Implement `input(prompt)`

[kmr-srbh]

@Shaikh-Ubaid , there is a small issue occurring here. Because we are directing calls to FileRead, input() itself is not having a return type and value. So, an expression like n: i32 = i32(int(input("Enter a number: ")))) leads to an exception. A simple program:

name: str = input("Your name: ")
print("Hello,", name)

gives the following output

(base) saurabh-kumar@Awadh:~/Projects/System/lpython$ ./src/bin/lpython ./examples/example.py
Your name: Segmentation fault (core dumped)

I request you to see if the implementation is correct. Instead of a separate function create_Input() with a call inside if (call_name == "input"), I am using the complete piece of code here.

[Shaikh-Ubaid]

@kmr-srbh the following works:

% cat examples/expr2.py 
name: str = "                "
name = input("Your name: ")
print("Hello,", name)
% python examples/expr2.py
Your name: John
Hello, John
% lpython examples/expr2.py
Your name: John
Hello,John

We just needed name to have initial length/space so that we could write to it the string read from stdin.

[Shaikh-Ubaid]

We need to see what other better alternative approaches can be for the workaround (for name length) in https://github.com/lcompilers/lpython/pull/2655#issuecomment-2059840977.

[kmr-srbh]

We need to see what other better alternative approaches can be for the workaround (for name length) in #2655 (comment).

You are right @Shaikh-Ubaid. How do we go about working a fix for the return type issue? This is a real problem. I am new to this area of the code-base and learning.

[certik]

Let's modify the semantics of the FileRead ASR node: if the "value" expr argument is an allocatable string, then the backend (LLVM/WASM, etc.) implementation of the FileRead node will allocate the string to hold the whole input, and assign it to it.

[kmr-srbh]

Let's modify the semantics of the FileRead ASR node: if the "value" expr argument is an allocatable string, then the backend (LLVM/WASM, etc.) implementation of the FileRead node will allocate the string to hold the whole input, and assign it to it.

@certik Do you mean handling String_t here?

https://github.com/lcompilers/lpython/blob/fce0b35fd59ba3e4a4cb978aab69ec3ff0a7a82a/src/libasr/codegen/asr_to_llvm.cpp#L7493-L7510