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 block: ".."
    |while \(%condition as lua) do
    |    \(%body as lua statements)
    |    ::continue_repeat::
    |end
    |::break_repeat::
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 block: ".."
    |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])::
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 block:
    ".."
        |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])::
parse (for all %iterable %body) as: for % in %iterable %body


# Switch statement/multi-branch if
compile (when %body) to block:
    %result =: ""
    %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::"
    %result

# Switch statement
compile (when %branch-value == ? %body) to block:
    %result =: "local 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::"
    %result