Tweak how-to.md so that the extracted code builds

how-to.md

@@ -136,31 +136,36 @@ Alternatively, the allocated heap and stack size can be set in `basis_ffi.c`
 by modifying these lines in the file.
 Note that `cml_heap_sz` and `cml_stack_sz` are given in bytes here.
 
-    unsigned long sz = 1024*1024; // 1 MB unit
-    unsigned long cml_heap_sz = 1024 * sz;    // Default: 1 GB heap
-    unsigned long cml_stack_sz = 1024 * sz;   // Default: 1 GB stack
+```
+unsigned long sz = 1024*1024; // 1 MB unit
+unsigned long cml_heap_sz = 1024 * sz;    // Default: 1 GB heap
+unsigned long cml_stack_sz = 1024 * sz;   // Default: 1 GB stack
+```
 
 Basic profiling
 -------------------------------------
 
 On Linux systems, CakeML executables can be profiled using `perf`.
 As an example, we may profile the factorial program by running:
 
-    $ perf record ./fac.cake 30000
+```
+$ perf record ./fac.cake 30000
+```
 
 The report generated by `perf` shows that most of the time is spent in
 the bignum library (`LongDiv` is used internally there):
 
-    $ perf report
-
-    Samples: 20K of event 'cycles', Event count (approx.): 15828778212
-    Overhead  Command   Shared Object      Symbol
-      52.88%  fac.cake  fac.cake           [.] cml__LongDiv_21
-      16.19%  fac.cake  fac.cake           [.] cml__Bignum_50
-      12.10%  fac.cake  fac.cake           [.] cml__Bignum_47
-       6.31%  fac.cake  fac.cake           [.] cml__Replicate_9
-      ...
-
+```
+$ perf report
+
+Samples: 20K of event 'cycles', Event count (approx.): 15828778212
+Overhead  Command   Shared Object      Symbol
+  52.88%  fac.cake  fac.cake           [.] cml__LongDiv_21
+  16.19%  fac.cake  fac.cake           [.] cml__Bignum_50
+  12.10%  fac.cake  fac.cake           [.] cml__Bignum_47
+   6.31%  fac.cake  fac.cake           [.] cml__Replicate_9
+  ...
+```
 
 How CakeML differs from SML and OCaml
 -------------------------------------