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Improve the ropes module (nim-lang#17145)
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* Improve ropes module

Improve wording
Update runnableExamples
Add index bound check for `[]`
Minor format changes

* Update tests/stdlib/tropes.nim

Run on C & JS target
Test in VM
Add tests for `[]`
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@konsumlamm @ringabout
konsumlamm authored and ringabout committed Mar 22, 2021
1 parent 9260091 commit e848749
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Showing 2 changed files with 130 additions and 117 deletions.
110 changes: 47 additions & 63 deletions lib/pure/ropes.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -8,16 +8,16 @@
#

## This module contains support for a `rope`:idx: data type.
## Ropes can represent very long strings efficiently; especially concatenation
## Ropes can represent very long strings efficiently; in particular, concatenation
## is done in O(1) instead of O(n). They are essentially concatenation
## trees that are only flattened when converting to a native Nim
## string. The empty string is represented by `nil`. Ropes are immutable and
## subtrees can be shared without copying.
## Leaves can be cached for better memory efficiency at the cost of
## runtime efficiency.

include "system/inclrtl"
import streams
include system/inclrtl
import std/streams

{.push debugger: off.} # the user does not want to trace a part
# of the standard library!
Expand All @@ -29,8 +29,8 @@ var
cacheEnabled = false

type
Rope* = ref RopeObj ## empty rope is represented by nil
RopeObj {.acyclic.} = object
Rope* {.acyclic.} = ref object
## A rope data type. The empty rope is represented by `nil`.
left, right: Rope
length: int
data: string # not empty if a leaf
Expand All @@ -45,8 +45,7 @@ type

proc len*(a: Rope): int {.rtl, extern: "nro$1".} =
## The rope's length.
if a == nil: result = 0
else: result = a.length
if a == nil: 0 else: a.length

proc newRope(): Rope = new(result)
proc newRope(data: string): Rope =
Expand Down Expand Up @@ -128,8 +127,9 @@ proc insertInCache(s: string, tree: Rope): Rope =
proc rope*(s: string = ""): Rope {.rtl, extern: "nro$1Str".} =
## Converts a string to a rope.
runnableExamples:
var r = rope("I'm a rope")
let r = rope("I'm a rope")
doAssert $r == "I'm a rope"

if s.len == 0:
result = nil
else:
Expand All @@ -146,15 +146,17 @@ proc rope*(s: string = ""): Rope {.rtl, extern: "nro$1Str".} =
proc rope*(i: BiggestInt): Rope {.rtl, extern: "nro$1BiggestInt".} =
## Converts an int to a rope.
runnableExamples:
var r = rope(429)
let r = rope(429)
doAssert $r == "429"

result = rope($i)

proc rope*(f: BiggestFloat): Rope {.rtl, extern: "nro$1BiggestFloat".} =
## Converts a float to a rope.
runnableExamples:
var r = rope(4.29)
let r = rope(4.29)
doAssert $r == "4.29"

result = rope($f)

proc enableCache*() {.rtl, extern: "nro$1".} =
Expand All @@ -170,12 +172,9 @@ proc disableCache*() {.rtl, extern: "nro$1".} =
proc `&`*(a, b: Rope): Rope {.rtl, extern: "nroConcRopeRope".} =
## The concatenation operator for ropes.
runnableExamples:
var
r1 = rope("Hello, ")
r2 = rope("Nim!")

let r = r1 & r2
let r = rope("Hello, ") & rope("Nim!")
doAssert $r == "Hello, Nim!"

if a == nil:
result = b
elif b == nil:
Expand All @@ -189,78 +188,62 @@ proc `&`*(a, b: Rope): Rope {.rtl, extern: "nroConcRopeRope".} =
proc `&`*(a: Rope, b: string): Rope {.rtl, extern: "nroConcRopeStr".} =
## The concatenation operator for ropes.
runnableExamples:
var
r1 = rope("Hello, ")
r2 = "Nim!"

let r = r1 & r2
let r = rope("Hello, ") & "Nim!"
doAssert $r == "Hello, Nim!"

result = a & rope(b)

proc `&`*(a: string, b: Rope): Rope {.rtl, extern: "nroConcStrRope".} =
## The concatenation operator for ropes.
runnableExamples:
var
r1 = "Hello, "
r2 = rope("Nim!")

let r = r1 & r2
let r = "Hello, " & rope("Nim!")
doAssert $r == "Hello, Nim!"

result = rope(a) & b

proc `&`*(a: openArray[Rope]): Rope {.rtl, extern: "nroConcOpenArray".} =
## The concatenation operator for an openarray of ropes.
## The concatenation operator for an `openArray` of ropes.
runnableExamples:
let s = @[rope("Hello, "), rope("Nim"), rope("!")]
let r = &s
let r = &[rope("Hello, "), rope("Nim"), rope("!")]
doAssert $r == "Hello, Nim!"

