SixtyPical/tests/SixtyPical Fallthru.md

SixtyPical Fallthru

This is a test suite, written in Falderal format, for SixtyPical's ability to detect which routines make tail calls to other routines, and thus can be re-arranged to simply "fall through" to them.

-> Functionality "Dump fallthru map of SixtyPical program" is implemented by
-> shell command "bin/sixtypical --analyze-only --dump-fallthru-map --traceback %(test-body-file)"

-> Tests for functionality "Dump fallthru map of SixtyPical program"

A single routine, obviously, falls through to nothing and has nothing fall through to it.

| define main routine
| {
| }
= {}

If main does a goto foo, then it can fall through to foo.

| define foo routine trashes a, z, n
| {
|     ld a, 0
| }
| 
| define main routine trashes a, z, n
| {
|     goto foo
| }
= {
=     "foo": [
=         "main"
=     ]
= }

More than one routine can fall through to a routine.

If main does a goto foo, then it can fall through to foo.

| define foo routine trashes a, z, n
| {
|     ld a, 0
| }
| 
| define bar routine trashes a, z, n
| {
|     ld a, 0
|     goto foo
| }
| 
| define main routine trashes a, z, n
| {
|     goto foo
| }
= {
=     "foo": [
=         "bar", 
=         "main"
=     ]
= }

There is nothing stopping two routines from tail-calling each other, but we will only be able to make one of them, at most, fall through to the other.

| define foo routine trashes a, z, n
| {
|     ld a, 0
|     goto bar
| }
| 
| define bar routine trashes a, z, n
| {
|     ld a, 0
|     goto foo
| }
| 
| define main routine trashes a, z, n
| {
| }
= {
=     "bar": [
=         "foo"
=     ], 
=     "foo": [
=         "bar"
=     ]
= }

If a routine does two tail calls (which is possible because they can be in different branches of an if) it cannot fall through to another routine.

| define foo routine trashes a, z, n
| {
|     ld a, 0
| }
| 
| define bar routine trashes a, z, n
| {
|     ld a, 0
| }
| 
| define main routine inputs z trashes a, z, n
| {
|     if z {
|         goto foo
|     } else {
|         goto bar
|     }
| }
= {}

Similarly, a tail call to a vector can't be turned into a fallthru, because we don't necessarily know what actual routine the vector contains.

| vector routine trashes a, z, n
|   vec
| 
| define foo routine trashes a, z, n
| {
|     ld a, 0
| }
| 
| define bar routine trashes a, z, n
| {
|     ld a, 0
| }
| 
| define main routine outputs vec trashes a, z, n
| {
|     copy bar, vec
|     goto vec
| }
= {}