Been making an MLElixir thing (not released yet…) for fun in spare time in the past day. I’m just trying to see how much I can get an ML-traditional syntax entirely within the Elixir AST, while being properly typed (with occasional fun with Refined Types and such). An example IEX session with it:

• Basic Types (adding more over time)

iex> import MLElixir
MLElixir
iex> defml 1
1
iex> defml 6.28
6.28
iex> defml :ok
:ok

• Let untyped variable bindings:

iex> defml let _a = 2 in 1
1
iex> defml let a = 1 in a
1
iex> defml let a = 42 in
...> let b = a in
...> let c = b in
...> c
42

• Let Typed variable bindings (The errors are very simplistic and not descriptive right now, still debugging time after all):

iex> defml let ![a: int] = 1 in a
1
iex> defml let ![a: float] = 6.28 in a
6.28
iex> defml let a = 1 in
...> let ![b: int] = a in
...> b
1
iex> defml let ![a: int] = 6.28 in a
** (MLElixir.UnificationError) Unification error between `{:"$$TCONST$$", :float, [values: [6.28]]}` and `{:"$$TCONST$$", :int, []}` with message:  Unable to resolve mismatched types
    (typed_elixir) lib/ml_elixir.ex:566: MLElixir.resolve_types!/3
    (typed_elixir) lib/ml_elixir.ex:250: MLElixir.resolve_binding/3
    (typed_elixir) lib/ml_elixir.ex:163: MLElixir.parse_let/3
    (typed_elixir) expanding macro: MLElixir.defml/1
                   iex:16: (file)

• Let Refined Typed variable bindings:

iex> defml let ![a: int a=1] = 1 in a
1
iex> defml let ![a: int a<=2] = 1 in a
1
iex> defml let ![a: int a>=2] = 1 in a
** (MLElixir.UnificationError) Unification error between `{:"$$TCONST$$", :int, [values: [1]]}` and `{:"$$TCONST$$", :int, [values: [{2, :infinite}]]}` with message:  Unable to resolve
    (typed_elixir) lib/ml_elixir.ex:566: MLElixir.resolve_types!/3
    (typed_elixir) lib/ml_elixir.ex:250: MLElixir.resolve_binding/3
    (typed_elixir) lib/ml_elixir.ex:163: MLElixir.parse_let/3
    (typed_elixir) expanding macro: MLElixir.defml/1
                   iex:6: (file)

Function calls (shown here via +):

iex> defml 1+2
3
iex> defml 1.1+2.2
3.3000000000000003
iex> defml 1+2.2
** (MLElixir.UnificationError) Unification error between `{:"$$TCONST$$", :int, [values: [1]]}` and `{:"$$TCONST$$", :float, [values: [2.2]]}` with message:  Unable to unify types
    (typed_elixir) lib/ml_elixir.ex:712: MLElixir.unify_types!/3
    (typed_elixir) lib/ml_elixir.ex:108: anonymous fn/3 in MLElixir.Core.__ml_open__/0
    (typed_elixir) lib/ml_elixir.ex:199: MLElixir.parse_ml_expr/2
    (typed_elixir) lib/ml_elixir.ex:145: MLElixir.defml_impl/2
    (typed_elixir) expanding macro: MLElixir.defml/1
                   iex:2: (file)

Opening (‘import’ in Elixir parlance) another module (also showing how to disable the Core opens, as you can see it is the Core that defines the + function):

iex> defml let open MLElixir.Core in 1+2
3
iex> defml no_default_opens: true, do: let open MLElixir.Core in 1+2
3
iex> defml no_default_opens: true, do: 1+2
** (MLElixir.InvalidCall) 6:Invalid call of `+` because of:  No such function found
    (typed_elixir) lib/ml_elixir.ex:196: MLElixir.parse_ml_expr/2
    (typed_elixir) lib/ml_elixir.ex:145: MLElixir.defml_impl/2
    (typed_elixir) expanding macro: MLElixir.defml/1
                   iex:6: (file)