DrRacket Tips and Traps
Common errors
- Too many paranthesesparentheses - Since an open paranthesis, "(", indicates the beginning of a function, too many paranthesis will cause DrScheme DrRacket 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
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- parenthesis - Such as leaving off the correct number of
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- parenthesis at the end of your function definition. The
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- parenthesis-matching capabilities of
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- DrRacket are designed to minimize this error, so pay attention to the highlighting that takes place as you type in
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- parenthesis. The error message generated is
syntax error: missing close parenorsyntax error: too many close parens
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- Misspellings
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- -
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- Typographical
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- errors
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- will
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- give
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- a
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reference
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to
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undefined
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identifier:
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[xxxx
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]
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- error.
- Improper define syntax - An incorrect syntax in a define statement may lead to a
define: malformed definitionerror.
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)), where there is an extra set of parentheses.syntax error: missing close paren- The closing paranthesis is missing. The mis-matched opening paranthesis is highlighted by DrSchemeDrRacket. 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 DrSchemeDrRacket. 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))becausexneeds becausexneeds to be a function.reference to undefined identifier:[xxxx]- This means thatxxxxwas misspelled. The misspelled word is highlighted by DrSchemeDrRacket. Note that this may mean that there is a space missing betwen two words. For example, the error is generated by(*4 5)where*4is "misspelled" due to a missing space.define: malformed definition- Incorrect syntax used in adefinestatement. For instance,(define fn
(x) (* x 5))will generate the error. It should be ,(define (fn x) (* x 5)).
What does it mean when
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DrRacket 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 examplepiprints out as#i3.141592653589793.