx/monkey
This repository contains an interpreter for the "Monkey" programming language, as described in Write an Interpreter in Go.
The interpreter in this repository has been significantly extended from the starting point:
i++, i--)../monkey examples/hello.mon".)function.<= & >=.==, !=, <=, & >=.if ( a >= 'a' && a <= 'z' ) ..if ( a || b ) ..let.
+=", "-=", "*=", & "/=" to work.PI, E, STDIN, STDOUT, & STDERR.pragma("strict"); to your script, which will cause the interpreter to show a suitable error-message and terminate.function greet( name = "World" ) { puts("Hello, " + name + "\n"); }eval function.
match
if ( name ~= /steve/i ) { puts( "Hello Steve\n"); } 1..10).foreach statement.printf and sprintf primitives, which work as you would expect.
printf( "%d %s", 3, "Steve" );switch statements, with block-based case expressions.
null usage:
a = null; if ( a == null ) { .. }If you enjoyed this repository you might find the related ones interesting:
Finally I put together a couple of "complex" compilers, which convert input into AMD64 assembly language:
Due to the embedded standard-library implementation, which is implemented in monkey, you'll need to compile this project with go version 1.16beta1 or higher.
You can install from source like so:
git clone https://github.com/skx/monkey
cd monkey
go install
Alternatively you could install a binary-release, from the release page.
If you're an emacs user might also wish to install the monkey.el file, which provides syntax highlighting for monkey-scripts.
To execute a monkey-script simply pass the name to the interpreter:
$ monkey ./example/hello.mon
Scripts can be made executable by adding a suitable shebang line:
$ cat hello.mon
#!/usr/bin/env monkey
puts( "Hello, world!\n" );
Execution then works as you would expect:
$ chmod 755 hello.mon
$ ./hello.mon
Hello, world!
If no script-name is passed to the interpreter it will read from STDIN and execute that instead, allowing simple tests to be made.
NOTE: Example-programs can be found beneath examples/ which demonstrate these things, as well as parts of the standard-library.
Variables are defined using the let keyword, with each line ending with ;.
let a = 3;
let b = 1.2;
Variables may be integers, floats, strings, or arrays/hashes (which are discussed later).
Some variables are defined by default, for example:
puts( PI ); // Outputs: 3.14159..
puts( E ); // Outputs: 2.71828..
Variables may be updated without the need for let, for example this works
as you would expect:
let world = "Earth";
world = "world";
puts( "Hello, " + world + "!\n");
If you're not running with pragma("strict"); you can also declare and
use variables without the need for let, but that should be avoided as
typos will cause much confusion!
name = "Steve";
puts( "Hello, " + name + "\n");
monkey supports all the basic arithmetic operation of int and float types.
The int type is represented by int64 and float type is represented by float64.
let a = 3;
let b = 1.2;
puts( a + b ); // Outputs: 4.2
puts( a - b ); // Outputs: 1.8
puts( a * b ); // Outputs: 3.6
puts( a / b ); // Outputs: 2.5
puts( 2 ** 3 ) ; // Outputs: 8
Here ** is used to raise the first number to the power of the second.
When operating with integers the modulus operator is available too, via %.
monkey contains two builtin containers: array and hash.
An array is a list which organizes items by linear sequence. Arrays can hold multiple types.
let a = [1, 2.3, "array"];
let b = [false, true, "Hello World", 3, 3.13];
Adding to an array is done via the push function:
let a = push(a, "another");
You can iterate over the contents of an array like so:
let i = 0;
for( i < len(a) ) {
puts( "Array index ", i, " contains ", a[i], "\n");
i++
}
With the definition we included that produces this output:
Array index 0 contains 1
Array index 1 contains 2.3
Array index 2 contains array
Array index 3 contains another
As a helper you may define an array of consecutive integers via the range operator (..):
let a = 1..10;
A hash is a key/value container, but note that keys may only be of type boolean, int and string.
let a = {"name":"monkey",
true:1,
7:"seven"};
puts(a); // Outputs: {name: monkey, true: 1, 7: seven}
puts(a["name"]); // Outputs: monkey
Updating a hash is done via the set function, but note that this returns
an updated hash - rather than changing in-place:
let b = set(a, 8, "eight");
puts(b); // Outputs: {name: monkey, true: 1, 7: seven, 8: eight}
You can iterate over the keys in a hash via the keys function, or delete
keys via delete (again these functions returns an updated value rather than
changing it in-place).
