From 850fef98529ffee6908a9f46f0a06e02861afa4b Mon Sep 17 00:00:00 2001
From: Ayke van Laethem <aykevanlaethem@gmail.com>
Date: Thu, 19 Apr 2018 20:23:48 +0200
Subject: [PATCH] Add builtin len(string)

---
 src/examples/hello/hello.go |  5 +++++
 tgo.go                      | 19 ++++++++++++++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/src/examples/hello/hello.go b/src/examples/hello/hello.go
index f5d35cc5..ea6d14ac 100644
--- a/src/examples/hello/hello.go
+++ b/src/examples/hello/hello.go
@@ -18,11 +18,16 @@ func main() {
 	println("3 + 12 =", add(3, 12))
 	println("fib(11) =", fib(11))
 	println("sumrange(100) =", sumrange(100))
+	println("strlen foo:", strlen("foo"))
 
 	thing := Thing{"foo"}
 	println("thing:", thing.String())
 }
 
+func strlen(s string) int {
+	return len(s)
+}
+
 func calculateAnswer() int {
 	seven := 7
 	return SIX * seven
diff --git a/tgo.go b/tgo.go
index 223f58aa..ab14d9e6 100644
--- a/tgo.go
+++ b/tgo.go
@@ -76,7 +76,7 @@ func NewCompiler(pkgName, triple string) (*Compiler, error) {
 	c.intType = llvm.Int32Type()
 	c.stringLenType = llvm.Int32Type()
 
-	// Length-prefixed string.
+	// Go string: tuple of (len, ptr)
 	c.stringType = llvm.StructType([]llvm.Type{c.stringLenType, llvm.PointerType(llvm.Int8Type(), 0)}, false)
 
 	printstringType := llvm.FunctionType(llvm.VoidType(), []llvm.Type{c.stringType}, false)
@@ -427,6 +427,23 @@ func (c *Compiler) parseBuiltin(frame *Frame, instr *ssa.CallCommon, call *ssa.B
 			c.builder.CreateCall(c.printnlFunc, nil, "")
 		}
 		return llvm.Value{}, nil // print() or println() returns void
+	case "len":
+		arg := instr.Args[0]
+		value, err := c.parseExpr(frame, arg)
+		if err != nil {
+			return llvm.Value{}, err
+		}
+		switch typ := arg.Type().(type) {
+		case *types.Basic:
+			switch typ.Kind() {
+			case types.String:
+				return c.builder.CreateExtractValue(value, 0, "len"), nil
+			default:
+				return llvm.Value{}, errors.New("todo: len: unknown basic type")
+			}
+		default:
+			return llvm.Value{}, errors.New("todo: len: unknown type")
+		}
 	default:
 		return llvm.Value{}, errors.New("todo: builtin: " + name)
 	}