Boar lang 🐗

                  #         
          # # # # # #       
      # # #         #       
    # #             # # #   
    #                 # # # 
    # #   # # #   # # # #   
    # # # # # # # # #       
    # # #     # # # #       

Language interpreter for a toy programming, built in Go

Details

Based on "Writing An Interpreter In Go" by Thorsten Ball with some extra improvements, such as:

• The ability to read and evaluate .br code files (or trigger the REPL using --prompt)
• Additional built in functions for the Hash and Array objects (inspired from other languages such as Ruby)
• Standard Object#Function invocation: someObject.someMethod() as opposed to someMethod(someObject)
• Variable reassignment (let x = 3; x = "hello" as opposed to let x = 3; let x = "hello")
• Index reassignment for Arrays and Hashes (hash[key] = expression, arr[index] = expression)
• For loops
• Improved REPL:
  • evaluate multiple lines
  • user input history
  • syntax highlighting
  • helpful suggestions
  • exit typing exit()
• Base project refactors
• Additional dev notes for each interpreter component

Quick Start Guide:

The recommended way is to use Docker:

git clone git@github.com:CryptoRodeo/boar-lang.git

cd ./boar-lang

docker build . -t boar-lang

docker run -it --name="boar-lang" boar-lang

# To start the prompt type './boar --prompt'
$ ./boar --prompt
Hello boar, (type 'exit()' to exit)
~> 

# running an .br file (a test file exists)
$ ./boar -f ./test.br

You can also just run it regularly (requires go version >= 1.16):

# Build executable
go build -o boar

# Running the prompt
$ ./boar --prompt

Hello kilgore, (type 'exit()' to exit)
~> 

# Running a .br file (a test file exists)
$ ./boar -f ./test.br

Language Features:

Basic math operations:

~> 5 + 5
10

~> 8 * 2
16

~> (1 > 2) == false
true

~> !true
false

Conditional expressions:

~> if (1 > 2) { "a" } else { "b" }
b

Evaluating boolean expresisons:

~> 1 < 2
true
~> true == false
false

dynamic typing:

~> let x = 2
~> x
2

~> x = "hello"
~> x
hello

string concatenation:

~> "Hello" + " " + "World"
Hello World

Error handling:

~> let x

🐗 Error!:
> expected next token to be =, got EOF instead

~> let arr = [1,2 

🐗 Error!:
> expected next token to be ], got EOF instead

~> 

functions:

~> let adder = fn(a,b) { a + b }
~> adder(2,3)
5
~> fn(x) { x * 2; }(2)
4

closures

~> let newAdder = fn(x) { fn(y) { x + y } };
~> let addTwo = newAdder(2);
~> addTwo(3);
5
~> let addThree = newAdder(3);
~> addThree(5)
8

first class functions

~> let add = fn(a, b) { a + b };
~> let sub = fn(a, b) { a - b };
~> let applyFunc = fn(a, b, func) { func(a, b) };
~> applyFunc(2, 2, add);
4
~> applyFunc(10, 2, sub);
8

For loops

~> let y = 0;
~> for (let x = 0; x < 10; x = x + 1) { y = x; };
~> y
9

~> for (let a = 0; a < 5; a = a + 1) { puts(a); }
0
1
2
3
4

Arrays:

#Creating an array
~> let x = [1,2,3]
~> x
[1, 2, 3]

#Adding to the array
~> let y = push(x,4)
~> y
[1, 2, 3, 4]

#Array::len
~> len(y)
4
~> len(x)
3
#Array::len alternative
~> y.len()
4

#Array::first
~> x.first()
1

#Array::last
~> y.last()
4

#Array::[]
~> x[2]
3

#Array index assignment
~> x[2] = "Hello!"
Hello!
~> x
[1, 2, Hello!]

#Array::map
~> let arr = [1,2,3]
~> let addTwo = fn(x) { x + 2; }
~> let res = arr.map(addTwo)
~> res
[3, 4, 5]

#Array::pop
~> let arr = [1,2,3]
~> let popVal = arr.pop()
~> arr
[1, 2]
~> popVal
3

#Array::shift
~> let tb = ["Tom", "Bombadil"]
~> let firstName = tb.shift()
~> firstName
Tom
~> tb
[Bombadil]

#Array::slice
~> let animals = ["ant", "bison", "camel", "duck", "elephant"];
~> animals.slice(2)
[camel, duck, elephant]
~> animals.slice(2, 4)
[camel, duck]
~> animals.slice()
[ant, bison, camel, duck, elephant]

Hash Maps:

#Creating a hash
~> let person = { "name": "John", "age": (2*15) }
~> person
{age: 30, name: John}

#Hash::[]
~> person["name"]
John
~> person["age"]
30

#Hash Index/Key assignment
~> let USDrinkingAge = 21
~> person["age"] = USDrinkingAge
21
~> person["age"]
21

#Hash::valuesAt
~> person.valuesAt("age", "name")
[21, John]

#Hash::toArray
~> person.toArray()
[name, John, age, 21]

#Hash::delete
~> person.delete("age")
{name: John, null: null}
~> person["age"]
null

#Hash::dig
~> let person = { "name": "Tom Bombadil", "clothes": { "shoes": "yellow boots" } };
~> person.dig("clothes", "shoes")
yellow boots

Implementation Details:

• This interpreter uses a tree-walking strategy, starting at the top of the AST, traversing every AST Node and then evaluating its statement(s)
• The parser uses the Vaughan Pratt parsing implementation of associating parsing functions with different token types as well as handling different precedence levels.