SimpLang - A Simple Language

All values are signed 64 bit integers. All global definitions are functions. Calls are not tail recursive. All functions return values. Functions are not first class.

Some pieces in the language grammar, like end, are superfluous. They are there to make parsing and later extension easier.

Example program

let fac n =
	loop acc = 1 and
		 i = 2
	in
		if n < i then
    		acc
  		else
			recur (acc * i) (i + 1)
		end
	end
end

let main n =
	fac (n)
end

Control constructs

let introduces variable bindings. They are only visible within the right hand sides of later bindings in the same let expression and the body of the let expression. Later bindings can hide earlier ones:

let a = 1 and
	b = a + 1
in
	b
end

gives 2.

let a = 31415
in
	let a = 1 and
		a = a + 1
	in
		a
	end
end

also gives 2, because the first a in the inner let hides the outer a.

if works as expected. It must have both then and else clauses.

loop introduces variable bindings like let, but it also provides a jump target for uses of recur in the body. recur invocations jump to the innermost loop containing that recur, giving new values to the bound variables.

recur is only legal within a loop and can only occur in a tail position, i.e., where the continuation is the same as the continuation of the containing loop. In particular, a recur can never be the condition of an if, an argument in a function call, an operand to an operator, the right hand side of a let or loop binding.

Functions can only be used in their own definitions or in later definitions. All functions must have different names.

All arguments to function calls and recur must be parenthesized, i.e.,

recur (a) (-b)

is legal, while

recur a -b

is not.

Values

if and all logical operators consider 0 to be false, all other values to be true. Logical operators return 0 for false and 1 for true.

Operators

These are all the operators, in increasing order of precedence:

&&, ||
!
<, ==
+
*
- (unary)
function application

&& and || are logical operators, using shortcut evaluation. That means && will not evaluate its right hand side if the left hand side evaluates to 0, and || will only evaluate its right hand side if its left hand side evaluates to 0.

Miscellaneous

Functions must take at least one argument.

Syntax

Identifiers can contain only letters, digits, and the underscore, but cannot start with a digit.

Function calls use ML/Haskell syntax: Function name followed by arguments.

Tests

Run the testsuite with

./tests/test.py TEST-SUITE YOUR-EXE [YOUR-EXE-ARG ...]

where TEST-SUITE is the name of one of the directories in tests, such as full.