imp's Introduction

Imp

This is a simple imperative language for learning/teaching Haskell.

The documents are written in Japanese.

The implementation is about 400 lines.

Example

// comment
var x = 0;                // declare variable, number literal
var f = fun(x, y) {       // function literal
  return x + y;           // return statement
};
if (x != 0) {             // if statement (not expression)
  print("assert false\n"); // print, string literal
} else {
  while (x < 10) {        // while statement
    x = x + 1;            // assignment
  }
  print(f(x, 10));         // function application
}

Types

number
boolean
string

Operators

(==), (!=) : 'a -> 'a -> boolean
(&&), (||) : boolean -> boolean -> boolean
(+), (-), (*), (/) : number -> number -> number
(<), (<=), (>), (>=) : number -> number -> boolean
(++) : string -> string -> string

BNF

<toplevel> ::= <statement>*

<statement> ::= var <identifier> = <expression>;
              | <identifier> = <expression>;
              | if (<expression>) { <statement>* } else { <statement>* }
              | while (<expression>) { <statement>* }
              | return <expression>;
              | <expression>;

<expression> ::= <constant>
               | fun(<identifiers>) { <statement>* }
               | <expression> <operator> <expression>
               | <expression>(<expressions>)
               | <identifier>

<expressions> ::= <expression>, <expression>, ..., <expression>

<identifiers> ::= <identifier>, <identifier>, ..., <identifier>

<constant> ::= <integer or float>
             | true | false
             | " <any char without ">* "

<identifier> ::= [a-z][a-zA-Z_0-9'!?]*

<operator> ::= == | !=
             | && | ||
             | + | - | * | /
             | < | <= | > | >=
             | ++