nomsu/lib/control_flow.nom

require "lib/metaprogramming.nom"
require "lib/operators.nom"
require "lib/utils.nom"

# Conditionals
compile [if %condition %if_body] to code: ".."
    |if \(%condition as lua) then;
    |    \(%if_body as lua statements)
    |end;

compile [if %condition %if_body else %else_body] to code: ".."
    |if \(%condition as lua) then;
    |    \(%if_body as lua statements)
    |else;
    |    \(%else_body as lua statements)
    |end;

# Return
compile [return] to code: "do; return; end;"
compile [return %return-value] to code: "do; return \(%return-value as lua); end;"

# GOTOs
compile [-> %label] to code: ".."
    |::label_\(nomsu "var_to_lua_identifier" [%label])::;
compile [go to %label] to code: ".."
    |goto label_\(nomsu "var_to_lua_identifier" [%label]);

# Loop control flow
compile [stop, stop loop, break] to code: "break"
compile [stop for, stop for-loop, break for] to code: "goto break_for"
compile [stop repeat, stop repeat-loop, break repeat] to code: "goto break_repeat"
compile [stop %var, break %var] to code: ".."
    |goto break_\(nomsu "var_to_lua_identifier" [%var]);

compile [continue, continue loop] to code: "continue"
compile [continue for, continue for-loop] to code: "goto continue_for"
compile [continue repeat, continue repeat-loop] to code: "goto continue_repeat"
compile [continue %var, go to next %var, on to the next %var] to code: ".."
    |goto continue_\(nomsu "var_to_lua_identifier" [%var]);

# While loops
compile [repeat while %condition %body] to code: ".."
    |do;
    |    while \(%condition as lua) do;
    |        \(%body as lua statements)
    |        ::continue_repeat::;
    |    end;
    |    ::break_repeat::;
    |end;
parse [repeat %body] as: repeat while (true) %body
parse [repeat until %condition %body] as: repeat while (not %condition) %body

# Numeric range for loops
compile [..]
    for %var from %start to %stop by %step %body
    for %var from %start to %stop via %step %body
..to code: ".."
    |do;
    |    for i=\(%start as lua),\(%stop as lua),\(%step as lua) do;
    # This trashes the loop variables, just like in Python.
    |        \(%var as lua) = i;
    |        \(%body as lua statements)
    |        ::continue_for::;
    |        ::continue_\(nomsu "var_to_lua_identifier" [%var])::;
    |    end;
    |    ::break_for::;
    |    ::break_\(nomsu "var_to_lua_identifier" [%var])::;
    |end;
parse [for %var from %start to %stop %body] as: for %var from %start to %stop via 1 %body
parse [..]
    for all %start to %stop by %step %body
    for all %start to %stop via %step %body
..as: for % from %start to %stop via %step %body
parse [for all %start to %stop %body] as: for all %start to %stop via 1 %body

compile [for %var in %iterable %body] to code:
    ".."
        |do;
        |    for i,value in ipairs(\(%iterable as lua)) do;
        # This trashes the loop variables, just like in Python.
        |        \(%var as lua) = value;
        |        \(%body as lua statements)
        |        ::continue_for::;
        |        ::continue_\(nomsu "var_to_lua_identifier" [%var])::;
        |    end;
        |    ::break_for::;
        |    ::break_\(nomsu "var_to_lua_identifier" [%var])::;
        |end;
parse [for all %iterable %body] as: for % in %iterable %body


# Switch statement/multi-branch if
compile [when %body] to code:
    %result = "do;\n"
    %fallthroughs = []
    for %func-call in (%body's "value"):
        assert ((%func-call's "type") == "FunctionCall") ".."
            |Invalid format for 'when' statement. Only '*' blocks are allowed.
        %tokens = (%func-call's "value")
        %star = (%tokens -> 1)
        assert (lua expr "vars.star and vars.star.type == 'Word' and vars.star.value == '*'") ".."
            |Invalid format for 'when' statement. Lines must begin with '*'

        %condition = (%tokens -> 2)
        assert %condition ".."
            |Invalid format for 'when' statement. Lines must begin with '*' and have a condition or the word "else"

        %action = (%tokens -> 3)
        if (%action == (nil)):
            lua block "table.insert(vars.fallthroughs, vars.condition)"
            go to next %func-call

        if (lua expr "vars.condition.type == 'Word' and vars.condition.value == 'else'"):
            %result join= ".."
                |
                |do;
        ..else:
            %condition = (%condition as lua)
            for all %fallthroughs:
                %condition join= " or \(% as lua)"
            %result join= ".."
                |
                |if \(%condition) then;
        %result join= ".."
            |
            |    \(%action as lua statements)
            |    goto finished_when;
            |end;

        %fallthroughs = []

    %result join= "\n::finished_when::;\nend;"
    %result

# Switch statement
compile [when %branch-value == ? %body] to code:
    %result = "do;\nlocal branch_value = \(%branch-value as lua)"
    %fallthroughs = []
    for %func-call in (%body's "value"):
        assert ((%func-call's "type") == "FunctionCall") ".."
            |Invalid format for 'when' statement. Only '*' blocks are allowed.
        %tokens = (%func-call's "value")
        %star = (%tokens -> 1)
        assert (lua expr "vars.star and vars.star.type == 'Word' and vars.star.value == '*'") ".."
            |Invalid format for 'when' statement. Lines must begin with '*'

        %condition = (%tokens -> 2)
        assert %condition ".."
            |Invalid format for 'when' statement. Lines must begin with '*' and have a condition or the word "else"

        %action = (%tokens -> 3)
        if (%action == (nil)):
            lua block "table.insert(vars.fallthroughs, vars.condition)"
            go to next %func-call

        if (lua expr "vars.condition.type == 'Word' and vars.condition.value == 'else'"):
            %result join= ".."
                |
                |do;
        ..else:
            %condition = "branch_value == (\(%condition as lua))"
            for all %fallthroughs:
                %condition join= " or (branch_value == \(% as lua))"
            %result join= ".."
                |
                |if \(%condition) then;
        %result join= ".."
            |
            |    \(%action as lua statements)
            |    goto finished_when;
            |end;

        %fallthroughs = []

    %result join= "\n::finished_when::;\nend;"
    %result