While nimpylib(repo) is handy to write Python code in Nim,

what if writing polyglot code, which is runnable in both Nim and Python?

An example (NPython’s test_decimalAndSpace.nim) using such polyglot

How to

We simply write two parts:

• run in both languages (thanks to their similar syntax)
• snippets run in only one, ignored by another

Many parts of syntax of they two are similar, so we don’t discuss such here

and what’s more important is that how to make some code ignored by specified one language

Cheat Nim to ignore some Python code

Let’s start with the easier one.

#[
<Python code here>
[
]#

Explain

Python regards it as:

• Comment [
• <Python code here>
• An empty list literal []
• Comment <empty>

But in Nim #[ starts a multiline comment and ]# ends it.

Restriction

No more needed to mention but the restriction is <Python code here> cannot contain ]#.

If any, simply rewrite as ] # like [1,2,3] # xxx

Cheat Python to ignore some Nim code

This part is harder.

I’d like to give my solution:

steps

"""\""".`!=`("").assert
<Nim code here>
discard "" != """"_"""

You can also use assert over discard on the last line, which is easier to remember.

Restriction

The only restriction is that <Nim code here> cannot contain """.

If any, …consider to split into single line string literals.

Explain

This trick takes advantage of some difference between Nim and Python when parsing multiline string literal node.

Here are their parsing results:

Nim:

->

assert "" != ('\\' & '"')
<Nim code here>
discard "" != ('\\' & '_')

dumpTree:

  Command
    Ident "assert"
    Infix
      Ident "!="
      StrLit ""
      TripleStrLit  "\\\""  # `\"`
  <Nim code here>
  DiscardStmt
    Infix
      Ident "!="
      StrLit ""
      TripleStrLit  "\"_"   # `\_`

Python:

->

"""\""".`!=`("").assert
<Nim code here>
discard "" != """ "_" ""

->

"""\""".`!=`("").assert
<Nim code here>
discard "" != _"""

->

'''""".`!=`("").assert
<Nim code here>
discard "" != _'''