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FScript REPL Guide

The FScript CLI starts an interactive REPL when you run fscript with no script path and no redirected stdin.

Start

fscript

If you are running from source:

./src/FScript/bin/Debug/net10.0/fscript

Prompts

  • > means a new top-level input.
  • . means the REPL is waiting for more lines for the current input.

Input and execution model

  • The REPL tries to parse/evaluate after each entered line.
  • If the input is syntactically incomplete, it keeps buffering lines.
  • For multiline blocks, submit with an extra blank line after your block (double-Enter while pending).
  • On successful execution, expression results are printed.
  • If the result is a function value, the REPL prints a typed signature (for example (x: int) -> int) instead of an opaque closure value.

Session state

  • Top-level definitions (let, type declarations, etc.) are retained and available in later inputs.
  • Pure expression entries are evaluated and printed, but are not retained as top-level declarations unless bound with let.

Errors

  • Type and evaluation errors are reported immediately and the pending buffer is reset.
  • Parse errors for incomplete input are deferred while you are still typing. If you force submission (double-Enter on pending input), parse errors are reported.

Exit

  • Ctrl+D (EOF) exits the REPL. If there is pending input, the REPL attempts to run it first.
  • Ctrl+C exits immediately.

Root directory and imports

Set the sandbox/import root with -r/--root:

fscript -r /path/to/project

This affects path resolution for import and runtime filesystem extern behavior.

Mode selection notes

  • fscript <script.fss> runs file mode.
  • cat script.fss | fscript runs stdin mode.
  • fscript (no file, no redirected stdin) runs REPL mode.