make the docs of arithmetics better (#16510)

* fix

* Update lib/system/arithmetics.nim

Co-authored-by: Timothee Cour <timothee.cour2@gmail.com>

* Apply suggestions from code review

Co-authored-by: Timothee Cour <timothee.cour2@gmail.com>

* Apply suggestions from code review

Co-authored-by: Timothee Cour <timothee.cour2@gmail.com>

Co-authored-by: Timothee Cour <timothee.cour2@gmail.com>

1 files changed, 107 insertions, 126 deletions

diff --git a/lib/system/arithmetics.nim b/lib/system/arithmetics.nim
index f6c1b69ff..4242cd1e3 100644
--- a/lib/system/arithmetics.nim
+++ b/lib/system/arithmetics.nim
@@ -1,48 +1,44 @@
-proc succ*[T: Ordinal](x: T, y = 1): T {.magic: "Succ", noSideEffect.}
-  ## Returns the ``y``-th successor (default: 1) of the value ``x``.
-  ## ``T`` has to be an `ordinal type <#Ordinal>`_.
+proc succ*[T: Ordinal](x: T, y = 1): T {.magic: "Succ", noSideEffect.} =
+  ## Returns the `y`-th successor (default: 1) of the value `x`.
   ##
-  ## If such a value does not exist, ``OverflowDefect`` is raised
+  ## If such a value does not exist, `OverflowDefect` is raised
   ## or a compile time error occurs.
-  ##
-  ## .. code-block:: Nim
-  ##   let x = 5
-  ##   echo succ(5)    # => 6
-  ##   echo succ(5, 3) # => 8
-
-proc pred*[T: Ordinal](x: T, y = 1): T {.magic: "Pred", noSideEffect.}
-  ## Returns the ``y``-th predecessor (default: 1) of the value ``x``.
-  ## ``T`` has to be an `ordinal type <#Ordinal>`_.
-  ##
-  ## If such a value does not exist, ``OverflowDefect`` is raised
-  ## or a compile time error occurs.
-  ##
-  ## .. code-block:: Nim
-  ##   let x = 5
-  ##   echo pred(5)    # => 4
-  ##   echo pred(5, 3) # => 2
+  runnableExamples:
+    assert succ(5) == 6
+    assert succ(5, 3) == 8
 
-proc inc*[T: Ordinal](x: var T, y = 1) {.magic: "Inc", noSideEffect.}
-  ## Increments the ordinal ``x`` by ``y``.
-  ##
-  ## If such a value does not exist, ``OverflowDefect`` is raised or a compile
-  ## time error occurs. This is a short notation for: ``x = succ(x, y)``.
+proc pred*[T: Ordinal](x: T, y = 1): T {.magic: "Pred", noSideEffect.} =
+  ## Returns the `y`-th predecessor (default: 1) of the value `x`.
   ##
-  ## .. code-block:: Nim
-  ##  var i = 2
-  ##  inc(i)    # i <- 3
-  ##  inc(i, 3) # i <- 6
+  ## If such a value does not exist, `OverflowDefect` is raised
+  ## or a compile time error occurs.
+  runnableExamples:
+    assert pred(5) == 4
+    assert pred(5, 3) == 2
 
-proc dec*[T: Ordinal](x: var T, y = 1) {.magic: "Dec", noSideEffect.}
-  ## Decrements the ordinal ``x`` by ``y``.
+proc inc*[T: Ordinal](x: var T, y = 1) {.magic: "Inc", noSideEffect.} =
+  ## Increments the ordinal `x` by `y`.
   ##
-  ## If such a value does not exist, ``OverflowDefect`` is raised or a compile
-  ## time error occurs. This is a short notation for: ``x = pred(x, y)``.
+  ## If such a value does not exist, `OverflowDefect` is raised or a compile
+  ## time error occurs. This is a short notation for: `x = succ(x, y)`.
+  runnableExamples:
+    var i = 2
+    inc(i)
+    assert i == 3
+    inc(i, 3)
+    assert i == 6
+
+proc dec*[T: Ordinal](x: var T, y = 1) {.magic: "Dec", noSideEffect.} =
+  ## Decrements the ordinal `x` by `y`.
   ##
-  ## .. code-block:: Nim
-  ##  var i = 2
-  ##  dec(i)    # i <- 1
-  ##  dec(i, 3) # i <- -2
+  ## If such a value does not exist, `OverflowDefect` is raised or a compile
+  ## time error occurs. This is a short notation for: `x = pred(x, y)`.
+  runnableExamples:
+    var i = 2
+    dec(i)
+    assert i == 1
+    dec(i, 3)
+    assert i == -2
 
