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Shell: Add runtime errors and implement break/continue

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Such errors are raised when SyntaxError nodes are executed, and are also
used for internal control flow.
The 'break' and 'continue' commands are currently only allowed inside
for loops, and outside function bodies.

This also adds a 'loop' keyword for infinite loops.
This commit is contained in:
AnotherTest 2020-12-10 18:25:13 +03:30 • committed by Andreas Kling
parent 9bd81f34a5
commit 5e5eb615ec
14 changed files with 384 additions and 62 deletions
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41
Base/usr/share/man/man5/Shell.md
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@ -221,6 +221,28 @@ $ for * { mv $it 1-$it }
$ for i in $(seq 1 100) { echo $i >> foo }
```
##### Infinite Loops
Infinite loops (as denoted by the keyword `loop`) can be used to repeat a block until the block runs `break`, or the loop terminates by external sources (interrupts, program exit, and terminating signals).
The behaviour regarding SIGINT and other signals is the same as for loops (mentioned above).
###### Examples
```sh
# Keep deleting a file
loop {
rm -f foo
}
```
###### Examples
```sh
# Iterate over every non-hidden file in the current directory, and prepend '1-' to its name.
$ for * { mv $it 1-$it }
# Iterate over a sequence and write each element to a file
$ for i in $(seq 1 100) { echo $i >> foo }
```
##### Subshells
Subshells evaluate a given block in a new instance (fork) of the current shell process. to create a subshell, any valid shell code can be enclosed in braces.
@ -299,7 +321,7 @@ sequence :: variable_decls? or_logical_sequence terminator sequence
| variable_decls? function_decl (terminator sequence)?
| variable_decls? terminator sequence
function_decl :: identifier '(' (ws* identifier)* ')' ws* '{' toplevel '}'
function_decl :: identifier '(' (ws* identifier)* ')' ws* '{' [!c] toplevel '}'
or_logical_sequence :: and_logical_sequence '|' '|' and_logical_sequence
| and_logical_sequence
@ -318,12 +340,19 @@ pipe_sequence :: command '|' pipe_sequence
| control_structure '|' pipe_sequence
| control_structure
control_structure :: for_expr
| if_expr
| subshell
| match_expr
control_structure[c] :: for_expr
| loop_expr
| if_expr
| subshell
| match_expr
| ?c: continuation_control
for_expr :: 'for' ws+ (identifier ' '+ 'in' ws*)? expression ws+ '{' toplevel '}'
continuation_control :: 'break'
| 'continue'
for_expr :: 'for' ws+ (identifier ' '+ 'in' ws*)? expression ws+ '{' [c] toplevel '}'
loop_expr :: 'loop' ws* '{' [c] toplevel '}'
if_expr :: 'if' ws+ or_logical_sequence ws+ '{' toplevel '}' else_clause?