for item in a: result = result & item

proc add*(a: var Rope, b: Rope) {.rtl, extern: "nro$1Rope".} =
## Adds `b` to the rope `a`.
runnableExamples:
var
r1 = rope("Hello, ")
r2 = rope("Nim!")
var r = rope("Hello, ")
r.add(rope("Nim!"))
doAssert $r == "Hello, Nim!"

r1.add(r2)
doAssert $r1 == "Hello, Nim!"
a = a & b

proc add*(a: var Rope, b: string) {.rtl, extern: "nro$1Str".} =
## Adds `b` to the rope `a`.
runnableExamples:
var
r1 = rope("Hello, ")
r2 = "Nim!"
var r = rope("Hello, ")
r.add("Nim!")
doAssert $r == "Hello, Nim!"

r1.add(r2)
doAssert $r1 == "Hello, Nim!"
a = a & b

proc `[]`*(r: Rope, i: int): char {.rtl, extern: "nroCharAt".} =
## Returns the character at position `i` in the rope `r`. This is quite
## expensive! Worst-case: O(n). If `i >= r.len`, `\0` is returned.
## expensive! Worst-case: O(n). If `i >= r.len or i < 0`, `\0` is returned.
runnableExamples:
let r1 = rope("Hello, Nim!")

doAssert r1[0] == 'H'
doAssert r1[7] == 'N'
doAssert r1[22] == '\0'
let r = rope("Hello, Nim!")

let r2 = rope("Hello") & rope(", Nim!")

doAssert r2[0] == 'H'
doAssert r2[7] == 'N'
doAssert r2[22] == '\0'
doAssert r[0] == 'H'
doAssert r[7] == 'N'
doAssert r[22] == '\0'

var x = r
var j = i
if x == nil: return
if x == nil or i < 0 or i >= r.len: return
while true:
if x != nil and x.data.len > 0:
if j < x.data.len: return x.data[j]
return '\0'
# leaf
return x.data[j]
else:
if x.left.length > j:
x = x.left
Expand All @@ -276,7 +259,7 @@ iterator leaves*(r: Rope): string =
var index = 0
for leave in r.leaves:
doAssert leave == s[index]
inc index
inc(index)

if r != nil:
var stack = @[r]
Expand Down Expand Up @@ -307,8 +290,7 @@ proc `$`*(r: Rope): string {.rtl, extern: "nroToString".} =
result = newStringOfCap(r.len)
for s in leaves(r): add(result, s)

proc `%`*(frmt: string, args: openArray[Rope]): Rope {.
rtl, extern: "nroFormat".} =
proc `%`*(frmt: string, args: openArray[Rope]): Rope {.rtl, extern: "nroFormat".} =
## `%` substitution operator for ropes. Does not support the `$identifier`
## nor `${identifier}` notations.
runnableExamples:
Expand All @@ -317,6 +299,10 @@ proc `%`*(frmt: string, args: openArray[Rope]): Rope {.

let r2 = "$# $# $#" % [rope("Nim"), rope("is"), rope("a great language")]
doAssert $r2 == "Nim is a great language"

let r3 = "${1} ${2} ${3}" % [rope("Nim"), rope("is"), rope("a great language")]
doAssert $r3 == "Nim is a great language"

var i = 0
var length = len(frmt)
result = nil
Expand Down Expand Up @@ -357,13 +343,13 @@ proc `%`*(frmt: string, args: openArray[Rope]): Rope {.
if i - 1 >= start:
add(result, substr(frmt, start, i - 1))

proc addf*(c: var Rope, frmt: string, args: openArray[Rope]) {.
rtl, extern: "nro$1".} =
proc addf*(c: var Rope, frmt: string, args: openArray[Rope]) {.rtl, extern: "nro$1".} =
## Shortcut for `add(c, frmt % args)`.
runnableExamples:
var r = rope("Dash: ")
r.addf "$1 $2 $3", [rope("Nim"), rope("is"), rope("a great language")]
doAssert $r == "Dash: Nim is a great language"

add(c, frmt % args)

when not defined(js) and not defined(nimscript):
Expand All @@ -386,14 +372,12 @@ when not defined(js) and not defined(nimscript):
bpos = 0
blen = readBuffer(f, addr(buf[0]), buf.len)
if blen == 0: # no more data in file
result = false
return
return false
let n = min(blen - bpos, slen - spos)
# TODO There's gotta be a better way of comparing here...
# TODO: There's gotta be a better way of comparing here...
if not equalMem(addr(buf[bpos]),
cast[pointer](cast[int](cstring(s))+spos), n):
result = false
return
cast[pointer](cast[int](cstring(s)) + spos), n):
return false
spos += n
bpos += n

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