Currying, Combinators, and organization

1 files changed, 28 insertions, 0 deletions

diff --git a/src/compose.zig b/src/compose.zig
new file mode 100644
index 0000000..61ebb20
--- /dev/null
+++ b/src/compose.zig
@@ -0,0 +1,28 @@
+const std = @import("std");
+const typeVerify = @import("util.zig").typeVerify;
+
+/// ```zig
+/// (fn (fn (b) c, fn (a) b) fn (a) c)
+/// ```
+/// Function composition
+/// Type signature: (a -> b) -> (b -> c) -> (a -> c)
+/// `outerFunc` and `innerFunc` are functions of types `b -> c` and `a -> b` respectively
+/// Haskell equivalent: `outerFunc . innerFunc`
+pub fn compose(
+    comptime outerFunc: anytype,
+    comptime innerFunc: anytype
+) blk:{
+    _=typeVerify(@TypeOf(outerFunc), .{ .@"fn" });
+    _=typeVerify(@TypeOf(innerFunc), .{ .@"fn" });
+    const out = @typeInfo(@TypeOf(outerFunc)).@"fn".return_type.?;
+    const in = @typeInfo(@TypeOf(innerFunc)).@"fn".params[0].type.?;
+    break :blk fn(in) out;
+} {
+    const out = @typeInfo(@TypeOf(outerFunc)).@"fn".return_type.?;
+    const in = @typeInfo(@TypeOf(innerFunc)).@"fn".params[0].type.?;
+    return struct {
+        fn func(input: in) out {
+            return outerFunc(innerFunc(input));
+        }
+    }.func;
+}