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Egel Language v0.0.2

I wrote a little toy language you now can read an introduction to. I fully blame LtU for getting me interested in hacking around languages so don't laugh, it's embarrassing enough as it is. You can try a small Conway's Game of Life example on TIO.

Anyway, just a short heads up. It's a small language based on untyped eager combinatorial rewriting of a DAG in C++, which isn't too fast.

You're all invited to break the thing, I am at version 0.0.2 and I want to get rid of possible bugs so your expertise can matter.

Anyway, leave your comment here. Preferably, a nice one.

By marco at 2018-03-22 14:52 | LtU Forum | previous forum topic | next forum topic | other blogs | 3684 reads

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Doesn't look bad. You may

Doesn't look bad. You may want to give it a formal syntax and semantics, or at least to provide more explanations. E.g., when constants "combine", what is the type/kind of the result? Can "data" introduce only nullary constructors/constants? Is there a difference between multiple "data" and a single one with the union of their constants?

By Andris Birkmanis at Thu, 2018-03-22 18:18 | login or register to post comments

Oh right..

The formal syntax is that of an untyped lambda calculus with constants. Well, where the abstraction is a pattern-matching one. I didn't want to bore people with math in the introduction, it isn't written as an academic paper.

The type of composing terms is term. It's all untyped, I don't have a better answer than that.

By marco at Thu, 2018-03-22 18:32 | login or register to post comments

Untyped!=unstructured

Even without static types you still have some well-defined cases of how to construct (and thus deconstruct) values. I guess those are:
1. Constants
2. Compositions of values
For patterns it's probably the same plus variables:
0. Variables
1. Constants
2. Compositions of patterns
And to pattern-match a composition (value) you have to provide a composition (pattern) with the same number of components? Or do you have some kind of varargs pattern matching in mind?

By Andris Birkmanis at Fri, 2018-03-23 17:10 | login or register to post comments

You have to experiment a bit

The grammar for the LC is pretty straightforward and everything else follows from that. I never claimed it is unstructured.

You have to experiment a bit with the calculus to see how varargs can be implemented.

def sum = [ X Y -> sum (X+Y) | X -> X ]

"sum 1 2 3" roughly corresponds to

sum 1 2 3 = sum (1+2) 3 = sum (1+2+3) = 1+2+3 = 6

It's an exploitable feature which is a consequence of the reduction strategy.

By marco at Fri, 2018-03-23 22:12 | login or register to post comments

atomic strings?

What can you do with strings other than exact match and print?

By dmbarbour at Fri, 2018-03-23 20:51 | login or register to post comments

It's not documented very well, yet

Strings are Unicode objects roughly taken from libicu. I lifted the most common operations from them but you'll need to read the source code for now. (toUpper, charAt, etc..)

Apart from that I implemented pack/unpack primitives to convert from/to a list of codepoints.

It's all very rudimentary at the moment.

By marco at Fri, 2018-03-23 21:46 | login or register to post comments