examples: fix brainvuck.v (handle [ and ] properly); allow both brainvuck.v wasm_codegen/bf_compiler.v to work with .b files too

examples/brainvuck.v

@@ -1,66 +1,159 @@
 import os
+import term
 
-fn main() {
-	if os.args.len < 2 {
-		eprintln('you need to supply a brainfuck program as a string argument')
-		exit(1) // exit with non-zero exit code if there is no program to run
-	}
-	program := os.args[1] // our program is fed in as a string
+// For a more detailed description of the brainfuck language, see:
+// https://en.wikipedia.org/wiki/Brainfuck
+// http://brainfuck.org/brainfuck.html ,
+// http://brainfuck.org/epistle.html ,
+// http://www.hevanet.com/cristofd/brainfuck/ .
 
-	mut memory := []u8{len: 256} // we have 256 bytes of memory
-	mut address := u8(0) // as well as an 8-bit address register
+const show_state = os.getenv('VERBOSE') != ''
 
-	mut stack := []int{} // our stack does not need a maximum length
+struct BFState {
+mut:
+	pc      u16         // program counter (PC) register
+	address u16         // a 16-bit address register, serving as an index to the memory below
+	program string      // the BF program
+	memory  []u8 = []u8{len: 65536} // we have 2^16 bytes of memory
+	targets map[int]int // a mapping for the program address of a `[` to its corresponding `]`, and from a `]` to its corresponding opening `[`.
+}
 
-	mut program_counter := 0 // program counter
+fn BFState.new(program string) &BFState {
+	mut state := &BFState{
+		program: program
+	}
+	state.find_matching_pairs()
+	return state
+}
 
-	// interpreter starts here
-	for program_counter < program.len {
-		// we look at what the current character our program counter is seeing
-		match program[program_counter] {
-			`>` {
-				address++ // increment the address
+// show the current state of an BF interpreter. Useful for debugging.
+fn (state &BFState) show() {
+	println('PC: ${state.pc}')
+	println('Address: ${state.address}')
+	mut max_non_zero_address := -1
+	for i := state.memory.len - 1; i >= 0; i-- {
+		if state.memory[i] != 0 {
+			max_non_zero_address = i
+			break
 		}
-			`<` {
-				address-- // decrement the address
 	}
-			`+` {
-				memory[address]++ // increment the value at the address
-			}
-			`-` {
-				memory[address]-- // decrement the value at the address
-			}
-			`.` {
-				print(memory[address].ascii_str()) // print the value at the address
-			}
-			`,` {
-				input := os.input_opt('') or { '' } // read value and account for errors
-				memory[address] = input[0] // this is so we can ignore newlines
-				// because strings are 0-terminated, it also gives us a default value for free!
+	println('Memory: ${state.memory#[0..max_non_zero_address + 1]}')
+	println('Memory[Address]: ${state.memory#[state.address..state.address + 1]}')
 }
+
+// find_matching_pairs fills in the `targets` mapping for all pairs of `[` and `]`,
+// so that when interpreting, we would not have to search for them anymore.
+fn (mut state BFState) find_matching_pairs() {
+	mut stack := []int{}
+	for i in 0 .. state.program.len {
+		pi := state.program[i]
+		match pi {
 			`[` {
-				stack << program_counter // add loop start address to the call stack
+				stack << i
 			}
 			`]` {
-				if memory[address] != 0 {
-					// set the program counter to the last loop start
-					// so it jumps back and loops again
-					program_counter = stack[stack.len - 1]
-				} else {
-					// otherwise remove the address from the stack and continue
-					stack.pop()
+				if stack.len == 0 {
+					eprintln('> unmatched `]` found in the program, at position: ${i}')
+					eprintln('program so far:')
+					eprintln(state.program#[0..i + 1])
+					exit(1)
 				}
+				pc := stack.pop()
+				state.targets[pc] = i + 1
+				state.targets[i] = pc + 1
+				// eprintln('>>> found `[` at i $i; pc: $pc')
+			}
+			else {}
+		}
+	}
+	if stack.len > 0 {
+		eprintln('> found ${stack.len} unmatched `[`:')
+		for i in stack {
+			eprintln('  `[` at position: ${i}, program so far: `${state.program#[0..i + 1]}`')
+		}
+		exit(1)
+	}
+}
+
+[noreturn]
+fn (state &BFState) panic_for_bracket(b1 rune, b2 rune) {
+	panic('unbalanced `${b1}` found, its target `${b2}` is not known; address: ${state.address}, pc: ${state.pc}')
+}
+
+fn (mut state BFState) run() ? {
+	// the BF interpreter starts here:
+	for state.pc < state.program.len {
+		// get the current program character (corresponding to our program counter), and interpret it according to BF's rules:
+		match state.program[state.pc] {
+			`>` {
+				state.address++ // increment the address
+			}
+			`<` {
+				state.address-- // decrement the address
+			}
+			`+` {
+				state.memory[state.address]++ // increment the value at the address
+			}
+			`-` {
+				state.memory[state.address]-- // decrement the value at the address
+			}
+			`.` {
+				print(rune(state.memory[state.address])) // print the value at the address
+				flush_stdout() // ensure that even single characters are printed immediately, and not buffered
+			}
+			`,` {
+				inp := u8(term.utf8_getchar() or { 0 }) // read a character value from the standard input/terminal
+				state.memory[state.address] = inp
+			}
+			`[` {
+				if state.memory[state.address] == 0 {
+					state.pc = u16(state.targets[state.pc])
+					continue
+				}
+			}
+			`]` {
+				if state.memory[state.address] != 0 {
+					state.pc = u16(state.targets[state.pc])
+					continue
+				}
+			}
+			`#` {
+				state.show()
 			}
 			else {
-				// the interpreter should ignore characters that are not part of the language
+				// The interpreter should ignore characters that are not part of the language.
+				// I.e. they are treated like programmer comments.
 			}
 		}
 		// increment the program counter to go to the next instruction
-		program_counter++
-		// back to line 20!
+		state.pc++
+		// go back to the line `for state.pc < state.program.len {`
+	}
 }
 
