nimforum mirror - mathexpr, a math expression evaluator library in Nim

Tiberium (orginal) [2017-09-24T17:50:17+02:00] view original

https://github.com/Yardanico/nim-mathexpr

This is a mathematic expression evaluator library in pure Nim (with no third-party dependencies).

Basically it is a recursive descent evaluator.

It supports many mathematical functions, also you can provide variables and add custom functions.

Also it doesn't have strict rules on arguments, so all of these are valid:

sqrt(max(1, 2))
sqrt(max(1 2))
sqrt max(1, 2)
sqrt max(1 2)

# You can even do something like this!
sqrt fac log2 10

Example REPL:

## An example REPL for Mathexpr:
import strutils, rdstdin, tables, mathexpr

# Our variables (they will be available in the REPL)
var ourVars = {"x": 5.0, "y": 6.0, "z": 75.0}.newTable()

# Procedure should have this type:
# proc(args: seq[float]): float
proc mySum(args: seq[float]): float =
  for arg in args: result += arg

# Add our custom `sum` function
mathexpr.functions["sum"] = mySum

while true:
  var expr: string
  try:
    expr = readLineFromStdin("> ")
  except IOError:
    echo "Goodbye!"
    quit()
  
  if expr in ["exit", "quit", "quit()", "exit()"]:
    quit(0)
  try:
    let result = eval(expr, ourVars)
    echo "$1 = $2" % [expr, $result]
  except:
    echo getCurrentExceptionMsg()
    continue

By the way, implementation is less than 200 lines and it works in JS backend :)

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