Error Handling

Error Handling

What you'll learn

This guide covers try, except, finally, raise, file-oriented with, and how to read LP parser and codegen diagnostics.

Prerequisites

• Read Language Basics first.

Syntax And Concepts

Raising an exception

LP supports string-based raise expressions:

raise "something went wrong"

try, except, and finally

Basic structure:

try:
    risky_call()
except:
    print("handled")
finally:
    print("cleanup")

The current runtime uses a generic exception mechanism. Typed except SomeType as err: syntax is parsed, but the current code generation path treats exception handling generically.

with for file handles

LP supports with statements around file handles returned by open().

with open("notes.txt", "w") as f:
    f.write("hello\n")

The generated C code closes the file automatically at the end of the block.

File operations

The current public file surface is:

• open(path, mode)
• file.read()
• file.write(data)
• file.close()

Reading parser diagnostics

LP's parser error output is designed to show:

• the main error message
• nearby source lines
• a highlighted error line
• hints for common mistakes such as missing colons or missing indentation

Examples

Raise and catch

def main():
    try:
        raise "broken"
    except:
        print("handled")
    finally:
        print("done")

main()

with and file I/O

def main():
    with open("notes.txt", "w") as f:
        f.write("LP\n")

    with open("notes.txt", "r") as f:
        text = f.read()

    print(text)

main()

What a syntax failure usually means

def main()
    print("missing colon")

Expected outcome:

• LP should reject the file.
• The compiler should show the offending line and a hint about the missing colon.

Common errors and limitations

• except SomeType as err: is parsed, but current exception handling is generic. Do not depend on typed exception objects yet.
• with is currently documented for file handles from open(). Treat arbitrary context-manager semantics as unsupported.
• yield exists in the lexer and AST, but it is not documented as a stable public language feature yet.
• If you get expected indented block, add an indented body or use pass.
• If you get expected ':', inspect the end of the preceding control-flow or declaration line.

See also

• Runtime Modules
• CLI and Tooling
• Troubleshooting
• Language Reference