-	// print the state of the interpreter at the end
-	println('Address: ${address}')
-	println('Memory: ${memory}')
+[noreturn]
+fn show_usage() {
+	eprintln('you need to supply a brainfuck program/expression as a string argument,')
+	eprintln('or filename.b, if it is located in a file (note the `.b` extension).')
+	exit(1) // exit with non-zero exit code if there is no program to run
+}
+
+fn main() {
+	if os.args.len < 2 {
+		show_usage()
+	}
+	mut program := os.args[1] // our program is fed in as a string
+	if program.ends_with('.b') {
+		program = os.read_file(program) or {
+			eprintln('error reading file ${program}: ${err}')
+			show_usage()
+		}
+	}
+
+	mut state := BFState.new(program)
+	state.run()
+
+	if show_state {
+		state.show()
+	}
 }

examples/wasm_codegen/bf_compiler.v

@@ -104,13 +104,19 @@ fn generate_code(mut start wasm.Function, bf_expr string) {
 
 @[noreturn]
 fn usage() {
-	eprintln('Usage: bf <expr> <outfile>')
+	eprintln('Usage: bf <expr> <outfile.wasm>')
+	eprintln('   or: bf <path/input.b> <outfile.wasm> (note the `.b` extension)')
 	exit(1)
 }
 
 fn main() {
-	bf_expr := os.args[1] or { usage() }
-
+	mut bf_expr := os.args[1] or { usage() }
+	if bf_expr.ends_with('.b') {
+		bf_expr = os.read_file(bf_expr) or {
+			eprintln('file ${bf_expr} could not be read, error: ${err}')
+			usage()
+		}
+	}
 	outfile := os.args[2] or { usage() }
 
 	mut m := wasm.Module{}