package jane_rope

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String representation with cheap concatenation.







Published: 14 Jun 2023



A rope is a standard data structure that represents a single string as a tree of strings, allowing concatenation to do no work up front.

That is, a string formed by many Rope concatenations followed by a to_string needs only copy each input to the output once, whereas a string expression looking like a ^ b ^ c ^ ... ^ z must create an intermediate string for every concatenation, and will copy the original data into and out of short-lived temporary strings many times.

On the other hand, because String.concat [ s1; s2; s3; ... ] allocates a single string and copies the inputs into it, Rope is no improvement over that usage. Rope becomes useful when the construction of the sequence of strings is more complex -- a good example is prettyprinting an expression language, where you need to parenthesize subexpressions (appending a short string at both ends) and handle infix binary operators (appending two long strings both made up of many parts, with a short string in between).

Any operations that would produce a Rope longer than String.max_length raise instead. They are not marked with _exn on their names since (at least on 64-bit) this number is far in excess of the size of your memory, so isn't likely to come up in practice.

A more fully-featured implementation of the same idea is available in the zed library.

Dependencies (4)

  1. dune >= "2.0.0"
  2. ppx_jane >= "v0.16" & < "v0.17"
  3. base >= "v0.16" & < "v0.17"
  4. ocaml >= "4.14.0"

Dev Dependencies


Used by (2)

  1. re2 >= "v0.16.0"
  2. shuttle_http >= "0.10.0"