mal/ps/step4_if_fn_do.ps

(types.ps) run
(reader.ps) run

% read
/READ {
    /str exch def
    str read_str
} def


% eval
/eval_ast { 2 dict begin
    /env exch def
    /ast exch def
    %(eval_ast: ) print ast ==
    /nametype ast type eq { %if symbol
        env ast env_get
    }{ /arraytype ast type eq { %elseif list
        [
            ast {
                env EVAL
            } forall
        ]
    }{ % else
        ast
    } ifelse } ifelse
end } def

/EVAL { 9 dict begin
    /env exch def
    /ast exch def
    %(EVAL: ) print ast ==
    /arraytype ast type ne { %if not a list
        ast env eval_ast
    }{ %else apply the list
        /a0 ast 0 get def
        /def! a0 eq { %if def!
            /a1 ast 1 get def
            /a2 ast 2 get def
            env a1  a2 env EVAL  env_set
        }{ /let* a0 eq { %if let*
            /a1 ast 1 get def
            /a2 ast 2 get def
            /let_env env [ ] [ ] env_new def
            0 2 a1 length 1 sub { %for each pair
                /idx exch def
                let_env
                    a1 idx get
                    a1 idx 1 add get let_env EVAL
                    env_set
            } for
            a2 let_env EVAL
        }{ /do a0 eq { %if do
            /el ast _rest env eval_ast def
            el el length 1 sub get % return last value
        }{ /if a0 eq { %if if
            /a1 ast 1 get def
            /cond a1 env EVAL def
            cond null eq cond false eq or { % if cond is nil or false
                ast length 3 gt { %if false branch (a3) provided
                    ast 3 get env EVAL % EVAL false branch (a3)
                }{
                    null
                } ifelse
            }{
                ast 2 get env EVAL % EVAL true branch (a2)
            } ifelse
        }{ /fn* a0 eq { %if fn*
            /a1 ast 1 get def
            /a2 ast 2 get def
            {   /user_defined  % mark this as user defined
                __PARAMS__ __AST__ __ENV__ % closed over variables
                4 dict begin
                /ENV    exch def % closed over above, pos 3
                /AST    exch def % closed over above, pos 2
                /PARAMS exch def % closed over above, pos 1
                /args   exch def
                %(inside fn*:\n) print
                %(  A1: ) print A1 ==
                %(  A2: ) print A2 ==
                %(  ENV: ) print ENV ==
                %(  args: ) print args ==
                AST   ENV PARAMS args env_new   EVAL
            end }
            dup length array copy cvx % make an actual copy/new instance
            dup 1 a1 put  % insert closed over a1 into position 1
            dup 2 a2 put  % insert closed over a2 into position 2
            dup 3 env put % insert closed over env into position 3
        }{
            /el ast env eval_ast def
            el _rest % args array
            el _first cvx % function
            %(vvv\n) print pstack (^^^\n) print
            exec % apply function to args
        } ifelse } ifelse } ifelse } ifelse } ifelse
    } ifelse
end } def


% print
/PRINT {
    true _pr_str
} def


% repl
/repl_env null [ ] [ ] env_new def

/RE { READ repl_env EVAL } def
/REP { READ repl_env EVAL PRINT } def
/_ref { repl_env 3 1 roll env_set pop } def

types_ns { _ref } forall

(\(def! not \(fn* \(a\) \(if a false true\)\)\)) RE pop

/stdin (%stdin) (r) file def 

{ % loop
    (user> ) print flush

    stdin 99 string readline

    not { exit } if  % exit if EOF

    %(\ngot line: ) print dup print (\n) print flush

    { %try
        REP print (\n) print
    } stopped {
        (Error: ) print
        get_error_data false _pr_str print (\n) print
        clear
    } if
} bind loop

(\n) print  % final newline before exit for cleanliness
quit