Hash functions are demonstrated in the examples/hash.mon sample.
The core primitives are:
delete
int
keys
len
match
pragma
pragma("strict");.push
puts
printf
set
sprintf
string
type
The following functions are also part of our standard library, but are implemented in 100% pure monkey:
first
last
rest
In addition to the core built-in functions we also have a minimal-standard library. The library includes some string/file primitives, a regular-expression matcher, and some maths-helpers.
You can see the implementation of the go-based standard-library beneath evaluator/stdlib*, and several of these functions are documented in the various examples/.
NOTE: Parts of our standard-library are implemented in 100% pure monkey, and these are embedded in our compiled interpreter. The source of the functions can be viewed in data/stdlib.mon.
If you wish to make changes to the monkey-based standard-library you'll need to rebuild the interpreter after making your changes, to ensure they are bundled into the executable.
Nothing special is required, the following will suffice as you'd expect:
go build .
monkey uses fn to define a function which will be assigned to a variable for
naming/invocation purposes:
let add = fn(a, b) { return a + b;};
puts(add(1,2)); // Outputs: 3
// functions can be used via their variables
let addTwo = fn(a,b, f) { return 2 + f(a, b);};
puts( addTwo(1,2, add) ); // outputs: 5.
It is also possible to define a function without the use of let, via the function keyword. This was added to make the language feel more natural to C-developers:
function hello() { puts "Hello, world\n" ; };
hello(); // Outputs: Hello, world" to the console.
You may specify a default value for arguments which are not provided, for example:
let foo = fn( name = "World!") {
puts( "Hello, " + name + "\n" );
};
foo();
foo( "Steve" );
This will output what you expect:
Hello, World!
Hello, Steve
The same thing works for literal functions:
// Function with a default (string) argument
function meh( arg = "Steve" ) {
puts( "Argument:", arg, " has type:", type(arg), "\n");
};
// Call it with no argument and the default will be used.
meh();
// But of course all the rest work just fine.
meh( 1 );
meh( 1/3.0 );
meh( "Steve" );
meh( [1,2,3,4] );
meh( {"Steve":"Kemp", true:1, false:0, 7:"seven"} );
monkey supports if-else statements.
let max = fn(a, b) {
if (a > b) {
return a;
} else {
return b;
}
};
puts( max(1, 2) ); // Outputs: 2
monkey supports the use of ternary expressions, which work as you
would expect with a C-background:
function max(a,b) {
return( a > b ? a : b );
};
puts( "max(1,2) -> ", max(1, 2), "\n" );
puts( "max(-1,-2) -> ", max(-1, -2), "\n" );
Note that in the interests of clarity nested ternary-expressions are illegal!
Monkey supports the switch and case expressions, as the following example demonstrates:
name = "Steve";
switch( name ) {
case /^steve$/i {
printf("Hello Steve - we matched you via a regexp\n");
}
case "St" + "even" {
printf("Hello SteveN, you were matched via an expression\n" );
}
case 3 {
printf("Hello number three, we matched you literally.\n");
}
default {
printf("Default case: %s\n", string(name) );
}
}
See also examples/switch.mon.
monkey supports a golang-style for-loop statement.
let sum = fn(x) {
let i = 1;
let sum = 0;
for (i < x) {
sum += i;
i++;
}
return sum;
};
puts(sum(100)); // Outputs: 4950
In addition to iterating over items with the for statement, as shown above, it is also possible to iterate over various items via the foreach statement.
