9. pyxc: File Input Mode

9.1 Add Shared Input State

Add:

static FILE *Input = stdin;
static bool IsRepl = true;

Input identifies the character source. IsRepl controls presentation only: prompts and “Parsed...” chatter belong to an interactive session, not normal script output.

9.2 Route Every Character Read through Input

In advance(), replace:

getchar()

with:

fgetc(Input)

Replace newline lookahead reads the same way, and change:

ungetc(NextChar, stdin)

to:

ungetc(NextChar, Input)

This is the only lexer change required. Tokens, locations, diagnostics, parsing, codegen, optimization, and JIT execution remain shared.

9.3 Add the Positional Input Option

Near the existing LLVM command-line options, add:

static cl::opt<string> InputFile(
    cl::Positional, cl::desc("[script.pyxc]"),
    cl::init(""), cl::cat(PyxcCategory));

This accepts zero or one positional filename:

no filename -> REPL
filename    -> file mode

9.4 Add Optional IR Output

Chapter 8 always prints generated IR. Add:

static cl::opt<bool> VerboseIR(
    "v", cl::desc("Print generated LLVM IR to stderr"),
    cl::init(false), cl::cat(PyxcCategory));

Wrap every successful IR dump:

if (VerboseIR)
  FunctionIR->print(errs());

This makes normal program output usable while retaining an inspection mode:

./build/pyxc -v program.pyxc

Keep IR on stderr; runtime output remains on stdout.

9.5 Open the Selected Input

Extend ProcessCommandLine() after parsing and optimization-level validation:

if (!InputFile.empty()) {
  Input = fopen(InputFile.c_str(), "r");
  if (!Input) {
    perror(InputFile.c_str());
    return -1;
  }
  IsRepl = false;
} else {
  IsRepl = true;
}

return 0;

Use perror() so a missing file includes the operating system's explanation.

Do this before priming the lexer. getNextToken() must read its first character from the selected stream.

9.6 Centralize REPL-Only Output

Add:

void PrintReplPrompt() {
  if (IsRepl) {
    fflush(stdout);
    fprintf(stderr, "ready> ");
  }
}

Replace direct prompt printing with PrintReplPrompt().

Add a REPL-only logging helper:

void Log(const string &Message) {
  if (IsRepl)
    fprintf(stderr, "%s", Message.c_str());
}

Replace confirmation messages such as:

fprintf(stderr, "Parsed a function definition.\n");

with:

Log("Parsed a function definition.\n");

Do the same for externs and top-level expressions.

Do not suppress diagnostics. Syntax, codegen, and file-opening errors must still be printed in both modes.

9.7 Keep Evaluation Output Explicit

Use one result function:

void PrintEvaluationResult(double Result) {
  fprintf(stdout, "Evaluated to %f\n", Result);
}

Call it after executing a top-level anonymous expression.

This is program behavior, not parser chatter. Runtime functions such as printd and putchard also continue writing normally.

9.8 Close the File

After MainLoop() returns, add:

if (Input && Input != stdin) {
  fclose(Input);
  Input = stdin;
}

Do not close stdin.

9.9 Build and Run the REPL

cmake -S . -B build \
  -DLLVM_DIR="$(llvm-config --cmakedir)"
cmake --build build
./build/pyxc

Try:

ready> 1 + 2

Expected:

Parsed a top-level expression.
Evaluated to 3.000000

The REPL behavior should be unchanged except that IR is hidden unless -v is present.

9.10 Run a Source File

Create or use a test file such as:

extern def printd(x)
def square(x): x * x
printd(square(5))

Run:

./build/pyxc program.pyxc

Expected runtime output:

25.000000
Evaluated to 0.000000

There should be no ready> prompt and no “Parsed...” messages.

Inspect the same run with IR:

./build/pyxc -v program.pyxc

Redirect the streams independently when useful:

./build/pyxc -v program.pyxc >program.out 2>program.ll

9.11 Test the Error Boundary

Run a missing file:

./build/pyxc does-not-exist.pyxc

Expected behavior:

does-not-exist.pyxc: <operating-system error>

and a nonzero exit code.

Run the full suite:

llvm-lit -v test/

What you built is one compiler with two input presentations:

REPL mode -> stdin + prompts + confirmations
file mode -> file  + quiet compiler presentation
both      -> same lexer/parser/codegen/optimizer/JIT

Next: Chapter 10 adds comparisons, if expressions, and for loops.

9.12 Need Help?

Build issues? Questions?

• Report a problem with GitHub Issues
• Ask a question in GitHub Discussions

Include:

• Your operating system and version
• The chapter number
• The exact command you ran
• The complete error message
• The output of c++ --version and cmake --version
• The output of llvm-config --version for Chapter 6 and later