From abbf34e53f88fc38233e4377611b71646f5ca3c9 Mon Sep 17 00:00:00 2001
From: Takafumi Arakaki <aka.tkf@gmail.com>
Date: Sun, 24 Apr 2022 01:02:27 -0700
Subject: [PATCH] Add `Try.map` (#48)

---
 docs/src/index.md               |  1 +
 src/Try.jl                      |  3 +++
 src/docs/map.md                 | 25 +++++++++++++++++++++++++
 src/tools.jl                    | 23 +++++++++++++++++++++++
 test/TryTests/src/test_tools.jl |  7 +++++++
 5 files changed, 59 insertions(+)
 create mode 100644 src/docs/map.md
 create mode 100644 src/tools.jl

diff --git a/docs/src/index.md b/docs/src/index.md
index 1722019..6152542 100644
--- a/docs/src/index.md
+++ b/docs/src/index.md
@@ -15,6 +15,7 @@ Try.unwrap
 Try.unwrap_err
 Try.oktype
 Try.errtype
+Try.map
 ```
 
 ## Short-circuit evaluation
diff --git a/src/Try.jl b/src/Try.jl
index b80f480..875db05 100644
--- a/src/Try.jl
+++ b/src/Try.jl
@@ -34,6 +34,8 @@ struct IsOkError <: InternalPrelude.Exception
     InternalPrelude._IsOkError(ok) = new(ok)
 end
 
+function map end
+
 macro and_return end
 function var"@?" end
 function var"@return" end
@@ -57,6 +59,7 @@ using .ExternalDocstrings: @define_docstrings
 
 include("core.jl")
 include("errortrace.jl")
+include("tools.jl")
 include("branch.jl")
 include("show.jl")
 
diff --git a/src/docs/map.md b/src/docs/map.md
new file mode 100644
index 0000000..3efdc74
--- /dev/null
+++ b/src/docs/map.md
@@ -0,0 +1,25 @@
+    Try.map(f, result) -> result′
+    Try.map(f, Ok(value)) -> Ok(f(value))
+    Try.map(_, err::Err) -> err
+    Try.map(f, Some(value)) -> Some(f(value))
+    Try.map(_, nothing) -> nothing
+    Try.map(f) -> result -> Try.map(f, result)
+
+Apply `f` in the value wrapped in the "successful" result.
+
+# Examples
+
+```julia
+julia> using Try
+
+julia> Try.map(x -> x + 1, Ok(1))
+Try.Ok: 2
+
+julia> Try.map(x -> x + 1, Err(KeyError(:a)))
+Try.Err: KeyError: key :a not found
+
+julia> Try.map(x -> x + 1, Some(1))
+Some(2)
+
+julia> Try.map(x -> x + 1, nothing)
+```
diff --git a/src/tools.jl b/src/tools.jl
new file mode 100644
index 0000000..b5a86ca
--- /dev/null
+++ b/src/tools.jl
@@ -0,0 +1,23 @@
+Try.map(f, ok::Ok) = Ok(f(ok.value))
+Try.map(_, err::Err) = err
+
+function Try.map(f, result)
+    if Try.isok(result)
+        Ok(f(Try.unwrap(result)))
+    else
+        # Need to "forget" about any Ok value type information:
+        Err(Try.unwrap_err(result))
+    end
+end
+
+Try.map(f, some::Some) = Some(f(something(some)))
+Try.map(_, ::Nothing) = nothing
+
+struct TryMap{F} <: Function
+    f::F
+end
+TryMap(::Type{T}) where {T} = TryMap{Type{T}}(T)
+
+(f::TryMap)(x) = Try.map(f.f, x)
+
+Try.map(f::F) where {F} = TryMap(f)
diff --git a/test/TryTests/src/test_tools.jl b/test/TryTests/src/test_tools.jl
index a0573c1..dcf1989 100644
--- a/test/TryTests/src/test_tools.jl
+++ b/test/TryTests/src/test_tools.jl
@@ -144,4 +144,11 @@ function test_macro()
     @test demo_macro(1:0) === :oob
 end
 
+function test_map()
+    @test Try.map(x -> x + 1, Ok(1)) == Try.Ok(2)
+    @test Try.map(x -> x + 1, Err(KeyError(:a))) == Err(KeyError(:a))
+    @test Try.map(x -> x + 1, Some(1)) == Some(2)
+    @test Try.map(x -> x + 1, nothing) === nothing
+end
+
 end  # module