Add helper function to print numbers as ordinal numerals (#1405)

src/AbstractAlgebra.jl

@@ -261,6 +261,7 @@ export NotImplementedError
 export NotInvertibleError
 export NumField
 export NumFieldElem
+export ordinal_number_string
 export parent_type
 export pluralize
 export PolyRing
@@ -292,7 +293,7 @@ export ZZ
 
 include("Attributes.jl")
 include("AliasMacro.jl")
-include("Pluralize.jl")
+include("PrintHelper.jl")
 
 # alternative names for some functions from Base
 export is_empty, is_even, is_equal, is_finite, is_inf, is_integer, is_less, is_odd, is_one, is_real, is_subset, is_valid, is_zero

src/Pluralize.jl → src/PrintHelper.jl

@@ -109,3 +109,40 @@ function Base.show(io::IO, quantity::ItemQuantity)
         print(io, pluralize(quantity.noun))
     end
 end
+
+"""
+    ordinal_number_string(number::Int)
+
+A helper function which returns `number` as a string in ordinal form.
+
+# Examples
+```julia
+julia> ordinal_number_string(1)
+"1st"
+
+julia> ordinal_number_string(2)
+"2nd"
+
+julia> ordinal_number_string(3)
+"3rd"
+
+julia> ordinal_number_string(4)
+"4rd"
+```
+"""
+function ordinal_number_string(number::Int)
+    number >= 0 || error("number must be non-negative")
+    mod100 = mod(number, 100)
+    mod10 = mod(number, 10)
+    if mod100 in 11:13
+        return "$(number)th"
+    elseif mod10 == 1
+        return "$(number)st"
+    elseif mod10 == 2
+        return "$(number)nd"
+    elseif mod10 == 3
+        return "$(number)rd"
+    else
+        return "$(number)th"
+    end
+end

test/AbstractAlgebra-test.jl

@@ -14,5 +14,5 @@ include("Maps-test.jl")
 include("Benchmark-test.jl")
 include("Factor-test.jl")
 include("PrettyPrinting-test.jl")
-include("Pluralize-test.jl")
+include("PrintHelper-test.jl")
 include("misc-test.jl")

test/PrintHelper-test.jl

@@ -0,0 +1,46 @@
+@testset "pluralize" begin
+  @test pluralize("basis") == "bases"
+  @test pluralize("child") == "children"
+  @test pluralize("generator") == "generators"
+  @test pluralize("indeterminate") == "indeterminates"
+  @test pluralize("matrix") == "matrices"
+  @test pluralize("maximum") == "maxima"
+  @test pluralize("polyhedron") == "polyhedra"
+  @test pluralize("tetrahedron") == "tetrahedra"
+  @test pluralize("variable") == "variables"
+  @test pluralize("variety") == "varieties"
+  @test pluralize("vertex") == "vertices"
+end
+
+@testset "ItemQuantity" begin
+  @test string(ItemQuantity(0, "generator")) == "0 generators"
+  @test string(ItemQuantity(1, "generator")) == "1 generator"
+  @test string(ItemQuantity(2, "generator")) == "2 generators"
+  @test string(ItemQuantity(0, "ox", "oxen")) == "0 oxen"
+  @test string(ItemQuantity(1, "ox", "oxen")) == "1 ox"
+  @test string(ItemQuantity(2, "ox", "oxen")) == "2 oxen"
+end
+
+@testset "ordinal_number_string" begin
+  @test ordinal_number_string(0) == "0th"
+  @test ordinal_number_string(1) == "1st"
+  @test ordinal_number_string(2) == "2nd"
+  @test ordinal_number_string(3) == "3rd"
+  @test ordinal_number_string(4) == "4th"
+  @test ordinal_number_string(5) == "5th"
+  @test ordinal_number_string(10) == "10th"
+  @test ordinal_number_string(11) == "11th"
+  @test ordinal_number_string(12) == "12th"
+  @test ordinal_number_string(13) == "13th"
+  @test ordinal_number_string(14) == "14th"
+  @test ordinal_number_string(20) == "20th"
+  @test ordinal_number_string(21) == "21st"
+  @test ordinal_number_string(22) == "22nd"
+  @test ordinal_number_string(23) == "23rd"
+  @test ordinal_number_string(24) == "24th"
+  @test ordinal_number_string(100) == "100th"
+  @test ordinal_number_string(101) == "101st"
+  @test ordinal_number_string(102) == "102nd"
+  @test ordinal_number_string(103) == "103rd"
+  @test ordinal_number_string(104) == "104th"
+end