bobbylisp/spec.md

Specification

Syntax

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Expressions

• Literals

  A literal is a value that is written directly into the source code.

  • Number

    An number literal is of type f64 and can be expressed with or without a decimal point.

    • Examples: 1, 3.14, .5

    Number:
        Digits + (maybe '.' + Digits).
        (* Optional whole number, e.g. .5 *)
        ('.' + Digits).
    Digits:
        one or more of 0..9.
    

  • String

    A string literal can consist of zero or more characters enclosed in double quotes (")

    • Examples: "Hello, World", "They said \"Hi\"", "Foo\nBar"

    String:
        '"' + (zero or more of Character) + '"'.
    Character:
        any character except '"' or '\'.
        escape sequences.
    

  • Boolean

    A boolean literal can be either true or false.

    Boolean:
        'true' or 'false'.
    

  • Unit

    A unit literal is a value that represents the absence of a value.

    Unit:
        '()'.
    

• Identifiers

  An identifier is a name that is used to refer to a variable, function, or other entity.

  • Examples: foo, barBaz, add2

  Identifier:
      (Letter + zero or more of LetterOrDigit) but
      not any of Keywords.
  Letter:
      one of a..z or A..Z.
  LetterOrDigit:
      Letter or one of 0..9.
  

• Operators

  An operator is a symbol that is used to represent an operation.

  Binary:
      one of (
          (* Arithmetic *)
          + - * / %
          (* Comparison *)
          == != < <= > >=
          (* Logical *)
          && ||
      ).
  Unary:
      one of (- !).
  

• Application (Function Call)

  An application is an expression that calls a function with a list of arguments. It is not necessary that the callee is a function, but it must be an expression that evaluates to a function.

  Arguments:
      zero or more of Expression delimited by ','.
  Application:
      Expression + '(' + Arguments + ')'.
  

  • Examples:

    foo(1, 2, 3)
    (\x -> x + 1)(2)
    

• If-Else

  An if-else expression is an expression that evaluates to one of two expressions depending on the value of a condition.

  IfElse:
      'if' + Expression + 'then' + Expression + 'else' + Expression.
  

  • Examples:

    if true then 1 else 2
    if 1 == 2 then "foo" else "bar"
    

• Let Binding(s)

  There are 2 types of let bindings:

  • "Imperative" let bindings, which are similar to variable declarations in imperative languages (Javascript, Rust, etc.).

    Bindings:
        one or more of Binding delimited by ','.
    Let:
        'let' + Bindings.
    

    • Example:

      let x = 1 // -> ()
      x + 1     // -> 2
      

  • "Functional" let bindings, which are similar to variable declarations in functional languages (ML-family, etc.).

    LetIn:
        'let' + Bindings + 'in' + Expression.
    

    • Example:

      let x = 1, y = 2 in
          x + y // -> 3
      

• Block & Return

  A block is a sequence of expressions that are evaluated in order and the value of the last expression is returned (if not ended with a semicolon).

  A return expression is an expression that will exit the current block and return the value of the expression. It is not necessary to use a return expression in a block, but it could be useful for early termination.

  Any use of a return expression outside of a block is not allowed.

  Block:
      '{' + zero or more of Expression + '}'.
  Return:
      'return' + Expression.
  

  • Examples:

    {
        let x = 1;
        let y = 2;
        x + y
    }
    

    fun foo(): num = {
        if true then
            return 1;
    
        let bar = 42;
        bar
    };
    

Keywords

Keywords are reserved words that cannot be used as identifiers. They are used to represent constructs of the language.

Keywords:
    if then else
    let fun return