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+# Thinks that tripped me up
+
+# Underscores
+
+Using _ for Lisp names.
+
+# typedef struct
+
+```C
+typedef struct
+{
+  size_t size;
+  size_t stride;
+  double * data;
+  gsl_block * block;
+  int owner;
+} gsl_vector;
+```
+
+prescheme generated this syntax for
+
+```lisp
+(define-wrapper-type gsl-vector)
+```
+
+```C
+struct gsl_vector {
+};
+
+struct gsl_vector *vector_3X;
+```
+
+resulting in
+
+```
+expected 'gsl_vector *' but argument is of type 'struct gsl_vector *'
+   82 | void gsl_vector_free (gsl_vector * v);
+```
+
+how to map one to the other? If you take out the struct it works. So, somehow, I need to create an opaque data structure.
+
+```
+(define (gsl-create-vector size) ; gsl_vector_alloc (3);
+  ((external "gsl_vector_alloc" (=> (integer) (^ unit)))
+   size))
+
+(define (gsl-destroy-vector vector)
+  ((external "gsl_vector_free" (=> (address) unit))
+   vector))
+```
+
+as unit translate to void that works - but there is no type safety. Well, at least not at the prescheme level.
+
+ps-compiler/prescheme/type.scm
+make-pointer-type
+
+For now I solved it by having sed edit out the 'struct' from the C code.
+
+# Floating point
+
+Initializing with 1.0 (leading zero) works. But 1.1 does not. The c-code becomes an empty space.
+
+```
+openblas.c:36:108: error: expected expression before ')' token
+   36 |     else {gsl_vector_set(vector_2X, 0, 0.0);gsl_vector_set(vector_2X, 1, 1.0);gsl_vector_set(vector_2X, 2, );gsl_vector_set(vector_2X, 3, 4.0);gsl_vector_set(vector_2X, 4, 5.0);
+```
+
+This was fixed by Andrew Whatson for me!
+
+# Loading a module
+
+Requires restarting prescheme? Note that file prescheme/memory.scm is loaded with ps-memory.
+
+```
+(define-structure openblas (export main)
+  (open prescheme)
+  ;; (open ps-receive)
+  (open ps-memory)
+  ;; (open prescheme interface)
+  (open ps-utils)
+  (open ps-string)
+  (open ps-vector)
+  ;; (open prescheme interfaces)
+  (files openblas))
+```
+
+# SIMDE
+
+Let's try to multiply a vector with a scalar.
+
+```
+const __m128 scalar = _mm_set1_ps(s);
+__m128 result = _mm_mul_ps(vector, scalar);
+```