 
 
@@ -51,38 +47,38 @@ proc dec*[T: Ordinal](x: var T, y = 1) {.magic: "Dec", noSideEffect.}
 
 when defined(nimNoZeroExtendMagic):
   proc ze*(x: int8): int {.deprecated.} =
-    ## zero extends a smaller integer type to ``int``. This treats `x` as
+    ## zero extends a smaller integer type to `int`. This treats `x` as
     ## unsigned.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
     cast[int](uint(cast[uint8](x)))
 
   proc ze*(x: int16): int {.deprecated.} =
-    ## zero extends a smaller integer type to ``int``. This treats `x` as
+    ## zero extends a smaller integer type to `int`. This treats `x` as
     ## unsigned.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
     cast[int](uint(cast[uint16](x)))
 
   proc ze64*(x: int8): int64 {.deprecated.} =
-    ## zero extends a smaller integer type to ``int64``. This treats `x` as
+    ## zero extends a smaller integer type to `int64`. This treats `x` as
     ## unsigned.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
     cast[int64](uint64(cast[uint8](x)))
 
   proc ze64*(x: int16): int64 {.deprecated.} =
-    ## zero extends a smaller integer type to ``int64``. This treats `x` as
+    ## zero extends a smaller integer type to `int64`. This treats `x` as
     ## unsigned.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
     cast[int64](uint64(cast[uint16](x)))
 
   proc ze64*(x: int32): int64 {.deprecated.} =
-    ## zero extends a smaller integer type to ``int64``. This treats `x` as
+    ## zero extends a smaller integer type to `int64`. This treats `x` as
     ## unsigned.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
     cast[int64](uint64(cast[uint32](x)))
 
   proc ze64*(x: int): int64 {.deprecated.} =
-    ## zero extends a smaller integer type to ``int64``. This treats `x` as
-    ## unsigned. Does nothing if the size of an ``int`` is the same as ``int64``.
+    ## zero extends a smaller integer type to `int64`. This treats `x` as
+    ## unsigned. Does nothing if the size of an `int` is the same as `int64`.
     ## (This is the case on 64 bit processors.)
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
     cast[int64](uint64(cast[uint](x)))
@@ -94,46 +90,46 @@ when defined(nimNoZeroExtendMagic):
     cast[int8](x)
 
   proc toU16*(x: int): int16 {.deprecated.} =
-    ## treats `x` as unsigned and converts it to an ``int16`` by taking the last
+    ## treats `x` as unsigned and converts it to an `int16` by taking the last
     ## 16 bits from `x`.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
     cast[int16](x)
 
   proc toU32*(x: int64): int32 {.deprecated.} =
-    ## treats `x` as unsigned and converts it to an ``int32`` by taking the
+    ## treats `x` as unsigned and converts it to an `int32` by taking the
     ## last 32 bits from `x`.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
     cast[int32](x)
 
 elif not defined(js):
   proc ze*(x: int8): int {.magic: "Ze8ToI", noSideEffect, deprecated.}
-    ## zero extends a smaller integer type to ``int``. This treats `x` as
+    ## zero extends a smaller integer type to `int`. This treats `x` as
     ## unsigned.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
 
   proc ze*(x: int16): int {.magic: "Ze16ToI", noSideEffect, deprecated.}
-    ## zero extends a smaller integer type to ``int``. This treats `x` as
+    ## zero extends a smaller integer type to `int`. This treats `x` as
     ## unsigned.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
 
   proc ze64*(x: int8): int64 {.magic: "Ze8ToI64", noSideEffect, deprecated.}
-    ## zero extends a smaller integer type to ``int64``. This treats `x` as
+    ## zero extends a smaller integer type to `int64`. This treats `x` as
     ## unsigned.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
 
   proc ze64*(x: int16): int64 {.magic: "Ze16ToI64", noSideEffect, deprecated.}
-    ## zero extends a smaller integer type to ``int64``. This treats `x` as
+    ## zero extends a smaller integer type to `int64`. This treats `x` as
     ## unsigned.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
 
   proc ze64*(x: int32): int64 {.magic: "Ze32ToI64", noSideEffect, deprecated.}
-    ## zero extends a smaller integer type to ``int64``. This treats `x` as
+    ## zero extends a smaller integer type to `int64`. This treats `x` as
     ## unsigned.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
 
   proc ze64*(x: int): int64 {.magic: "ZeIToI64", noSideEffect, deprecated.}
-    ## zero extends a smaller integer type to ``int64``. This treats `x` as
-    ## unsigned. Does nothing if the size of an ``int`` is the same as ``int64``.
+    ## zero extends a smaller integer type to `int64`. This treats `x` as
+    ## unsigned. Does nothing if the size of an `int` is the same as `int64`.
     ## (This is the case on 64 bit processors.)
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
 