For example to iterate over an array:
a = [ "My", "name", "is", "Steve" ]
foreach item in a {
puts( "\t", item , "\n");
}
Here you see that we've iterated over the items of the array, we can also see their offsets like so:
foreach offset, item in a {
puts( offset, "\t", item , "\n");
}
The same style of iteration works for Arrays, Hashes, and the characters which make up a string. You can see examples of this support in examples/iteration.mon.
When iterating over hashes you can receive either the keys, or the keys and value at each step in the iteration, otherwise you receive the value and an optional index.
monkey support two kinds of comments:
// and last until the end of the line./* and */.The ++ and -- modifiers are permitted for integer-variables, for example the following works as you would expect showing the numbers from 0 to 5:
let i = 0;
for ( i <= 5 ) {
puts( i, "\n" );
i++;
}
Another feature borrowed from C allows variables to be updated in-place via the operators +=, -=, *=, & /=.
Using += our previous example could be rewritten as:
let i = 0;
for ( i <= 5 ) {
puts( i, "\n" );
i += 1;
}
The update-operators work with integers and doubles by default, when it comes to strings the only operator supported is +=, allowing for a string-append:
let str = "Forename";
str += " Surname";
str += "\n";
puts( str ); // -> "Forename Surname\n"
As with many scripting languages commands may be executed via the backtick operator (```).
let uptime = `/usr/bin/uptime`;
if ( uptime ) {
puts( "STDOUT: ", uptime["stdout"].trim() , "\n");
puts( "STDERR: ", uptime["stderr"].trim() , "\n");
} else {
puts( "Failed to run command\n");
}
The output will be a hash with two keys stdout and stderr. NULL is
returned if the execution fails. This can be seen in examples/exec.mon.
The match function allows matching a string against a regular-expression.
If a match fails NULL will be returned, otherwise a hash containing any capture groups in the match.
This is demonstrated in the examples/regexp.mon example.
You can also perform matching (complete with captures), with a literal regular expression object:
if ( Name ~= /steve/i ) { puts( "Hello Steve\n" ); }
if ( Name !~ /[aeiou]/i ) { puts( "You have no vowels.\n" ); }
// captures become $1, $2, $N, etc.
ip = "192.168.1.1";
if ( ip ~= /([0-9]+)\.([0-9]+)\.([0-9]+)\.([0-9]+)/ ) {
printf("Matched! %s.%s.%s.%s\n", $1, $2, $3, $4 );
}
The open primitive is used to open files, and can be used to open files for either reading, or writing:
// Open a file for reading
fh = open( "/etc/passwd" );
fh = open( "/etc/passwd", "r" );
// Open a file for writing
fh = open( "/tmp/blah", "w" );
// Open a file for appending
fh = open( "/tmp/blah", "wa" );
Once you have a file-object you can invoke methods upon it:
read()
readlines()
write(data)
These are demonstrated in the following examples:
By default three filehandles will be made available, as constants:
STDIN
STDOUTSTDERR
The primitive stat will return a hash of details about the given file, or
directory entry.
You can change the permissions of a file via the chmod function, but note that the second argument is an octal string:
chmod( "/tmp/evil.sh", "755")
chmod( "/tmp/normal", "644")
To remove a file, use unlink:
unlink( "/tmp/trash.txt" )
And finally to make a directory:
mkdir( "/tmp/blah" );
There is now support for "object-methods". Object methods are methods
which are defined against a type. For example all of our primitive
types allow a methods() method, which returns the methods which are
available against them.
Similarly each of them implement a type() function which returns the
type involved:
let i = 1;
puts( i.type() );
let s = "Steve";
puts( s.type() );
Or even:
puts( "Steve".type() );
Seeing methods available works as you would expect:
a = [ "Array", "Is", "Here" ];
let i = 0;
for ( i < len(a.methods() ) ) {
puts( "Method " + a.methods()[i] + "\n" );
i++;
}
This shows:
Method find
Method len
Method methods
Method string
The string object has the most methods at the time of writing, but
no doubt things will change over time.
