Tips and Traps for DrScheme

This page is a collections of (hopefully) helpful tips and traps when running DrScheme. If you have anything you'd like to add to or modify on this page, please send an e-mail!

Common errors

• Too many parantheses - Since an open paranthesis, "(", indicates the beginning of a function, too many paranthesis will cause DrScheme to try to evaluate the result of the inner paranthesis as if it were a function, causing the error message: "illegal application: first term in application must be a function name".
  
  
• Too few paranthesis - Such as leaving off the correct number of paranthesis at the end of your function definition. The paranthesis-matching capabilities of DrScheme are designed to minimize this error, so pay attention to the highlighting that takes place as you type in paranthesis. The error message generated is "syntax error: missing close paren" or "syntax error: too many close parens".
  
  
• Misspellings - Typographical errors will give a reference to undefined identifier: [xxxx] error.
  
  
• Improper define syntax - An incorrect syntax in a define statement may lead to a define: malformed definition error.

Error Message Interpretations

• illegal application: first term in application must be a function name - The first argument after the paranthesis must be a function. This error is generated by ((+ 3 4)).
  
  
• syntax error: missing close paren - The closing paranthesis is missing. The mis-matched opening paranthesis is highlighted by DrScheme. This error is generated by (+ 5 (* 3 4) .
  
  
• syntax error: too many close parens - The opening paranthesis is missing. The mis-matched closing paranthesis is highlighted by DrScheme. This error is generated by + 5 (* 3 4)) .
  
  
• illegal application: first term in application is a function-bound identifier - This error occurs in the "Beginning Student" level because function input parameters that are functions is not allowed. For example, it is generated by (define (fn x y) (x y)) because x needs to be a function.
  
  
• reference to undefined identifier: [xxxx] - This means that xxxx was misspelled. The misspelled word is highlighted by DrScheme. Note that this may mean that there is a space missing betwen two words. For example, the error is generated by (*4 5) where "*4" misspelled due to a missing space.
  
  
• define: malformed definition - Incorrect syntax used in a define statement. For instance, (define fn(x) (* x 5)) will generate the error. It should be, (define (fn x) (* x 5)).

What does it mean when DrScheme says...?

• #i[number] - the number is an inexact value. That is, math errors may result from it because an approximation to the correct value has been used. For example pi prints out as #i3.141592653589793.

Written by Stephen Wong
Last updated: August 27, 2001