@@ -143,12 +139,12 @@ elif not defined(js):
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
 
   proc toU16*(x: int): int16 {.magic: "ToU16", noSideEffect, deprecated.}
-    ## treats `x` as unsigned and converts it to an ``int16`` by taking the last
+    ## treats `x` as unsigned and converts it to an `int16` by taking the last
     ## 16 bits from `x`.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
 
   proc toU32*(x: int64): int32 {.magic: "ToU32", noSideEffect, deprecated.}
-    ## treats `x` as unsigned and converts it to an ``int32`` by taking the
+    ## treats `x` as unsigned and converts it to an `int32` by taking the
     ## last 32 bits from `x`.
     ## **Deprecated since version 0.19.9**: Use unsigned integers instead.
 
@@ -167,20 +163,13 @@ proc `-`*(x: int16): int16 {.magic: "UnaryMinusI", noSideEffect.}
 proc `-`*(x: int32): int32 {.magic: "UnaryMinusI", noSideEffect.}
 proc `-`*(x: int64): int64 {.magic: "UnaryMinusI64", noSideEffect.}
 
-proc `not`*(x: int): int {.magic: "BitnotI", noSideEffect.}
+proc `not`*(x: int): int {.magic: "BitnotI", noSideEffect.} =
   ## Computes the `bitwise complement` of the integer `x`.
-  ##
-  ## .. code-block:: Nim
-  ##   var
-  ##     a = 0'u8
-  ##     b = 0'i8
-  ##     c = 1000'u16
-  ##     d = 1000'i16
-  ##
-  ##   echo not a # => 255
-  ##   echo not b # => -1
-  ##   echo not c # => 64535
-  ##   echo not d # => -1001
+  runnableExamples:
+    assert not 0'u8 == 255
+    assert not 0'i8 == -1
+    assert not 1000'u16 == 64535
+    assert not 1000'i16 == -1001
 proc `not`*(x: int8): int8 {.magic: "BitnotI", noSideEffect.}
 proc `not`*(x: int16): int16 {.magic: "BitnotI", noSideEffect.}
 proc `not`*(x: int32): int32 {.magic: "BitnotI", noSideEffect.}
@@ -207,34 +196,32 @@ proc `*`*(x, y: int16): int16 {.magic: "MulI", noSideEffect.}
 proc `*`*(x, y: int32): int32 {.magic: "MulI", noSideEffect.}
 proc `*`*(x, y: int64): int64 {.magic: "MulI", noSideEffect.}
 
-proc `div`*(x, y: int): int {.magic: "DivI", noSideEffect.}
+proc `div`*(x, y: int): int {.magic: "DivI", noSideEffect.} = 
   ## Computes the integer division.
   ##
-  ## This is roughly the same as ``trunc(x/y)``.
-  ##
-  ## .. code-block:: Nim
-  ##   ( 1 div  2) ==  0
-  ##   ( 2 div  2) ==  1
-  ##   ( 3 div  2) ==  1
-  ##   ( 7 div  3) ==  2
-  ##   (-7 div  3) == -2
-  ##   ( 7 div -3) == -2
-  ##   (-7 div -3) ==  2
+  ## This is roughly the same as `math.trunc(x/y).int`.
+  runnableExamples:
+    assert (1 div 2) == 0
+    assert (2 div 2) == 1
+    assert (3 div 2) == 1
+    assert (7 div 3) == 2
+    assert (-7 div 3) == -2
+    assert (7 div -3) == -2
+    assert (-7 div -3) == 2
 proc `div`*(x, y: int8): int8 {.magic: "DivI", noSideEffect.}
 proc `div`*(x, y: int16): int16 {.magic: "DivI", noSideEffect.}
 proc `div`*(x, y: int32): int32 {.magic: "DivI", noSideEffect.}
 proc `div`*(x, y: int64): int64 {.magic: "DivI", noSideEffect.}
 
