opr 0, a : execute operation a (13 operations: RETURN, 5 math functions, and 7 comparison functions) lod l, a : load variable l,a sto l, a : store variable l,a cal l, a : call procedure a at level l int 0, a : increment t-register by a jmp 0, a : jump to a jpc 0, a : jump conditional to a This is the code for the machine, written in Pascal: const amax=2047; {maximum address} levmax=3; {maximum depth of block nesting} cxmax=200; {size of code array} type fct=(lit,opr,lod,sto,cal,int,jmp,jpc); instruction=packed record f:fct; l:0..levmax; a:0..amax; end; var code: array [0..cxmax] of instruction; procedure interpret; const stacksize = 500; var p, b, t: integer; {program-, base-, topstack-registers} i: instruction; {instruction register} s: array [1..stacksize] of integer; {datastore} function base(l: integer): integer; var b1: integer; begin b1 := b; {find base l levels down} while l > 0 do begin b1 := s[b1]; l := l - 1 end; base := b1 end {base}; begin writeln(' start pl/0'); t := 0; b := 1; p := 0; s[1] := 0; s[2] := 0; s[3] := 0; repeat i := code[p]; p := p + 1; with i do case f of lit: begin t := t + 1; s[t] := a end; opr: case a of {operator} 0: begin {return} t := b - 1; p := s[t + 3]; b := s[t + 2]; end; 1: s[t] := -s[t]; 2: begin t := t - 1; s[t] := s[t] + s[t + 1] end; 3: begin t := t - 1; s[t] := s[t] - s[t + 1] end; 4: begin t := t - 1; s[t] := s[t] * s[t + 1] end; 5: begin t := t - 1; s[t] := s[t] div s[t + 1] end; 6: s[t] := ord(odd(s[t])); 8: begin t := t - 1; s[t] := ord(s[t] = s[t + 1]) end; 9: begin t := t - 1; s[t] := ord(s[t] <> s[t + 1]) end; 10: begin t := t - 1; s[t] := ord(s[t] < s[t + 1]) end; 11: begin t := t - 1; s[t] := ord(s[t] >= s[t + 1]) end; 12: begin t := t - 1; s[t] := ord(s[t] > s[t + 1]) end; 13: begin t := t - 1; s[t] := ord(s[t] <= s[t + 1]) end; end; lod: begin t := t +