task: variables in registers vs memory

tutorial/index.md

@@ -167,3 +167,28 @@ ask questions or share your experience](http://akkartik.name/contact).
 One gotcha to keep in mind is that numbers in Mu must always be in hexadecimal
 notation, starting with `0x`. Use a calculator on your computer or phone to
 convert 42 to hexadecimal, or [this page on your web browser](http://akkartik.github.io/mu/tutorial/converter.html).
+
+## Task 5: variables in registers, variables in memory
+
+We'll now practice managing one variable in a register (like last time) and
+a second one in memory. To prepare for this, reread the first section of the
+[Mu syntax description](https://github.com/akkartik/mu/blob/main/mu.md), and
+then its section on [local variables](https://github.com/akkartik/mu/blob/main/mu.md#local-variables).
+The section on [integer primitives](https://github.com/akkartik/mu/blob/main/mu.md#integer-primitives)
+also provides a useful cheatsheet of the instruction forms you will need.
+
+```
+fn foo -> _/eax: int {
+  var x: int
+  # statement 1: store 3 in x
+  # statement 2: define a new variable 'y' in register eax and store 4 in it
+  # statement 3: add y to x, storing the result in x
+  return x
+}
+```
+
+Again, you're encouraged to repeatedly try out your programs by running this
+command as often as you like:
+```
+./translate tutorial/task5.mu  &&  qemu-system-i386 code.img
+```

tutorial/task4.mu

@@ -8,7 +8,7 @@ fn the-answer -> _/eax: int {
 
 fn test-the-answer {
   var result/eax: int <- the-answer
-  check-ints-equal result, 0x2a, "F - the-answer should return 42, but didn't."
+  check-ints-equal result, 0x2a, "F - the-answer should return 42, but didn't"
 }
 
 fn main {

tutorial/task5-solution.mu

@@ -0,0 +1,18 @@
+fn foo -> _/eax: int {
+  var x: int
+  # statement 1: store 3 in x
+  copy-to x, 3
+  # statement 2: define a new variable 'y' in register eax and store 4 in it
+  var y/eax: int <- copy 4
+  # statement 3: add y to x, storing the result in x
+  add-to x, y
+  return x
+}
+
+fn test-foo {
+  var result/eax: int <- foo
+  check-ints-equal result, 7, "F - foo should return 7, but didn't"
+}
+
+fn main {
+}

tutorial/task5.mu

@@ -0,0 +1,15 @@
+fn foo -> _/eax: int {
+  var x: int
+  # statement 1: store 3 in x
+  # statement 2: define a new variable 'y' in register eax and store 4 in it
+  # statement 3: add y to x, storing the result in x
+  return x
+}
+
+fn test-foo {
+  var result/eax: int <- foo
+  check-ints-equal result, 7, "F - foo should return 7, but didn't"
+}
+
+fn main {
+}