-proc `mod`*(x, y: int): int {.magic: "ModI", noSideEffect.}
+proc `mod`*(x, y: int): int {.magic: "ModI", noSideEffect.} =
   ## Computes the integer modulo operation (remainder).
   ##
-  ## This is the same as ``x - (x div y) * y``.
-  ##
-  ## .. code-block:: Nim
-  ##   ( 7 mod  5) ==  2
-  ##   (-7 mod  5) == -2
-  ##   ( 7 mod -5) ==  2
-  ##   (-7 mod -5) == -2
+  ## This is the same as `x - (x div y) * y`.
+  runnableExamples:
+    assert (7 mod 5) == 2
+    assert (-7 mod 5) == -2
+    assert (7 mod -5) == 2
+    assert (-7 mod -5) == -2
 proc `mod`*(x, y: int8): int8 {.magic: "ModI", noSideEffect.}
 proc `mod`*(x, y: int16): int16 {.magic: "ModI", noSideEffect.}
 proc `mod`*(x, y: int32): int32 {.magic: "ModI", noSideEffect.}
@@ -248,7 +235,7 @@ when defined(nimOldShiftRight) or not defined(nimAshr):
   proc `shr`*(x: int32, y: SomeInteger): int32 {.magic: "ShrI", noSideEffect, deprecated: shrDepMessage.}
   proc `shr`*(x: int64, y: SomeInteger): int64 {.magic: "ShrI", noSideEffect, deprecated: shrDepMessage.}
 else:
-  proc `shr`*(x: int, y: SomeInteger): int {.magic: "AshrI", noSideEffect.}
+  proc `shr`*(x: int, y: SomeInteger): int {.magic: "AshrI", noSideEffect.} =
     ## Computes the `shift right` operation of `x` and `y`, filling
     ## vacant bit positions with the sign bit.
     ##
@@ -256,38 +243,36 @@ else:
     ## is different than in *C*.
     ##
     ## See also:
-    ## * `ashr proc <#ashr,int,SomeInteger>`_ for arithmetic shift right
-    ##
-    ## .. code-block:: Nim
-    ##   0b0001_0000'i8 shr 2 == 0b0000_0100'i8
-    ##   0b0000_0001'i8 shr 1 == 0b0000_0000'i8
-    ##   0b1000_0000'i8 shr 4 == 0b1111_1000'i8
-    ##   -1 shr 5 == -1
-    ##   1 shr 5 == 0
-    ##   16 shr 2 == 4
-    ##   -16 shr 2 == -4
+    ## * `ashr func<#ashr,int,SomeInteger>`_ for arithmetic shift right
+    runnableExamples:
+      assert 0b0001_0000'i8 shr 2 == 0b0000_0100'i8
+      assert 0b0000_0001'i8 shr 1 == 0b0000_0000'i8
+      assert 0b1000_0000'i8 shr 4 == 0b1111_1000'i8
+      assert -1 shr 5 == -1
+      assert 1 shr 5 == 0
+      assert 16 shr 2 == 4
+      assert -16 shr 2 == -4
   proc `shr`*(x: int8, y: SomeInteger): int8 {.magic: "AshrI", noSideEffect.}
   proc `shr`*(x: int16, y: SomeInteger): int16 {.magic: "AshrI", noSideEffect.}
   proc `shr`*(x: int32, y: SomeInteger): int32 {.magic: "AshrI", noSideEffect.}
   proc `shr`*(x: int64, y: SomeInteger): int64 {.magic: "AshrI", noSideEffect.}
 
 
-proc `shl`*(x: int, y: SomeInteger): int {.magic: "ShlI", noSideEffect.}
+proc `shl`*(x: int, y: SomeInteger): int {.magic: "ShlI", noSideEffect.} =
   ## Computes the `shift left` operation of `x` and `y`.
   ##
   ## **Note**: `Operator precedence <manual.html#syntax-precedence>`_
   ## is different than in *C*.
-  ##
-  ## .. code-block:: Nim
-  ##  1'i32 shl 4 == 0x0000_0010
-  ##  1'i64 shl 4 == 0x0000_0000_0000_0010
+  runnableExamples:
+    assert 1'i32 shl 4 == 0x0000_0010
+    assert 1'i64 shl 4 == 0x0000_0000_0000_0010
 proc `shl`*(x: int8, y: SomeInteger): int8 {.magic: "ShlI", noSideEffect.}
 proc `shl`*(x: int16, y: SomeInteger): int16 {.magic: "ShlI", noSideEffect.}
 proc `shl`*(x: int32, y: SomeInteger): int32 {.magic: "ShlI", noSideEffect.}
 proc `shl`*(x: int64, y: SomeInteger): int64 {.magic: "ShlI", noSideEffect.}
 
