From a399d5d1bf6d5e8ad0aa41d54211ddc3e5efef75 Mon Sep 17 00:00:00 2001
From: Klaus Alfert <klaus.alfert@gmail.com>
Date: Sat, 17 Apr 2021 17:51:47 +0200
Subject: [PATCH 1/2] example for using flatmap (as in #79)

---
 example_flatmap_test.go | 54 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)
 create mode 100644 example_flatmap_test.go

diff --git a/example_flatmap_test.go b/example_flatmap_test.go
new file mode 100644
index 0000000..e4ddc8c
--- /dev/null
+++ b/example_flatmap_test.go
@@ -0,0 +1,54 @@
+package gopter_test
+
+import (
+	"reflect"
+
+	"github.com/leanovate/gopter"
+	"github.com/leanovate/gopter/gen"
+	"github.com/leanovate/gopter/prop"
+)
+
+func Example_flatmap() {
+
+	type IntPair struct {
+		Fst int
+		Snd int
+	}
+
+	// Generate a pair of integers, such that the first
+	// is in the range of 10-20 and the second in the
+	// in the range of 2k-50, depending on the value of
+	// the first.
+	genIntPair := func() gopter.Gen {
+		return gen.IntRange(10, 20).FlatMap(func(v interface{}) gopter.Gen {
+			k := v.(int)
+			n := gen.Const(k)
+			m := gen.IntRange(2*k, 50)
+			var gen_map = map[string]gopter.Gen{"Fst": n, "Snd": m}
+			return gen.Struct(
+				reflect.TypeOf(IntPair{}),
+				gen_map,
+			)
+		},
+			reflect.TypeOf(int(0)))
+	}
+
+	parameters := gopter.DefaultTestParameters()
+	parameters.Rng.Seed(1234) // Just for this example to generate reproducible results
+	properties := gopter.NewProperties(parameters)
+
+	properties.Property("Generate a dependent pair of integers", prop.ForAll(
+		func(p IntPair) bool {
+			a := p.Fst
+			b := p.Snd
+			return a*2 <= b
+		},
+		genIntPair(),
+	))
+
+	// When using testing.T you might just use: properties.TestingRun(t)
+	properties.Run(gopter.ConsoleReporter(false))
+
+	// Output:
+	// + Generate a dependent pair of integers: OK, passed 100 tests.
+}

From daf756ed25105c1ce71643d7bfae49227df86075 Mon Sep 17 00:00:00 2001
From: Klaus Alfert <klaus.alfert@gmail.com>
Date: Sat, 17 Apr 2021 19:19:30 +0200
Subject: [PATCH 2/2] More concise version by using Map to construct the pair

---
 example_flatmap_test.go | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/example_flatmap_test.go b/example_flatmap_test.go
index e4ddc8c..037be87 100644
--- a/example_flatmap_test.go
+++ b/example_flatmap_test.go
@@ -22,13 +22,9 @@ func Example_flatmap() {
 	genIntPair := func() gopter.Gen {
 		return gen.IntRange(10, 20).FlatMap(func(v interface{}) gopter.Gen {
 			k := v.(int)
-			n := gen.Const(k)
-			m := gen.IntRange(2*k, 50)
-			var gen_map = map[string]gopter.Gen{"Fst": n, "Snd": m}
-			return gen.Struct(
-				reflect.TypeOf(IntPair{}),
-				gen_map,
-			)
+			return gen.IntRange(2*k, 50).Map(func(m int) IntPair {
+				return IntPair{Fst: k, Snd: m}
+			})
 		},
 			reflect.TypeOf(int(0)))
 	}