https://github.com/schani/simplang

A very simple programming language for teaching interpreter and compiler building.
https://github.com/schani/simplang

Last synced: 24 days ago
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A very simple programming language for teaching interpreter and compiler building.

• Host: GitHub
• URL: https://github.com/schani/simplang
• Owner: schani
• Created: 2014-03-31T16:58:29.000Z (over 10 years ago)
• Default Branch: master
• Last Pushed: 2017-06-29T23:15:16.000Z (over 7 years ago)
• Last Synced: 2024-08-03T18:14:44.398Z (3 months ago)
• Language: C
• Size: 88.9 KB
• Stars: 14
• Watchers: 4
• Forks: 9
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
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`.