 when defined(nimAshr):
-  proc ashr*(x: int, y: SomeInteger): int {.magic: "AshrI", noSideEffect.}
+  proc ashr*(x: int, y: SomeInteger): int {.magic: "AshrI", noSideEffect.} =
     ## Shifts right by pushing copies of the leftmost bit in from the left,
     ## and let the rightmost bits fall off.
     ##
@@ -295,12 +280,11 @@ when defined(nimAshr):
     ## call syntax for it.
     ##
     ## See also:
-    ## * `shr proc <#shr,int,SomeInteger>`_
-    ##
-    ## .. code-block:: Nim
-    ##   ashr(0b0001_0000'i8, 2) == 0b0000_0100'i8
-    ##   ashr(0b1000_0000'i8, 8) == 0b1111_1111'i8
-    ##   ashr(0b1000_0000'i8, 1) == 0b1100_0000'i8
+    ## * `shr func<#shr,int,SomeInteger>`_
+    runnableExamples:
+      assert ashr(0b0001_0000'i8, 2) == 0b0000_0100'i8
+      assert ashr(0b1000_0000'i8, 8) == 0b1111_1111'i8
+      assert ashr(0b1000_0000'i8, 1) == 0b1100_0000'i8
   proc ashr*(x: int8, y: SomeInteger): int8 {.magic: "AshrI", noSideEffect.}
   proc ashr*(x: int16, y: SomeInteger): int16 {.magic: "AshrI", noSideEffect.}
   proc ashr*(x: int32, y: SomeInteger): int32 {.magic: "AshrI", noSideEffect.}
@@ -309,34 +293,31 @@ else:
   # used for bootstrapping the compiler
   proc ashr*[T](x: T, y: SomeInteger): T = discard
 
-proc `and`*(x, y: int): int {.magic: "BitandI", noSideEffect.}
+proc `and`*(x, y: int): int {.magic: "BitandI", noSideEffect.} =
   ## Computes the `bitwise and` of numbers `x` and `y`.
-  ##
-  ## .. code-block:: Nim
-  ##   (0b0011 and 0b0101) == 0b0001
-  ##   (0b0111 and 0b1100) == 0b0100
+  runnableExamples:
+    assert (0b0011 and 0b0101) == 0b0001
+    assert (0b0111 and 0b1100) == 0b0100
 proc `and`*(x, y: int8): int8 {.magic: "BitandI", noSideEffect.}
 proc `and`*(x, y: int16): int16 {.magic: "BitandI", noSideEffect.}
 proc `and`*(x, y: int32): int32 {.magic: "BitandI", noSideEffect.}
 proc `and`*(x, y: int64): int64 {.magic: "BitandI", noSideEffect.}
 
-proc `or`*(x, y: int): int {.magic: "BitorI", noSideEffect.}
+proc `or`*(x, y: int): int {.magic: "BitorI", noSideEffect.} =
   ## Computes the `bitwise or` of numbers `x` and `y`.
-  ##
-  ## .. code-block:: Nim
-  ##   (0b0011 or 0b0101) == 0b0111
-  ##   (0b0111 or 0b1100) == 0b1111
+  runnableExamples:
+    assert (0b0011 or 0b0101) == 0b0111
+    assert (0b0111 or 0b1100) == 0b1111
 proc `or`*(x, y: int8): int8 {.magic: "BitorI", noSideEffect.}
 proc `or`*(x, y: int16): int16 {.magic: "BitorI", noSideEffect.}
 proc `or`*(x, y: int32): int32 {.magic: "BitorI", noSideEffect.}
 proc `or`*(x, y: int64): int64 {.magic: "BitorI", noSideEffect.}
 
-proc `xor`*(x, y: int): int {.magic: "BitxorI", noSideEffect.}
+proc `xor`*(x, y: int): int {.magic: "BitxorI", noSideEffect.} =
   ## Computes the `bitwise xor` of numbers `x` and `y`.
-  ##
-  ## .. code-block:: Nim
-  ##   (0b0011 xor 0b0101) == 0b0110
-  ##   (0b0111 xor 0b1100) == 0b1011
+  runnableExamples:
+    assert (0b0011 xor 0b0101) == 0b0110
+    assert (0b0111 xor 0b1100) == 0b1011
 proc `xor`*(x, y: int8): int8 {.magic: "BitxorI", noSideEffect.}
 proc `xor`*(x, y: int16): int16 {.magic: "BitxorI", noSideEffect.}
 proc `xor`*(x, y: int32): int32 {.magic: "BitxorI", noSideEffect.}