The object-methods mentioned above are implemented in Go, however it is also possible to define such methods in 100% monkey!
You can define a method via something like:
function string.steve() {
puts( "Hello, I received '", self, "' as an argument\n" );
}
Note that the function has access to the object it was invoked upon via the
implicit self name. Invocation would look as you expect:
let s = "Hello, world";
s.steve(); -> Hello, I received 'Hello, world' as an argument
You can see data/stdlib.mon implements some primitives
in this fashion, for example the functional-programming methods array.map,
array.filter, string.toupper, etc, etc.
This repository is configured to run tests upon every commit, and when pull-requests are created/updated. The testing is carried out via .github/run-tests.sh which is used by the github-action-tester action.
Releases are automated in a similar fashion via .github/build, and the github-action-publish-binaries action.
Fuzz-testing involves creating random input, and running the program to test with that, to see what happens.
The intention is that most of the random inputs will be invalid, so you'll be able to test your error-handling and see where you failed to consider specific input things.
The 1.18 release of the golang compiler/toolset has integrated support for fuzz-testing, and you can launch it like so:
go test -fuzztime=300s -parallel=1 -fuzz=FuzzMonkey -v
Sample output looks like this:
$ go test -fuzztime=300s -parallel=1 -fuzz=FuzzMonkey -v
=== RUN FuzzMonkey
fuzz: elapsed: 0s, gathering baseline coverage: 0/240 completed
fuzz: elapsed: 0s, gathering baseline coverage: 240/240 completed, now fuzzing with 1 workers
fuzz: elapsed: 3s, execs: 4321 (1440/sec), new interesting: 6 (total: 246)
fuzz: elapsed: 6s, execs: 4321 (0/sec), new interesting: 6 (total: 246)
cfuzz: elapsed: 9s, execs: 4321 (0/sec), new interesting: 6 (total: 246)
fuzz: elapsed: 12s, execs: 4321 (0/sec), new interesting: 6 (total: 246)
fuzz: elapsed: 15s, execs: 4321 (0/sec), new interesting: 6 (total: 246)
fuzz: elapsed: 18s, execs: 4321 (0/sec), new interesting: 6 (total: 246)
fuzz: elapsed: 21s, execs: 4321 (0/sec), new interesting: 6 (total: 246)
fuzz: elapsed: 24s, execs: 4321 (0/sec), new interesting: 6 (total: 246)
fuzz: elapsed: 27s, execs: 73463 (23060/sec), new interesting: 17 (total: 257)
fuzz: elapsed: 30s, execs: 75639 (725/sec), new interesting: 18 (total: 258)
fuzz: elapsed: 33s, execs: 125712 (16701/sec), new interesting: 25 (total: 265)
fuzz: elapsed: 36s, execs: 139338 (4543/sec), new interesting: 34 (total: 274)
fuzz: elapsed: 39s, execs: 173881 (11511/sec), new interesting: 49 (total: 289)
fuzz: elapsed: 42s, execs: 198046 (8055/sec), new interesting: 55 (total: 295)
fuzz: elapsed: 45s, execs: 210203 (4054/sec), new interesting: 75 (total: 315)
fuzz: elapsed: 48s, execs: 262945 (17580/sec), new interesting: 85 (total: 325)
fuzz: elapsed: 51s, execs: 297505 (11517/sec), new interesting: 108 (total: 348)
fuzz: elapsed: 54s, execs: 308672 (3722/sec), new interesting: 116 (total: 356)
fuzz: elapsed: 57s, execs: 341614 (10984/sec), new interesting: 123 (total: 363)
fuzz: elapsed: 1m0s, execs: 366053 (8146/sec), new interesting: 131 (total: 371)
fuzz: elapsed: 1m3s, execs: 396575 (10172/sec), new interesting: 137 (total: 377
...
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