Strings are indexed by String.Pos, which internally records byte countsrather than character counts, and thus takes constant time. String.Posincludes a proof that the byte count in fact points at the …

Lean 4 programming language and theorem prover. Contribute to leanprover/lean4 development by creating an account on GitHub.

Mar 31, 2025 · My question is: Is it possible to do this in Lean 4, and parse a string as Lean code? I understand that Lean's syntax is influenced by the current context/state (e.g. the notation 's and type …

Converts a list into a string, using ToString.toString to convert its elements. The resulting string resembles list literal syntax, with the elements separated by ", " and enclosed in square brackets. …

Dec 15, 2025 · Parser and Syntax Relevant source files Purpose and Scope This page documents Lean 4's parser system, which converts source text into concrete syntax trees (Syntax). The parser is a …

Jul 31, 2023 · As Moritz Firsching points out, Lean4 defines a String.toNat which will return a Option Nat. Because of that you have also to adapt your code to handle the possibility of failure in the conversion:

Attempts to convert a float to a JsonNumber, if the number isn't finite returns the appropriate string from "NaN", "Infinity", "-Infinity". Equations Instances For

Parser Combinator Library for Lean 4. Contribute to fgdorais/lean4-parser development by creating an account on GitHub.

Converts a list into a string, using ToString.toString to convert its elements. The resulting string resembles list literal syntax, with the elements separated by ", " and enclosed in square brackets.

May 22, 2025 · 0 This is a follow-up question to How to parse the content of a string as Lean 4 code? . I am trying to increase my use of Lean 4 by writing a REPL that (just like Haskell's hint package) can …