nomsu/lib/control_flow.nom

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

# Conditionals
parse (if %condition %if_body) as lua code ".."
    |if \(%condition) then
    |    \(lua expr "vars.if_body.value")
    |end

parse (if %condition %if_body else %else_body) as lua code ".."
    |if \(%condition) then
    |    \(lua expr "vars.if_body.value")
    |else
    |    \(lua expr "vars.else_body.value")
    |end

# Return
parse (return) as lua code "do return end"
parse (return %return-value) as lua code "do return \(%return-value)"
parse (do %action) as lua expr ".."
    |(\(%action))(nomsu, setmetatable({}, {__index=vars}))


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

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

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

# While loops
parse (repeat %body) as lua block ".."
    |while true do
    |    \(lua expr "vars.body.value")
    |    ::continue_repeat::
    |end
    |::break_repeat::
parse (repeat while %condition %body) as lua block ".."
    |while \(%condition) do
    |    \(lua expr "vars.body.value")
    |    ::continue_repeat::
    |end
    |::break_repeat::
parse (repeat until %condition %body) as lua block ".."
    |while not (\(%condition)) do
    |    \(lua expr "vars.body.value")
    |    ::continue_repeat::
    |end
    |::break_repeat::

# Numeric range for loops
parse:
    for %var from %start to %stop by %step %body
    for %var from %start to %stop via %step %body
..as lua block ".."
    |for i=\(%start),\(%stop),\(%step) do
    # This trashes the loop variables, just like in Python.
    |    \(%var) = i
    |    \(lua expr "vars.body.value")
    |    ::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

parse (for %var in %iterable %body) as lua block ".."
    |for i,value in ipairs(\(%iterable)) do
    # This trashes the loop variables, just like in Python.
    |    \(%var) = value
    |    \(lua expr "vars.body.value")
    |    ::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
parse (when %body) as lua block:
    %result =: ""
    %fallthroughs =: []
    for %statement in (lua expr "vars.body.value.value"):
        %func-call =: lua expr "vars.statement.value"
        assert ((lua expr "vars['func-call'].type") == "FunctionCall") ".."
            |Invalid format for 'when' statement. Only '*' blocks are allowed.
        %tokens =: lua expr "vars['func-call'].value"

        %star =: lua expr "vars.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 =: lua expr "vars.tokens[2]"
        assert %condition ".."
            |Invalid format for 'when' statement. Lines must begin with '*' and have a condition or the word "else"

        %thunk =: lua expr "vars.tokens[3]"
        if (%thunk == (nil)):
            lua block "table.insert(vars.fallthroughs, vars.condition)"
            go to next %statement

        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 \(%)"
            %result join=: ".."
                |
                |if \(%condition) then
        %result join=: ".."
            |
            |    \(lua expr "vars.thunk.value")
            |    goto finished_when
            |end

        %fallthroughs =: []

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

# Switch statement
parse (when %branch-value == ? %body) as lua block:
    %result =: "local branch_value = \(%branch-value)"
    %fallthroughs =: []
    for %statement in (lua expr "vars.body.value.value"):
        %func-call =: lua expr "vars.statement.value"
        assert ((lua expr "vars['func-call'].type") == "FunctionCall") ".."
            |Invalid format for 'when' statement. Only '*' blocks are allowed.
        %tokens =: lua expr "vars['func-call'].value"

        %star =: lua expr "vars.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 =: lua expr "vars.tokens[2]"
        assert %condition ".."
            |Invalid format for 'when' statement. Lines must begin with '*' and have a condition or the word "else"

        %thunk =: lua expr "vars.tokens[3]"
        if (%thunk == (nil)):
            lua block "table.insert(vars.fallthroughs, vars.condition)"
            go to next %statement

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

        %fallthroughs =: []

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