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examples: vfmt calculator.v
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Charadon
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@ -1,134 +1,135 @@
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// Q: What's this?
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// A: This is a mini "home-made" calculator. You may also regard it as a very elementary version of "interpreter".
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import os
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const (
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numeric_char = [`0`,`1`,`2`,`3`,`4`,`5`,`6`,`7`,`8`,`9`,`.`,`e`,`E`]
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)
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// Convert expression to Reverse Polish Notation.
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fn expr_to_rev_pol(expr string) ?[]string {
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if expr == '' {
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return error('err: empty expression')
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}
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mut stack := []string{}
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mut rev_pol := []string{}
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mut pos := 0
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for pos<expr.len {
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mut end_pos := pos
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for end_pos<expr.len && expr[end_pos] in numeric_char {
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end_pos++
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}
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if end_pos>pos {
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stack << expr[pos..end_pos]
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pos = end_pos
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}
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else if end_pos==pos {
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op := expr[pos].str()
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match op {
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'(' {
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stack << op
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}
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'*', '/' {
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for stack.len>0 && stack.last() !in ['(', '+', '-'] {
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rev_pol << stack.last()
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stack.delete(stack.len-1)
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}
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stack << op
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}
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'+', '-' {
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for stack.len>0 && stack.last() != '(' {
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rev_pol << stack.last()
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stack.delete(stack.len-1)
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}
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stack << op
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}
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')' {
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for stack.len>0 && stack.last() != '(' {
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rev_pol << stack.last()
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stack.delete(stack.len-1)
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}
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stack.delete(stack.len-1)
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}
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else {
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return error('err: invalid character `${op}`')
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}
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}
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pos++
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}
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}
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for stack.len>0 {
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top := stack.last()
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rev_pol << top
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stack.delete(stack.len-1)
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}
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return rev_pol
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}
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// Evaluate the result of Reverse Polish Notation.
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fn eval_rev_pol(rev_pol []string) ?f64 {
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mut stack := []f64{}
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for item in rev_pol {
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if is_num_string(item) {
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stack << item.f64()
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}
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else {
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if stack.len>=2 {
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oprand_r := stack.last()
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stack.delete(stack.len-1)
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oprand_l := stack.last()
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stack.delete(stack.len-1)
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match item {
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'+' { stack << oprand_l+oprand_r }
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'-' { stack << oprand_l-oprand_r }
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'*' { stack << oprand_l*oprand_r }
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'/' {
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if oprand_r == 0 {
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return error('err: divide by zero')
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}
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stack << oprand_l/oprand_r
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}
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else {}
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}
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}
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else {
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return error('err: invalid expression')
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}
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}
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}
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return stack[0]
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}
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fn is_num_string(str string) bool {
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for c in str {
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if c !in numeric_char {
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return false
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}
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}
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return true
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}
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fn main() {
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println('Please enter the expression you want to calculate, e.g. 1e2+(3-2.5)*6/1.5 .')
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println('Enter \'exit\' or \'EXIT\' to quit.')
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mut expr_count := 0
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for {
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expr_count++
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print('[$expr_count] ')
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expr := os.get_line().trim_space()
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if expr in ['exit', 'EXIT'] {
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break
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}
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rev_pol := expr_to_rev_pol(expr) or {
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eprintln(err)
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continue
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}
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res := eval_rev_pol(rev_pol) or {
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eprintln(err)
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continue
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}
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println(res)
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}
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}
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// Q: What's this?
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// A: This is a mini "home-made" calculator. You may also regard it as a very elementary version of "interpreter".
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import os
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const (
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numeric_char = [`0`, `1`, `2`, `3`, `4`, `5`, `6`, `7`, `8`, `9`, `.`, `e`, `E`]
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)
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// Convert expression to Reverse Polish Notation.
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fn expr_to_rev_pol(expr string) ?[]string {
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if expr == '' {
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return error('err: empty expression')
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}
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mut stack := []string{}
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mut rev_pol := []string{}
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mut pos := 0
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for pos < expr.len {
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mut end_pos := pos
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for end_pos < expr.len && expr[end_pos] in numeric_char {
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end_pos++
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}
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if end_pos > pos {
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stack << expr[pos..end_pos]
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pos = end_pos
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} else if end_pos == pos {
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op := expr[pos].str()
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match op {
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'(' {
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stack << op
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}
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'*', '/' {
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for stack.len > 0 && stack.last() !in ['(', '+', '-'] {
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rev_pol << stack.last()
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stack.delete(stack.len - 1)
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}
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stack << op
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}
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'+', '-' {
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for stack.len > 0 && stack.last() != '(' {
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rev_pol << stack.last()
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stack.delete(stack.len - 1)
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}
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stack << op
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}
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')' {
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for stack.len > 0 && stack.last() != '(' {
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rev_pol << stack.last()
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stack.delete(stack.len - 1)
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}
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stack.delete(stack.len - 1)
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}
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else {
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return error('err: invalid character `$op`')
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}
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}
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pos++
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}
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}
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for stack.len > 0 {
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top := stack.last()
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rev_pol << top
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stack.delete(stack.len - 1)
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}
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return rev_pol
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}
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// Evaluate the result of Reverse Polish Notation.
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fn eval_rev_pol(rev_pol []string) ?f64 {
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mut stack := []f64{}
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for item in rev_pol {
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if is_num_string(item) {
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stack << item.f64()
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} else {
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if stack.len >= 2 {
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oprand_r := stack.last()
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stack.delete(stack.len - 1)
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oprand_l := stack.last()
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stack.delete(stack.len - 1)
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match item {
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'+' {
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stack << oprand_l + oprand_r
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}
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'-' {
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stack << oprand_l - oprand_r
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}
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'*' {
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stack << oprand_l * oprand_r
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}
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'/' {
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if oprand_r == 0 {
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return error('err: divide by zero')
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}
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stack << oprand_l / oprand_r
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}
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else {}
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}
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} else {
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return error('err: invalid expression')
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}
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}
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}
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return stack[0]
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}
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fn is_num_string(str string) bool {
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for c in str {
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if c !in numeric_char {
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return false
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}
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}
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return true
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}
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fn main() {
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println('Please enter the expression you want to calculate, e.g. 1e2+(3-2.5)*6/1.5 .')
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println("Enter \'exit\' or \'EXIT\' to quit.")
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mut expr_count := 0
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for {
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expr_count++
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print('[$expr_count] ')
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expr := os.get_line().trim_space()
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if expr in ['exit', 'EXIT'] {
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break
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}
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rev_pol := expr_to_rev_pol(expr) or {
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eprintln(err)
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continue
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}
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res := eval_rev_pol(rev_pol) or {
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eprintln(err)
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continue
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}
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println(res)
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}
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}
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